Subject: Re: [PATCH 6/8] KVM: PPC: Add support for multiple-TCE hcalls

From: Alexey Kardashevskiy <[email-masked]>
Date: Thu, 11 Jul 2013 20:54:33 +1000

On 07/11/2013 08:11 PM, Alexander Graf wrote:
> 
> On 11.07.2013, at 07:12, Alexey Kardashevskiy wrote:
> 
>> On 07/10/2013 08:05 PM, Alexander Graf wrote:
>>>
>>> On 10.07.2013, at 07:00, Alexey Kardashevskiy wrote:
>>>
>>>> On 07/10/2013 03:02 AM, Alexander Graf wrote:
>>>>> On 07/06/2013 05:07 PM, Alexey Kardashevskiy wrote:
>>>>>> This adds real mode handlers for the H_PUT_TCE_INDIRECT and
>>>>>> H_STUFF_TCE hypercalls for QEMU emulated devices such as IBMVIO
>>>>>> devices or emulated PCI.  These calls allow adding multiple entries
>>>>>> (up to 512) into the TCE table in one call which saves time on
>>>>>> transition to/from real mode.
>>>>>
>>>>> We don't mention QEMU explicitly in KVM code usually.
>>>>>
>>>>>> This adds a tce_tmp cache to kvm_vcpu_arch to save valid TCEs
>>>>>> (copied from user and verified) before writing the whole list into
>>>>>> the TCE table. This cache will be utilized more in the upcoming
>>>>>> VFIO/IOMMU support to continue TCE list processing in the virtual
>>>>>> mode in the case if the real mode handler failed for some reason.
>>>>>>
>>>>>> This adds a guest physical to host real address converter
>>>>>> and calls the existing H_PUT_TCE handler. The converting function
>>>>>> is going to be fully utilized by upcoming VFIO supporting patches.
>>>>>>
>>>>>> This also implements the KVM_CAP_PPC_MULTITCE capability,
>>>>>> so in order to support the functionality of this patch, QEMU
>>>>>> needs to query for this capability and set the "hcall-multi-tce"
>>>>>> hypertas property only if the capability is present, otherwise
>>>>>> there will be serious performance degradation.
>>>>>
>>>>> Same as above. But really you're only giving recommendations here. What's
>>>>> the point? Please describe what the benefit of this patch is, not what some
>>>>> other random subsystem might do with the benefits it brings.
>>>>>
>>>>>>
>>>>>> Signed-off-by: Paul Mackerras<[email-masked]>
>>>>>> Signed-off-by: Alexey Kardashevskiy<[email-masked]>
>>>>>>
>>>>>> ---
>>>>>> Changelog:
>>>>>> 2013/07/06:
>>>>>> * fixed number of wrong get_page()/put_page() calls
>>>>>>
>>>>>> 2013/06/27:
>>>>>> * fixed clear of BUSY bit in kvmppc_lookup_pte()
>>>>>> * H_PUT_TCE_INDIRECT does realmode_get_page() now
>>>>>> * KVM_CAP_SPAPR_MULTITCE now depends on CONFIG_PPC_BOOK3S_64
>>>>>> * updated doc
>>>>>>
>>>>>> 2013/06/05:
>>>>>> * fixed mistype about IBMVIO in the commit message
>>>>>> * updated doc and moved it to another section
>>>>>> * changed capability number
>>>>>>
>>>>>> 2013/05/21:
>>>>>> * added kvm_vcpu_arch::tce_tmp
>>>>>> * removed cleanup if put_indirect failed, instead we do not even start
>>>>>> writing to TCE table if we cannot get TCEs from the user and they are
>>>>>> invalid
>>>>>> * kvmppc_emulated_h_put_tce is split to kvmppc_emulated_put_tce
>>>>>> and kvmppc_emulated_validate_tce (for the previous item)
>>>>>> * fixed bug with failthrough for H_IPI
>>>>>> * removed all get_user() from real mode handlers
>>>>>> * kvmppc_lookup_pte() added (instead of making lookup_linux_pte public)
>>>>>>
>>>>>> Signed-off-by: Alexey Kardashevskiy<[email-masked]>
>>>>>> ---
>>>>>> Documentation/virtual/kvm/api.txt       |  25 +++
>>>>>> arch/powerpc/include/asm/kvm_host.h     |   9 ++
>>>>>> arch/powerpc/include/asm/kvm_ppc.h      |  16 +-
>>>>>> arch/powerpc/kvm/book3s_64_vio.c        | 154 ++++++++++++++++++-
>>>>>> arch/powerpc/kvm/book3s_64_vio_hv.c     | 260
>>>>>> ++++++++++++++++++++++++++++----
>>>>>> arch/powerpc/kvm/book3s_hv.c            |  41 ++++-
>>>>>> arch/powerpc/kvm/book3s_hv_rmhandlers.S |   6 +
>>>>>> arch/powerpc/kvm/book3s_pr_papr.c       |  37 ++++-
>>>>>> arch/powerpc/kvm/powerpc.c              |   3 +
>>>>>> 9 files changed, 517 insertions(+), 34 deletions(-)
>>>>>>
>>>>>> diff --git a/Documentation/virtual/kvm/api.txt
>>>>>> b/Documentation/virtual/kvm/api.txt
>>>>>> index 6365fef..762c703 100644
>>>>>> --- a/Documentation/virtual/kvm/api.txt
>>>>>> +++ b/Documentation/virtual/kvm/api.txt
>>>>>> @@ -2362,6 +2362,31 @@ calls by the guest for that service will be passed
>>>>>> to userspace to be
>>>>>> handled.
>>>>>>
>>>>>>
>>>>>> +4.86 KVM_CAP_PPC_MULTITCE
>>>>>> +
>>>>>> +Capability: KVM_CAP_PPC_MULTITCE
>>>>>> +Architectures: ppc
>>>>>> +Type: vm
>>>>>> +
>>>>>> +This capability means the kernel is capable of handling hypercalls
>>>>>> +H_PUT_TCE_INDIRECT and H_STUFF_TCE without passing those into the user
>>>>>> +space. This significanly accelerates DMA operations for PPC KVM guests.
>>>>>
>>>>> significanly? Please run this through a spell checker.
>>>>>
>>>>>> +The user space should expect that its handlers for these hypercalls
>>>>>
>>>>> s/The//
>>>>>
>>>>>> +are not going to be called.
>>>>>
>>>>> Is user space guaranteed they will not be called? Or can it still happen?
>>>>
>>>> ... if user space previously registered LIOBN in KVM (via
>>>> KVM_CREATE_SPAPR_TCE or similar calls).
>>>>
>>>> ok?
>>>
>>> How about this?
>>>
>>> The hypercalls mentioned above may or may not be processed successfully in the kernel based fast path. If they can not be handled by the kernel, they will get passed on to user space. So user space still has to have an implementation for these despite the in kernel acceleration.
>>>
>>> ---
>>>
>>> The target audience for this documentation is user space KVM API users. Someone developing kvm tool for example. They want to know implications specific CAPs have.
>>>
>>>>
>>>> There is also KVM_CREATE_SPAPR_TCE_IOMMU but it is not in the kernel yet
>>>> and may never get there.
>>>>
>>>>
>>>>>> +In order to enable H_PUT_TCE_INDIRECT and H_STUFF_TCE use in the guest,
>>>>>> +the user space might have to advertise it for the guest. For example,
>>>>>> +IBM pSeries guest starts using them if "hcall-multi-tce" is present in
>>>>>> +the "ibm,hypertas-functions" device-tree property.
>>>>>
>>>>> This paragraph describes sPAPR. That's fine, but please document it as
>>>>> such. Also please check your grammar.
>>>>
>>>>>> +
>>>>>> +Without this capability, only H_PUT_TCE is handled by the kernel and
>>>>>> +therefore the use of H_PUT_TCE_INDIRECT and H_STUFF_TCE is not recommended
>>>>>> +unless the capability is present as passing hypercalls to the userspace
>>>>>> +slows operations a lot.
>>>>>> +
>>>>>> +Unlike other capabilities of this section, this one is always enabled.
>>>>>
>>>>> Why? Wouldn't that confuse older user space?
>>>>
>>>>
>>>> How? Old user space won't check for this capability and won't tell the
>>>> guest to use it (via "hcall-multi-tce"). Old H_PUT_TCE is still there.
>>>>
>>>> If the guest always uses H_PUT_TCE_INDIRECT/H_STUFF_TCE no matter what,
>>>> then it is its problem - it won't work now anyway as neither QEMU nor host
>>>> kernel supports these calls.
>>
>>
>>> Always assume that you are a kernel developer without knowledge
>>> of any user space code using your interfaces. So there is the theoretical
>>> possibility that there is a user space client out there that implements
>>> H_PUT_TCE_INDIRECT and advertises hcall-multi-tce to the guest. 
>>> Would that client break? If so, we should definitely have
>>> the CAP disabled by default.
>>
>>
>> No, it won't break. Why would it break? I really do not get it. This user
>> space client has to do an extra step to get this acceleration by calling
>> ioctl(KVM_CREATE_SPAPR_TCE) anyway. Previously that ioctl only had effect
>> on H_PUT_TCE, now on all three hcalls.
> 
> Hrm. It's a change of behavior, it probably wouldn't break, yes.

Aaand?

>>> But really, it's also as much about consistency as anything else.
>>> If we leave everything as is and always extend functionality
>>> by enabling new CAPs, we're pretty much guaranteed that we
>>> don't break anything by accident. It also makes debugging easier
>>> because you can for example disable this particular feature
>>> to see whether something has bad side effects.
>>
>>
>> So I must add one more ioctl to enable MULTITCE in kernel handling. Is it
>> what you are saying?
>>
>> I can see KVM_CHECK_EXTENSION but I do not see KVM_ENABLE_EXTENSION or
>> anything like that.
> 
> KVM_ENABLE_CAP. It's how we enable sPAPR capabilities too.

Yeah, Paul already explained. It is platform specific but ok.
And does not have "EXTENSION" in the name for some reason but ok too.

KVM_ENABLE_CAP is vcpu ioctl. So kvm_arch_vcpu_ioctl() enables VCPU's
capabilities while KVM_CAP_SPAPR_MULTITCE is KVM (or more precisely
SPAPR-TCE/LIOBN but I really do not want it to be that specific) capability.

Sure I can add to kvm_arch_vcpu_ioctl():

case KVM_CAP_SPAPR_MULTITCE:
        r = 0;
        vcpu->kvm->arch.spapr_multitce_enabled = cap->args[0];
        break;

But I suspect you and Ben will call it ugly. SO do I have to implement
KVM_ENABLE_CAP in kvm_arch_vm_ioctl and change the api.txt that it is not
just about vcpu ioctl anymore? Or my brand new ioctl for this?

>>>>>> +
>>>>>> +
>>>>>> 5. The kvm_run structure
>>>>>> ------------------------
>>>>>>
>>>>>> diff --git a/arch/powerpc/include/asm/kvm_host.h
>>>>>> b/arch/powerpc/include/asm/kvm_host.h
>>>>>> index af326cd..20d04bd 100644
>>>>>> --- a/arch/powerpc/include/asm/kvm_host.h
>>>>>> +++ b/arch/powerpc/include/asm/kvm_host.h
>>>>>> @@ -180,6 +180,7 @@ struct kvmppc_spapr_tce_table {
>>>>>>     struct kvm *kvm;
>>>>>>     u64 liobn;
>>>>>>     u32 window_size;
>>>>>> +    struct { struct { unsigned long put, indir, stuff; } rm, vm; } stat;
>>>>>
>>>>> You don't need this.
>>>>>
>>>>>>     struct page *pages[0];
>>>>>> };
>>>>>>
>>>>>> @@ -609,6 +610,14 @@ struct kvm_vcpu_arch {
>>>>>>     spinlock_t tbacct_lock;
>>>>>>     u64 busy_stolen;
>>>>>>     u64 busy_preempt;
>>>>>> +
>>>>>> +    unsigned long *tce_tmp_hpas;    /* TCE cache for TCE_PUT_INDIRECT
>>>>>> hcall */
>>>>>> +    enum {
>>>>>> +        TCERM_NONE,
>>>>>> +        TCERM_GETPAGE,
>>>>>> +        TCERM_PUTTCE,
>>>>>> +        TCERM_PUTLIST,
>>>>>> +    } tce_rm_fail;            /* failed stage of request processing */
>>>>>> #endif
>>>>>> };
>>>>>>
>>>>>> diff --git a/arch/powerpc/include/asm/kvm_ppc.h
>>>>>> b/arch/powerpc/include/asm/kvm_ppc.h
>>>>>> index a5287fe..fa722a0 100644
>>>>>> --- a/arch/powerpc/include/asm/kvm_ppc.h
>>>>>> +++ b/arch/powerpc/include/asm/kvm_ppc.h
>>>>>> @@ -133,8 +133,20 @@ extern int kvmppc_pseries_do_hcall(struct kvm_vcpu
>>>>>> *vcpu);
>>>>>>
>>>>>> extern long kvm_vm_ioctl_create_spapr_tce(struct kvm *kvm,
>>>>>>                 struct kvm_create_spapr_tce *args);
>>>>>> -extern long kvmppc_h_put_tce(struct kvm_vcpu *vcpu, unsigned long liobn,
>>>>>> -                 unsigned long ioba, unsigned long tce);
>>>>>> +extern struct kvmppc_spapr_tce_table *kvmppc_find_tce_table(
>>>>>> +        struct kvm_vcpu *vcpu, unsigned long liobn);
>>>>>> +extern long kvmppc_emulated_validate_tce(unsigned long tce);
>>>>>> +extern void kvmppc_emulated_put_tce(struct kvmppc_spapr_tce_table *tt,
>>>>>> +        unsigned long ioba, unsigned long tce);
>>>>>> +extern long kvmppc_vm_h_put_tce(struct kvm_vcpu *vcpu,
>>>>>> +        unsigned long liobn, unsigned long ioba,
>>>>>> +        unsigned long tce);
>>>>>> +extern long kvmppc_vm_h_put_tce_indirect(struct kvm_vcpu *vcpu,
>>>>>> +        unsigned long liobn, unsigned long ioba,
>>>>>> +        unsigned long tce_list, unsigned long npages);
>>>>>> +extern long kvmppc_vm_h_stuff_tce(struct kvm_vcpu *vcpu,
>>>>>> +        unsigned long liobn, unsigned long ioba,
>>>>>> +        unsigned long tce_value, unsigned long npages);
>>>>>> extern long kvm_vm_ioctl_allocate_rma(struct kvm *kvm,
>>>>>>                 struct kvm_allocate_rma *rma);
>>>>>> extern struct kvmppc_linear_info *kvm_alloc_rma(void);
>>>>>> diff --git a/arch/powerpc/kvm/book3s_64_vio.c
>>>>>> b/arch/powerpc/kvm/book3s_64_vio.c
>>>>>> index b2d3f3b..99bf4e5 100644
>>>>>> --- a/arch/powerpc/kvm/book3s_64_vio.c
>>>>>> +++ b/arch/powerpc/kvm/book3s_64_vio.c
>>>>>> @@ -14,6 +14,7 @@
>>>>>>  *
>>>>>>  * Copyright 2010 Paul Mackerras, IBM Corp.<[email-masked]>
>>>>>>  * Copyright 2011 David Gibson, IBM Corporation<[email-masked]>
>>>>>> + * Copyright 2013 Alexey Kardashevskiy, IBM Corporation<[email-masked]>
>>>>>>  */
>>>>>>
>>>>>> #include<linux/types.h>
>>>>>> @@ -36,8 +37,10 @@
>>>>>> #include<asm/ppc-opcode.h>
>>>>>> #include<asm/kvm_host.h>
>>>>>> #include<asm/udbg.h>
>>>>>> +#include<asm/iommu.h>
>>>>>> +#include<asm/tce.h>
>>>>>>
>>>>>> -#define TCES_PER_PAGE    (PAGE_SIZE / sizeof(u64))
>>>>>> +#define ERROR_ADDR      ((void *)~(unsigned long)0x0)
>>>>>>
>>>>>> static long kvmppc_stt_npages(unsigned long window_size)
>>>>>> {
>>>>>> @@ -50,6 +53,20 @@ static void release_spapr_tce_table(struct
>>>>>> kvmppc_spapr_tce_table *stt)
>>>>>>     struct kvm *kvm = stt->kvm;
>>>>>>     int i;
>>>>>>
>>>>>> +#define __SV(x) stt->stat.x
>>>>>> +#define __SVD(x) (__SV(rm.x)?(__SV(rm.x)-__SV(vm.x)):0)
>>>>>> +    pr_debug("%s stat for liobn=%llx\n"
>>>>>> +            "--------------- realmode ----- virtmode ---\n"
>>>>>> +            "put_tce       %10ld     %10ld\n"
>>>>>> +            "put_tce_indir %10ld     %10ld\n"
>>>>>> +            "stuff_tce     %10ld     %10ld\n",
>>>>>> +            __func__, stt->liobn,
>>>>>> +            __SVD(put), __SV(vm.put),
>>>>>> +            __SVD(indir), __SV(vm.indir),
>>>>>> +            __SVD(stuff), __SV(vm.stuff));
>>>>>> +#undef __SVD
>>>>>> +#undef __SV
>>>>>
>>>>> All of these stat points should just be trace points. You can do the
>>>>> statistic gathering from user space then.
>>>>>
>>>>>> +
>>>>>>     mutex_lock(&kvm->lock);
>>>>>>     list_del(&stt->list);
>>>>>>     for (i = 0; i<  kvmppc_stt_npages(stt->window_size); i++)
>>>>>> @@ -148,3 +165,138 @@ fail:
>>>>>>     }
>>>>>>     return ret;
>>>>>> }
>>>>>> +
>>>>>> +/* Converts guest physical address to host virtual address */
>>>>>> +static void __user *kvmppc_vm_gpa_to_hva_and_get(struct kvm_vcpu *vcpu,
>>>>>
>>>>> Please don't distinguish _vm versions. They're the normal case. _rm ones
>>>>> are the special ones.
>>>>>
>>>>>> +        unsigned long gpa, struct page **pg)
>>>>>> +{
>>>>>> +    unsigned long hva, gfn = gpa>>  PAGE_SHIFT;
>>>>>> +    struct kvm_memory_slot *memslot;
>>>>>> +
>>>>>> +    memslot = search_memslots(kvm_memslots(vcpu->kvm), gfn);
>>>>>> +    if (!memslot)
>>>>>> +        return ERROR_ADDR;
>>>>>> +
>>>>>> +    hva = __gfn_to_hva_memslot(memslot, gfn) + (gpa&  ~PAGE_MASK);
>>>>>
>>>>> s/+/|/
>>>>>
>>>>>> +
>>>>>> +    if (get_user_pages_fast(hva&  PAGE_MASK, 1, 0, pg) != 1)
>>>>>> +        return ERROR_ADDR;
>>>>>> +
>>>>>> +    return (void *) hva;
>>>>>> +}
>>>>>> +
>>>>>> +long kvmppc_vm_h_put_tce(struct kvm_vcpu *vcpu,
>>>>>> +        unsigned long liobn, unsigned long ioba,
>>>>>> +        unsigned long tce)
>>>>>> +{
>>>>>> +    long ret;
>>>>>> +    struct kvmppc_spapr_tce_table *tt;
>>>>>> +
>>>>>> +    tt = kvmppc_find_tce_table(vcpu, liobn);
>>>>>> +    /* Didn't find the liobn, put it to userspace */
>>>>>
>>>>> Unclear comment.
>>>>
>>>>
>>>> What detail is missing?
>>>
>>
>>> Grammar wise "it" in the second half of the sentence refers to liobn.
>>> So you "put" the "liobn to userspace". That sentence doesn't
>>> make any sense.
>>
>>
>> Removed it. H_TOO_HARD itself says enough already.
>>
>>
>>> What you really want to say is:
>>>
>>>  /* Couldn't find the liobn. Something went wrong. Let user space handle the hypercall. That has better ways of dealing with errors. */
>>>
>>>>
>>>>
>>>>>> +    if (!tt)
>>>>>> +        return H_TOO_HARD;
>>>>>> +
>>>>>> +    ++tt->stat.vm.put;
>>>>>> +
>>>>>> +    if (ioba>= tt->window_size)
>>>>>> +        return H_PARAMETER;
>>>>>> +
>>>>>> +    ret = kvmppc_emulated_validate_tce(tce);
>>>>>> +    if (ret)
>>>>>> +        return ret;
>>>>>> +
>>>>>> +    kvmppc_emulated_put_tce(tt, ioba, tce);
>>>>>> +
>>>>>> +    return H_SUCCESS;
>>>>>> +}
>>>>>> +
>>>>>> +long kvmppc_vm_h_put_tce_indirect(struct kvm_vcpu *vcpu,
>>>>>> +        unsigned long liobn, unsigned long ioba,
>>>>>> +        unsigned long tce_list, unsigned long npages)
>>>>>> +{
>>>>>> +    struct kvmppc_spapr_tce_table *tt;
>>>>>> +    long i, ret = H_SUCCESS;
>>>>>> +    unsigned long __user *tces;
>>>>>> +    struct page *pg = NULL;
>>>>>> +
>>>>>> +    tt = kvmppc_find_tce_table(vcpu, liobn);
>>>>>> +    /* Didn't find the liobn, put it to userspace */
>>>>>> +    if (!tt)
>>>>>> +        return H_TOO_HARD;
>>>>>> +
>>>>>> +    ++tt->stat.vm.indir;
>>>>>> +
>>>>>> +    /*
>>>>>> +     * The spec says that the maximum size of the list is 512 TCEs so
>>>>>> +     * so the whole table addressed resides in 4K page
>>>>>
>>>>> so so?
>>>>>
>>>>>> +     */
>>>>>> +    if (npages>  512)
>>>>>> +        return H_PARAMETER;
>>>>>> +
>>>>>> +    if (tce_list&  ~IOMMU_PAGE_MASK)
>>>>>> +        return H_PARAMETER;
>>>>>> +
>>>>>> +    if ((ioba + (npages<<  IOMMU_PAGE_SHIFT))>  tt->window_size)
>>>>>> +        return H_PARAMETER;
>>>>>> +
>>>>>> +    tces = kvmppc_vm_gpa_to_hva_and_get(vcpu, tce_list,&pg);
>>>>>> +    if (tces == ERROR_ADDR)
>>>>>> +        return H_TOO_HARD;
>>>>>> +
>>>>>> +    if (vcpu->arch.tce_rm_fail == TCERM_PUTLIST)
>>>>>> +        goto put_list_page_exit;
>>>>>> +
>>>>>> +    for (i = 0; i<  npages; ++i) {
>>>>>> +        if (get_user(vcpu->arch.tce_tmp_hpas[i], tces + i)) {
>>>>>> +            ret = H_PARAMETER;
>>>>>> +            goto put_list_page_exit;
>>>>>> +        }
>>>>>> +
>>>>>> +        ret = kvmppc_emulated_validate_tce(vcpu->arch.tce_tmp_hpas[i]);
>>>>>> +        if (ret)
>>>>>> +            goto put_list_page_exit;
>>>>>> +    }
>>>>>> +
>>>>>> +    for (i = 0; i<  npages; ++i)
>>>>>> +        kvmppc_emulated_put_tce(tt, ioba + (i<<  IOMMU_PAGE_SHIFT),
>>>>>> +                vcpu->arch.tce_tmp_hpas[i]);
>>>>>> +put_list_page_exit:
>>>>>> +    if (pg)
>>>>>> +        put_page(pg);
>>>>>> +
>>>>>> +    if (vcpu->arch.tce_rm_fail != TCERM_NONE) {
>>>>>> +        vcpu->arch.tce_rm_fail = TCERM_NONE;
>>>>>> +        if (pg&&  !PageCompound(pg))
>>>>>> +            put_page(pg); /* finish pending realmode_put_page() */
>>>>>> +    }
>>>>>> +
>>>>>> +    return ret;
>>>>>> +}
>>>>>> +
>>>>>> +long kvmppc_vm_h_stuff_tce(struct kvm_vcpu *vcpu,
>>>>>> +        unsigned long liobn, unsigned long ioba,
>>>>>> +        unsigned long tce_value, unsigned long npages)
>>>>>> +{
>>>>>> +    struct kvmppc_spapr_tce_table *tt;
>>>>>> +    long i, ret;
>>>>>> +
>>>>>> +    tt = kvmppc_find_tce_table(vcpu, liobn);
>>>>>> +    /* Didn't find the liobn, put it to userspace */
>>>>>> +    if (!tt)
>>>>>> +        return H_TOO_HARD;
>>>>>> +
>>>>>> +    ++tt->stat.vm.stuff;
>>>>>> +
>>>>>> +    if ((ioba + (npages<<  IOMMU_PAGE_SHIFT))>  tt->window_size)
>>>>>> +        return H_PARAMETER;
>>>>>> +
>>>>>> +    ret = kvmppc_emulated_validate_tce(tce_value);
>>>>>> +    if (ret || (tce_value&  (TCE_PCI_WRITE | TCE_PCI_READ)))
>>>>>> +        return H_PARAMETER;
>>>>>> +
>>>>>> +    for (i = 0; i<  npages; ++i, ioba += IOMMU_PAGE_SIZE)
>>>>>> +        kvmppc_emulated_put_tce(tt, ioba, tce_value);
>>>>>> +
>>>>>> +    return H_SUCCESS;
>>>>>> +}
>>>>>> diff --git a/arch/powerpc/kvm/book3s_64_vio_hv.c
>>>>>> b/arch/powerpc/kvm/book3s_64_vio_hv.c
>>>>>> index 30c2f3b..cd3e6f9 100644
>>>>>> --- a/arch/powerpc/kvm/book3s_64_vio_hv.c
>>>>>> +++ b/arch/powerpc/kvm/book3s_64_vio_hv.c
>>>>>> @@ -14,6 +14,7 @@
>>>>>>  *
>>>>>>  * Copyright 2010 Paul Mackerras, IBM Corp.<[email-masked]>
>>>>>>  * Copyright 2011 David Gibson, IBM Corporation<[email-masked]>
>>>>>> + * Copyright 2013 Alexey Kardashevskiy, IBM Corporation<[email-masked]>
>>>>>>  */
>>>>>>
>>>>>> #include<linux/types.h>
>>>>>> @@ -35,42 +36,243 @@
>>>>>> #include<asm/ppc-opcode.h>
>>>>>> #include<asm/kvm_host.h>
>>>>>> #include<asm/udbg.h>
>>>>>> +#include<asm/iommu.h>
>>>>>> +#include<asm/tce.h>
>>>>>>
>>>>>> #define TCES_PER_PAGE    (PAGE_SIZE / sizeof(u64))
>>>>>> +#define ERROR_ADDR      (~(unsigned long)0x0)
>>>>>>
>>>>>> -/* WARNING: This will be called in real-mode on HV KVM and virtual
>>>>>> - *          mode on PR KVM
>>>>>
>>>>> What's wrong with the warning?
>>>>
>>>>
>>>> It belongs to kvmppc_h_put_tce() which is not called in virtual mode anymore.
>>>
>>> I thought the comment applied to the whole file before? Hrm. Maybe I misread it then.
>>>
>>>> It is technically correct for kvmppc_find_tce_table() though. Should I put
>>>> this comment before every function which may be called from real and
>>>> virtual modes?
>>>
>>> Yes, please. Otherwise someone might stick an access to a non-linear address
>>> in there by accident.
>>>
>>>>
>>>>
>>>>
>>>>>> +/*
>>>>>> + * Finds a TCE table descriptor by LIOBN
>>>>>>  */
>>>>>> +struct kvmppc_spapr_tce_table *kvmppc_find_tce_table(struct kvm_vcpu *vcpu,
>>>>>> +        unsigned long liobn)
>>>>>> +{
>>>>>> +    struct kvmppc_spapr_tce_table *tt;
>>>>>> +
>>>>>> +    list_for_each_entry(tt,&vcpu->kvm->arch.spapr_tce_tables, list) {
>>>>>> +        if (tt->liobn == liobn)
>>>>>> +            return tt;
>>>>>> +    }
>>>>>> +
>>>>>> +    return NULL;
>>>>>> +}
>>>>>> +EXPORT_SYMBOL_GPL(kvmppc_find_tce_table);
>>>>>> +
>>>>>> +#ifdef DEBUG
>>>>>> +/*
>>>>>> + * Lets user mode disable realmode handlers by putting big number
>>>>>> + * in the bottom value of LIOBN
>>>>>
>>>>> What? Seriously? Just don't enable the CAP.
>>>>
>>>>
>>>> It is under DEBUG. It really, really helps to be able to disable real mode
>>>> handlers without reboot. Ok, no debug code, I'll remove.
>>>
>>> Debug code is good, but #ifdefs are bad. For you, an #ifdef reads like
>>> "code that doesn't do any hard when disabled". For me, #ifdefs read
>>> "code that definitely breaks because nobody turns the #define on".
>>>
>>> So please, avoid #ifdef'ed code whenever possible. Switching the CAP on and
>>> off is a much better debug approach in this case.
>>>
>>>>
>>>>
>>>>>> + */
>>>>>> +#define kvmppc_find_tce_table(a, b) \
>>>>>> +        ((((b)&0xffff)>10000)?NULL:kvmppc_find_tce_table((a), (b)))
>>>>>> +#endif
>>>>>> +
>>>>>> +/*
>>>>>> + * Validates TCE address.
>>>>>> + * At the moment only flags are validated as other checks will
>>>>>> significantly slow
>>>>>> + * down or can make it even impossible to handle TCE requests in real mode.
>>>>>
>>>>> What?
>>>>
>>>>
>>>> What is missing here (besides good english)?
>>>
>>> What badness could slip through by not validating everything?
>>
>>
>> I cannot think of any good check which could be done in real mode and not
>> be "more than 2 calls deep" (c) Ben. Check that the page is allocated at
>> all? How? Don't know.
> 

> If you say that our validation doesn't validate everything, that makes
> me really weary.

It checks that TCE does not have any bit set in bits 2..12. If they are
set, something went very wrong. Better than nothing.

> Could the guest use it to maliciously inject anything?
> Could a missing check make our code go berserk?

No. KVM does not do anything with those addresses, just puts them to the
table and lets QEMU or a guest deal with it.

> What checks exactly would you do in addition when this was virtual mode?

Check that TCE is within RAM boundaries. Or check that the page was
allocated. find_linux_pte_or_hugepte? It can fail in real mode but in
virtual mode I can call get_user_fast_page and confirm that the address is
ok. Not sure, did not think much about it. Compare page flags with TCE
flags if both or neither have "write" set, this kind of stuff.

I am not really sure we need any of those checks for emulated TCE at all.

Remove the comment then?

>>>>>> + */
>>>>>> +long kvmppc_emulated_validate_tce(unsigned long tce)
>>>>>
>>>>> I don't like the naming scheme. Please turn this around and make it
>>>>> kvmppc_tce_validate().
>>>>
>>>>
>>>> Oh. "Like"... Ok.
>>>
>>> Yes. Like.
>>>
>>>>
>>>>
>>>>>> +{
>>>>>> +    if (tce&  ~(IOMMU_PAGE_MASK | TCE_PCI_WRITE | TCE_PCI_READ))
>>>>>> +        return H_PARAMETER;
>>>>>> +
>>>>>> +    return H_SUCCESS;
>>>>>> +}
>>>>>> +EXPORT_SYMBOL_GPL(kvmppc_emulated_validate_tce);
>>>>>> +
>>>>>> +/*
>>>>>> + * Handles TCE requests for QEMU emulated devices.
>>>>>
>>>>> We still don't mention QEMU in KVM code. And does it really matter whether
>>>>> they're emulated by QEMU? Devices could also be emulated by KVM.
>>>>>
>>>>>> + * Puts guest TCE values to the table and expects QEMU to convert them
>>>>>> + * later in a QEMU device implementation.
>>>>>> + * Called in both real and virtual modes.
>>>>>> + * Cannot fail so kvmppc_emulated_validate_tce must be called before it.
>>>>>> + */
>>>>>> +void kvmppc_emulated_put_tce(struct kvmppc_spapr_tce_table *tt,
>>>>>
>>>>> kvmppc_tce_put()
>>>>>
>>>>>> +        unsigned long ioba, unsigned long tce)
>>>>>> +{
>>>>>> +    unsigned long idx = ioba>>  SPAPR_TCE_SHIFT;
>>>>>> +    struct page *page;
>>>>>> +    u64 *tbl;
>>>>>> +
>>>>>> +    /*
>>>>>> +     * Note on the use of page_address() in real mode,
>>>>>> +     *
>>>>>> +     * It is safe to use page_address() in real mode on ppc64 because
>>>>>> +     * page_address() is always defined as lowmem_page_address()
>>>>>> +     * which returns __va(PFN_PHYS(page_to_pfn(page))) which is arithmetial
>>>>>> +     * operation and does not access page struct.
>>>>>> +     *
>>>>>> +     * Theoretically page_address() could be defined different
>>>>>> +     * but either WANT_PAGE_VIRTUAL or HASHED_PAGE_VIRTUAL
>>>>>> +     * should be enabled.
>>>>>> +     * WANT_PAGE_VIRTUAL is never enabled on ppc32/ppc64,
>>>>>> +     * HASHED_PAGE_VIRTUAL could be enabled for ppc32 only and only
>>>>>> +     * if CONFIG_HIGHMEM is defined. As CONFIG_SPARSEMEM_VMEMMAP
>>>>>> +     * is not expected to be enabled on ppc32, page_address()
>>>>>> +     * is safe for ppc32 as well.
>>>>>> +     */
>>>>>> +#if defined(HASHED_PAGE_VIRTUAL) || defined(WANT_PAGE_VIRTUAL)
>>>>>> +#error TODO: fix to avoid page_address() here
>>>>>> +#endif
>>>>>
>>>>> Can you extract the text above, the check and the page_address call into a
>>>>> simple wrapper function?
>>>>
>>>>
>>>> Is this function also too big? Sorry, I do not understand the comment.
>>>
>>> All of the comment and #if here only deal with the fact that you
>>> have a real mode hack to call page_address() that happens
>>> to work under specific circumstances.
>>>
>>> There's nothing kvmppc_tce_put() specific about this.
>>> The page_address() code happens to get called here, sure.
>>> But if I read the kvmppc_tce_put() function I don't care about
>>> these details - I want to understand the code flow that ends
>>> up writing the TCE.
>>>
>>>>>> +    page = tt->pages[idx / TCES_PER_PAGE];
>>>>>> +    tbl = (u64 *)page_address(page);
>>>>>> +
>>>>>> +    /* udbg_printf("tce @ %p\n",&tbl[idx % TCES_PER_PAGE]); */
>>>>>
>>>>> This is not an RFC, is it?
>>>>
>>>>
>>>> Any debug code is prohibited? Ok, I'll remove.
>>>
>>> Debug code that requires code changes is prohibited, yes.
>>> Debug code that is runtime switchable (pr_debug, trace points, etc)
>>> are allowed.
>>
>>
>> Is there any easy way to enable just this specific udbg_printf (not all of
>> them at once)? Trace points do not work in real mode as we figured out.
> 
> You can enable pr_debug by file IIRC.

On already running kernel? :-/ Wow. How?

>>>>>> +    tbl[idx % TCES_PER_PAGE] = tce;
>>>>>> +}
>>>>>> +EXPORT_SYMBOL_GPL(kvmppc_emulated_put_tce);
>>>>>> +
>>>>>> +#ifdef CONFIG_KVM_BOOK3S_64_HV
>>>>>> +/*
>>>>>> + * Converts guest physical address to host physical address.
>>>>>> + * Tries to increase page counter via realmode_get_page() and
>>>>>> + * returns ERROR_ADDR if failed.
>>>>>> + */
>>>>>> +static unsigned long kvmppc_rm_gpa_to_hpa_and_get(struct kvm_vcpu *vcpu,
>>>>>> +        unsigned long gpa, struct page **pg)
>>>>>> +{
>>>>>> +    struct kvm_memory_slot *memslot;
>>>>>> +    pte_t *ptep, pte;
>>>>>> +    unsigned long hva, hpa = ERROR_ADDR;
>>>>>> +    unsigned long gfn = gpa>>  PAGE_SHIFT;
>>>>>> +    unsigned shift = 0;
>>>>>> +
>>>>>> +    memslot = search_memslots(kvm_memslots(vcpu->kvm), gfn);
>>>>>> +    if (!memslot)
>>>>>> +        return ERROR_ADDR;
>>>>>> +
>>>>>> +    hva = __gfn_to_hva_memslot(memslot, gfn);
>>>>>> +
>>>>>> +    ptep = find_linux_pte_or_hugepte(vcpu->arch.pgdir, hva,&shift);
>>>>>> +    if (!ptep || !pte_present(*ptep))
>>>>>> +        return ERROR_ADDR;
>>>>>> +    pte = *ptep;
>>>>>> +
>>>>>> +    if (((gpa&  TCE_PCI_WRITE) || pte_write(pte))&&  !pte_dirty(pte))
>>>>>> +        return ERROR_ADDR;
>>>>>> +
>>>>>> +    if (!pte_young(pte))
>>>>>> +        return ERROR_ADDR;
>>>>>> +
>>>>>> +    if (!shift)
>>>>>> +        shift = PAGE_SHIFT;
>>>>>> +
>>>>>> +    /* Put huge pages handling to the virtual mode */
>>>>>> +    if (shift>  PAGE_SHIFT)
>>>>>> +        return ERROR_ADDR;
>>>>>> +
>>>>>> +    *pg = realmode_pfn_to_page(pte_pfn(pte));
>>>>>> +    if (!*pg || realmode_get_page(*pg))
>>>>>> +        return ERROR_ADDR;
>>>>>> +
>>>>>> +    /* pte_pfn(pte) returns address aligned to pg_size */
>>>>>> +    hpa = (pte_pfn(pte)<<  PAGE_SHIFT) + (gpa&  ((1<<  shift) - 1));
>>>>>> +
>>>>>> +    if (unlikely(pte_val(pte) != pte_val(*ptep))) {
>>>>>> +        hpa = ERROR_ADDR;
>>>>>> +        realmode_put_page(*pg);
>>>>>> +        *pg = NULL;
>>>>>> +    }
>>>>>> +
>>>>>> +    return hpa;
>>>>>> +}
>>>>>> +
>>>>>> long kvmppc_h_put_tce(struct kvm_vcpu *vcpu, unsigned long liobn,
>>>>>>               unsigned long ioba, unsigned long tce)
>>>>>> {
>>>>>> -    struct kvm *kvm = vcpu->kvm;
>>>>>> -    struct kvmppc_spapr_tce_table *stt;
>>>>>> -
>>>>>> -    /* udbg_printf("H_PUT_TCE(): liobn=0x%lx ioba=0x%lx, tce=0x%lx\n", */
>>>>>> -    /*         liobn, ioba, tce); */
>>>>>> -
>>>>>> -    list_for_each_entry(stt,&kvm->arch.spapr_tce_tables, list) {
>>>>>> -        if (stt->liobn == liobn) {
>>>>>> -            unsigned long idx = ioba>>  SPAPR_TCE_SHIFT;
>>>>>> -            struct page *page;
>>>>>> -            u64 *tbl;
>>>>>> -
>>>>>> -            /* udbg_printf("H_PUT_TCE: liobn 0x%lx =>  stt=%p 
>>>>>> window_size=0x%x\n", */
>>>>>> -            /*         liobn, stt, stt->window_size); */
>>>>>> -            if (ioba>= stt->window_size)
>>>>>> -                return H_PARAMETER;
>>>>>> -
>>>>>> -            page = stt->pages[idx / TCES_PER_PAGE];
>>>>>> -            tbl = (u64 *)page_address(page);
>>>>>> -
>>>>>> -            /* FIXME: Need to validate the TCE itself */
>>>>>> -            /* udbg_printf("tce @ %p\n",&tbl[idx % TCES_PER_PAGE]); */
>>>>>> -            tbl[idx % TCES_PER_PAGE] = tce;
>>>>>> -            return H_SUCCESS;
>>>>>> -        }
>>>>>> +    long ret;
>>>>>> +    struct kvmppc_spapr_tce_table *tt = kvmppc_find_tce_table(vcpu, liobn);
>>>>>> +
>>>>>> +    if (!tt)
>>>>>> +        return H_TOO_HARD;
>>>>>> +
>>>>>> +    ++tt->stat.rm.put;
>>>>>> +
>>>>>> +    if (ioba>= tt->window_size)
>>>>>> +        return H_PARAMETER;
>>>>>> +
>>>>>> +    ret = kvmppc_emulated_validate_tce(tce);
>>>>>> +    if (!ret)
>>>>>> +        kvmppc_emulated_put_tce(tt, ioba, tce);
>>>>>> +
>>>>>> +    return ret;
>>>>>> +}
>>>>>> +
>>>>>> +long kvmppc_h_put_tce_indirect(struct kvm_vcpu *vcpu,
>>>>>
>>>>> So the _vm version is the normal one and this is the _rm version? If so,
>>>>> please mark it as such. Is there any way to generate both from the same
>>>>> source? The way it's now there is a lot of duplicate code.
>>>>
>>>>
>>>> I tried, looked very ugly. If you insist, I will do so.
>>>
>>
>>> If it looks ugly better don't. I just want to make sure you explored the option.
>>> But please keep the naming scheme consistent.
>>
>>
>> Removed _vm everywhere and put _rm in realmode handlers. I just was
>> confused by _vm in kvm_vm_ioctl_create_spapr_tce() at the first place.
> 
> That vm refers to the virtual machine. It's on VM scope, not VCPU scope.

I do not mind, just saying where it came from :)

-- 
Alexey