Subject: Re: [PATCH kernel v6 10/10] KVM: PPC: VFIO: Add in-kernel acceleration for VFIO

From: David Gibson <[email-masked]>
Date: Tue, 7 Mar 2017 23:08:41 +1100

On Tue, Mar 07, 2017 at 10:07:27PM +1100, Alexey Kardashevskiy wrote:
> On 06/03/17 16:04, Alexey Kardashevskiy wrote:
> > On 06/03/17 15:30, David Gibson wrote:
> >> On Fri, Mar 03, 2017 at 06:09:25PM +1100, Alexey Kardashevskiy wrote:
> >>> On 03/03/17 16:59, David Gibson wrote:
> >>>> On Thu, Mar 02, 2017 at 07:56:44PM +1100, Alexey Kardashevskiy wrote:
> >>>>> This allows the host kernel to handle H_PUT_TCE, H_PUT_TCE_INDIRECT
> >>>>> and H_STUFF_TCE requests targeted an IOMMU TCE table used for VFIO
> >>>>> without passing them to user space which saves time on switching
> >>>>> to user space and back.
> >>>>>
> >>>>> This adds H_PUT_TCE/H_PUT_TCE_INDIRECT/H_STUFF_TCE handlers to KVM.
> >>>>> KVM tries to handle a TCE request in the real mode, if failed
> >>>>> it passes the request to the virtual mode to complete the operation.
> >>>>> If it a virtual mode handler fails, the request is passed to
> >>>>> the user space; this is not expected to happen though.
> >>>>>
> >>>>> To avoid dealing with page use counters (which is tricky in real mode),
> >>>>> this only accelerates SPAPR TCE IOMMU v2 clients which are required
> >>>>> to pre-register the userspace memory. The very first TCE request will
> >>>>> be handled in the VFIO SPAPR TCE driver anyway as the userspace view
> >>>>> of the TCE table (iommu_table::it_userspace) is not allocated till
> >>>>> the very first mapping happens and we cannot call vmalloc in real mode.
> >>>>>
> >>>>> If we fail to update a hardware IOMMU table unexpected reason, we just
> >>>>> clear it and move on as there is nothing really we can do about it -
> >>>>> for example, if we hot plug a VFIO device to a guest, existing TCE tables
> >>>>> will be mirrored automatically to the hardware and there is no interface
> >>>>> to report to the guest about possible failures.
> >>>>>
> >>>>> This adds new attribute - KVM_DEV_VFIO_GROUP_SET_SPAPR_TCE - to
> >>>>> the VFIO KVM device. It takes a VFIO group fd and SPAPR TCE table fd
> >>>>> and associates a physical IOMMU table with the SPAPR TCE table (which
> >>>>> is a guest view of the hardware IOMMU table). The iommu_table object
> >>>>> is cached and referenced so we do not have to look up for it in real mode.
> >>>>>
> >>>>> This does not implement the UNSET counterpart as there is no use for it -
> >>>>> once the acceleration is enabled, the existing userspace won't
> >>>>> disable it unless a VFIO container is destroyed; this adds necessary
> >>>>> cleanup to the KVM_DEV_VFIO_GROUP_DEL handler.
> >>>>>
> >>>>> As this creates a descriptor per IOMMU table-LIOBN couple (called
> >>>>> kvmppc_spapr_tce_iommu_table), it is possible to have several
> >>>>> descriptors with the same iommu_table (hardware IOMMU table) attached
> >>>>> to the same LIOBN; we do not remove duplicates though as
> >>>>> iommu_table_ops::exchange not just update a TCE entry (which is
> >>>>> shared among IOMMU groups) but also invalidates the TCE cache
> >>>>> (one per IOMMU group).
> >>>>>
> >>>>> This advertises the new KVM_CAP_SPAPR_TCE_VFIO capability to the user
> >>>>> space.
> >>>>>
> >>>>> This finally makes use of vfio_external_user_iommu_id() which was
> >>>>> introduced quite some time ago and was considered for removal.
> >>>>>
> >>>>> Tests show that this patch increases transmission speed from 220MB/s
> >>>>> to 750..1020MB/s on 10Gb network (Chelsea CXGB3 10Gb ethernet card).
> >>>>>
> >>>>> Signed-off-by: Alexey Kardashevskiy <[email-masked]>
> >>>>> ---
> >>>>> Changes:
> >>>>> v6:
> >>>>> * changed handling of errors returned by kvmppc_(rm_)tce_iommu_(un)map()
> >>>>> * moved kvmppc_gpa_to_ua() to TCE validation
> >>>>>
> >>>>> v5:
> >>>>> * changed error codes in multiple places
> >>>>> * added bunch of WARN_ON() in places which should not really happen
> >>>>> * adde a check that an iommu table is not attached already to LIOBN
> >>>>> * dropped explicit calls to iommu_tce_clear_param_check/
> >>>>> iommu_tce_put_param_check as kvmppc_tce_validate/kvmppc_ioba_validate
> >>>>> call them anyway (since the previous patch)
> >>>>> * if we fail to update a hardware IOMMU table for unexpected reason,
> >>>>> this just clears the entry
> >>>>>
> >>>>> v4:
> >>>>> * added note to the commit log about allowing multiple updates of
> >>>>> the same IOMMU table;
> >>>>> * instead of checking for if any memory was preregistered, this
> >>>>> returns H_TOO_HARD if a specific page was not;
> >>>>> * fixed comments from v3 about error handling in many places;
> >>>>> * simplified TCE handlers and merged IOMMU parts inline - for example,
> >>>>> there used to be kvmppc_h_put_tce_iommu(), now it is merged into
> >>>>> kvmppc_h_put_tce(); this allows to check IOBA boundaries against
> >>>>> the first attached table only (makes the code simpler);
> >>>>>
> >>>>> v3:
> >>>>> * simplified not to use VFIO group notifiers
> >>>>> * reworked cleanup, should be cleaner/simpler now
> >>>>>
> >>>>> v2:
> >>>>> * reworked to use new VFIO notifiers
> >>>>> * now same iommu_table may appear in the list several times, to be fixed later
> >>>>> ---
> >>>>>  Documentation/virtual/kvm/devices/vfio.txt |  22 +-
> >>>>>  arch/powerpc/include/asm/kvm_host.h        |   8 +
> >>>>>  arch/powerpc/include/asm/kvm_ppc.h         |   4 +
> >>>>>  include/uapi/linux/kvm.h                   |   8 +
> >>>>>  arch/powerpc/kvm/book3s_64_vio.c           | 321 ++++++++++++++++++++++++++++-
> >>>>>  arch/powerpc/kvm/book3s_64_vio_hv.c        | 165 ++++++++++++++-
> >>>>>  arch/powerpc/kvm/powerpc.c                 |   2 +
> >>>>>  virt/kvm/vfio.c                            |  60 ++++++
> >>>>>  8 files changed, 585 insertions(+), 5 deletions(-)
> >>>>>
> >>>>> diff --git a/Documentation/virtual/kvm/devices/vfio.txt b/Documentation/virtual/kvm/devices/vfio.txt
> >>>>> index ef51740c67ca..f95d867168ea 100644
> >>>>> --- a/Documentation/virtual/kvm/devices/vfio.txt
> >>>>> +++ b/Documentation/virtual/kvm/devices/vfio.txt
> >>>>> @@ -16,7 +16,25 @@ Groups:
> >>>>>  
> >>>>>  KVM_DEV_VFIO_GROUP attributes:
> >>>>>    KVM_DEV_VFIO_GROUP_ADD: Add a VFIO group to VFIO-KVM device tracking
> >>>>> +	kvm_device_attr.addr points to an int32_t file descriptor
> >>>>> +	for the VFIO group.
> >>>>>    KVM_DEV_VFIO_GROUP_DEL: Remove a VFIO group from VFIO-KVM device tracking
> >>>>> +	kvm_device_attr.addr points to an int32_t file descriptor
> >>>>> +	for the VFIO group.
> >>>>> +  KVM_DEV_VFIO_GROUP_SET_SPAPR_TCE: attaches a guest visible TCE table
> >>>>> +	allocated by sPAPR KVM.
> >>>>> +	kvm_device_attr.addr points to a struct:
> >>>>>  
> >>>>> -For each, kvm_device_attr.addr points to an int32_t file descriptor
> >>>>> -for the VFIO group.
> >>>>> +	struct kvm_vfio_spapr_tce {
> >>>>> +		__u32	argsz;
> >>>>> +		__u32	flags;
> >>>>> +		__s32	groupfd;
> >>>>> +		__s32	tablefd;
> >>>>> +	};
> >>>>> +
> >>>>> +	where
> >>>>> +	@argsz is the size of kvm_vfio_spapr_tce_liobn;
> >>>>> +	@flags are not supported now, must be zero;
> >>>>> +	@groupfd is a file descriptor for a VFIO group;
> >>>>> +	@tablefd is a file descriptor for a TCE table allocated via
> >>>>> +		KVM_CREATE_SPAPR_TCE.
> >>>>> diff --git a/arch/powerpc/include/asm/kvm_host.h b/arch/powerpc/include/asm/kvm_host.h
> >>>>> index 7bba8f415627..857ae2c6aa39 100644
> >>>>> --- a/arch/powerpc/include/asm/kvm_host.h
> >>>>> +++ b/arch/powerpc/include/asm/kvm_host.h
> >>>>> @@ -191,6 +191,13 @@ struct kvmppc_pginfo {
> >>>>>  	atomic_t refcnt;
> >>>>>  };
> >>>>>  
> >>>>> +struct kvmppc_spapr_tce_iommu_table {
> >>>>> +	struct rcu_head rcu;
> >>>>> +	struct list_head next;
> >>>>> +	struct vfio_group *group;
> >>>>> +	struct iommu_table *tbl;
> >>>>> +};
> >>>>> +
> >>>>>  struct kvmppc_spapr_tce_table {
> >>>>>  	struct list_head list;
> >>>>>  	struct kvm *kvm;
> >>>>> @@ -199,6 +206,7 @@ struct kvmppc_spapr_tce_table {
> >>>>>  	u32 page_shift;
> >>>>>  	u64 offset;		/* in pages */
> >>>>>  	u64 size;		/* window size in pages */
> >>>>> +	struct list_head iommu_tables;
> >>>>>  	struct page *pages[0];
> >>>>>  };
> >>>>>  
> >>>>> diff --git a/arch/powerpc/include/asm/kvm_ppc.h b/arch/powerpc/include/asm/kvm_ppc.h
> >>>>> index 72c2a155641f..66de7e73b3d3 100644
> >>>>> --- a/arch/powerpc/include/asm/kvm_ppc.h
> >>>>> +++ b/arch/powerpc/include/asm/kvm_ppc.h
> >>>>> @@ -164,6 +164,10 @@ extern long kvmppc_prepare_vrma(struct kvm *kvm,
> >>>>>  extern void kvmppc_map_vrma(struct kvm_vcpu *vcpu,
> >>>>>  			struct kvm_memory_slot *memslot, unsigned long porder);
> >>>>>  extern int kvmppc_pseries_do_hcall(struct kvm_vcpu *vcpu);
> >>>>> +extern long kvm_spapr_tce_attach_iommu_group(struct kvm *kvm, int tablefd,
> >>>>> +		struct vfio_group *group);
> >>>>> +extern void kvm_spapr_tce_release_iommu_group(struct kvm *kvm,
> >>>>> +		struct vfio_group *group);
> >>>>>  
> >>>>>  extern long kvm_vm_ioctl_create_spapr_tce(struct kvm *kvm,
> >>>>>  				struct kvm_create_spapr_tce_64 *args);
> >>>>> diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
> >>>>> index f5a52ffb6b58..e743cb0d176e 100644
> >>>>> --- a/include/uapi/linux/kvm.h
> >>>>> +++ b/include/uapi/linux/kvm.h
> >>>>> @@ -1088,6 +1088,7 @@ struct kvm_device_attr {
> >>>>>  #define  KVM_DEV_VFIO_GROUP			1
> >>>>>  #define   KVM_DEV_VFIO_GROUP_ADD			1
> >>>>>  #define   KVM_DEV_VFIO_GROUP_DEL			2
> >>>>> +#define   KVM_DEV_VFIO_GROUP_SET_SPAPR_TCE		3
> >>>>>  
> >>>>>  enum kvm_device_type {
> >>>>>  	KVM_DEV_TYPE_FSL_MPIC_20	= 1,
> >>>>> @@ -1109,6 +1110,13 @@ enum kvm_device_type {
> >>>>>  	KVM_DEV_TYPE_MAX,
> >>>>>  };
> >>>>>  
> >>>>> +struct kvm_vfio_spapr_tce {
> >>>>> +	__u32	argsz;
> >>>>> +	__u32	flags;
> >>>>> +	__s32	groupfd;
> >>>>> +	__s32	tablefd;
> >>>>> +};
> >>>>> +
> >>>>>  /*
> >>>>>   * ioctls for VM fds
> >>>>>   */
> >>>>> diff --git a/arch/powerpc/kvm/book3s_64_vio.c b/arch/powerpc/kvm/book3s_64_vio.c
> >>>>> index 57dd036bd998..85927f467811 100644
> >>>>> --- a/arch/powerpc/kvm/book3s_64_vio.c
> >>>>> +++ b/arch/powerpc/kvm/book3s_64_vio.c
> >>>>> @@ -27,6 +27,10 @@
> >>>>>  #include <linux/hugetlb.h>
> >>>>>  #include <linux/list.h>
> >>>>>  #include <linux/anon_inodes.h>
> >>>>> +#include <linux/iommu.h>
> >>>>> +#include <linux/file.h>
> >>>>> +#include <linux/vfio.h>
> >>>>> +#include <linux/module.h>
> >>>>>  
> >>>>>  #include <asm/tlbflush.h>
> >>>>>  #include <asm/kvm_ppc.h>
> >>>>> @@ -39,6 +43,36 @@
> >>>>>  #include <asm/udbg.h>
> >>>>>  #include <asm/iommu.h>
> >>>>>  #include <asm/tce.h>
> >>>>> +#include <asm/mmu_context.h>
> >>>>> +
> >>>>> +static void kvm_vfio_group_put_external_user(struct vfio_group *vfio_group)
> >>>>> +{
> >>>>> +	void (*fn)(struct vfio_group *);
> >>>>> +
> >>>>> +	fn = symbol_get(vfio_group_put_external_user);
> >>>>> +	if (WARN_ON(!fn))
> >>>>> +		return;
> >>>>> +
> >>>>> +	fn(vfio_group);
> >>>>> +
> >>>>> +	symbol_put(vfio_group_put_external_user);
> >>>>> +}
> >>>>> +
> >>>>> +static int kvm_vfio_external_user_iommu_id(struct vfio_group *vfio_group)
> >>>>> +{
> >>>>> +	int (*fn)(struct vfio_group *);
> >>>>> +	int ret = -1;
> >>>>> +
> >>>>> +	fn = symbol_get(vfio_external_user_iommu_id);
> >>>>> +	if (!fn)
> >>>>> +		return ret;
> >>>>> +
> >>>>> +	ret = fn(vfio_group);
> >>>>> +
> >>>>> +	symbol_put(vfio_external_user_iommu_id);
> >>>>> +
> >>>>> +	return ret;
> >>>>> +}
> >>>>>  
> >>>>>  static unsigned long kvmppc_tce_pages(unsigned long iommu_pages)
> >>>>>  {
> >>>>> @@ -90,6 +124,130 @@ static long kvmppc_account_memlimit(unsigned long stt_pages, bool inc)
> >>>>>  	return ret;
> >>>>>  }
> >>>>>  
> >>>>> +static void kvm_spapr_tce_iommu_table_free(struct rcu_head *head)
> >>>>> +{
> >>>>> +	struct kvmppc_spapr_tce_iommu_table *stit = container_of(head,
> >>>>> +			struct kvmppc_spapr_tce_iommu_table, rcu);
> >>>>> +
> >>>>> +	iommu_table_put(stit->tbl);
> >>>>> +	kvm_vfio_group_put_external_user(stit->group);
> >>>>> +
> >>>>> +	kfree(stit);
> >>>>> +}
> >>>>> +
> >>>>> +static void kvm_spapr_tce_liobn_release_iommu_group(
> >>>>> +		struct kvmppc_spapr_tce_table *stt,
> >>>>> +		struct vfio_group *group)
> >>>>> +{
> >>>>> +	struct kvmppc_spapr_tce_iommu_table *stit, *tmp;
> >>>>> +
> >>>>> +	list_for_each_entry_safe(stit, tmp, &stt->iommu_tables, next) {
> >>>>> +		if (group && (stit->group != group))
> >>>>> +			continue;
> >>>>> +
> >>>>> +		list_del_rcu(&stit->next);
> >>>>> +
> >>>>> +		call_rcu(&stit->rcu, kvm_spapr_tce_iommu_table_free);
> >>>>> +	}
> >>>>> +}
> >>>>> +
> >>>>> +extern void kvm_spapr_tce_release_iommu_group(struct kvm *kvm,
> >>>>> +		struct vfio_group *group)
> >>>>> +{
> >>>>> +	struct kvmppc_spapr_tce_table *stt;
> >>>>> +
> >>>>> +	list_for_each_entry_rcu(stt, &kvm->arch.spapr_tce_tables, list)
> >>>>> +		kvm_spapr_tce_liobn_release_iommu_group(stt, group);
> >>>>> +}
> >>>>> +
> >>>>> +extern long kvm_spapr_tce_attach_iommu_group(struct kvm *kvm, int tablefd,
> >>>>> +		struct vfio_group *group)
> >>>>> +{
> >>>>> +	struct kvmppc_spapr_tce_table *stt = NULL;
> >>>>> +	bool found = false;
> >>>>> +	struct iommu_table *tbl = NULL;
> >>>>> +	struct iommu_table_group *table_group;
> >>>>> +	long i, ret = 0;
> >>>>> +	struct kvmppc_spapr_tce_iommu_table *stit;
> >>>>> +	struct fd f;
> >>>>> +	int group_id;
> >>>>> +	struct iommu_group *grp;
> >>>>> +
> >>>>> +	group_id = kvm_vfio_external_user_iommu_id(group);
> >>>>> +	grp = iommu_group_get_by_id(group_id);
> >>>>> +	if (WARN_ON(!grp))
> >>>>> +		return -EIO;
> >>>>> +
> >>>>> +	f = fdget(tablefd);
> >>>>> +	if (!f.file) {
> >>>>> +		ret = -EBADF;
> >>>>> +		goto put_exit;
> >>>>> +	}
> >>>>> +
> >>>>> +	list_for_each_entry_rcu(stt, &kvm->arch.spapr_tce_tables, list) {
> >>>>> +		if (stt == f.file->private_data) {
> >>>>> +			found = true;
> >>>>> +			break;
> >>>>> +		}
> >>>>> +	}
> >>>>> +
> >>>>> +	fdput(f);
> >>>>> +
> >>>>> +	if (!found) {
> >>>>> +		ret = -EINVAL;
> >>>>> +		goto put_exit;
> >>>>> +	}
> >>>>> +
> >>>>> +	table_group = iommu_group_get_iommudata(grp);
> >>>>> +	if (WARN_ON(!table_group)) {
> >>>>> +		ret = -EFAULT;
> >>>>> +		goto put_exit;
> >>>>> +	}
> >>>>> +
> >>>>> +	for (i = 0; i < IOMMU_TABLE_GROUP_MAX_TABLES; ++i) {
> >>>>> +		struct iommu_table *tbltmp = table_group->tables[i];
> >>>>> +
> >>>>> +		if (!tbltmp)
> >>>>> +			continue;
> >>>>> +
> >>>>> +		/*
> >>>>> +		 * Make sure hardware table parameters are exactly the same;
> >>>>> +		 * this is used in the TCE handlers where boundary checks
> >>>>> +		 * use only the first attached table.
> >>>>> +		 */
> >>>>> +		if ((tbltmp->it_page_shift == stt->page_shift) &&
> >>>>> +				(tbltmp->it_offset == stt->offset) &&
> >>>>> +				(tbltmp->it_size == stt->size)) {
> >>>>> +			tbl = tbltmp;
> >>>>> +			break;
> >>>>> +		}
> >>>>> +	}
> >>>>> +	if (!tbl) {
> >>>>> +		ret = -EINVAL;
> >>>>> +		goto put_exit;
> >>>>> +	}
> >>>>> +
> >>>>> +	list_for_each_entry_rcu(stit, &stt->iommu_tables, next) {
> >>>>> +		if ((stit->tbl == tbl) && (stit->group == group)) {
> >>>>> +			ret = -EBUSY;
> >>>>> +			goto put_exit;
> >>>>> +		}
> >>>>> +	}
> >>>>> +
> >>>>> +	iommu_table_get(tbl);
> >>>>> +
> >>>>> +	stit = kzalloc(sizeof(*stit), GFP_KERNEL);
> >>>>> +	stit->tbl = tbl;
> >>>>> +	stit->group = group;
> >>>>> +
> >>>>> +	list_add_rcu(&stit->next, &stt->iommu_tables);
> >>>>> +
> >>>>> +put_exit:
> >>>>> +	iommu_group_put(grp);
> >>>>> +
> >>>>> +	return ret;
> >>>>> +}
> >>>>> +
> >>>>>  static void release_spapr_tce_table(struct rcu_head *head)
> >>>>>  {
> >>>>>  	struct kvmppc_spapr_tce_table *stt = container_of(head,
> >>>>> @@ -132,6 +290,8 @@ static int kvm_spapr_tce_release(struct inode *inode, struct file *filp)
> >>>>>  
> >>>>>  	list_del_rcu(&stt->list);
> >>>>>  
> >>>>> +	kvm_spapr_tce_liobn_release_iommu_group(stt, NULL /* release all */);
> >>>>> +
> >>>>>  	kvm_put_kvm(stt->kvm);
> >>>>>  
> >>>>>  	kvmppc_account_memlimit(
> >>>>> @@ -182,6 +342,7 @@ long kvm_vm_ioctl_create_spapr_tce(struct kvm *kvm,
> >>>>>  	stt->offset = args->offset;
> >>>>>  	stt->size = size;
> >>>>>  	stt->kvm = kvm;
> >>>>> +	INIT_LIST_HEAD_RCU(&stt->iommu_tables);
> >>>>>  
> >>>>>  	for (i = 0; i < npages; i++) {
> >>>>>  		stt->pages[i] = alloc_page(GFP_KERNEL | __GFP_ZERO);
> >>>>> @@ -210,11 +371,99 @@ long kvm_vm_ioctl_create_spapr_tce(struct kvm *kvm,
> >>>>>  	return ret;
> >>>>>  }
> >>>>>  
> >>>>> +static void kvmppc_clear_tce(struct iommu_table *tbl, unsigned long entry)
> >>>>> +{
> >>>>> +	unsigned long hpa = 0;
> >>>>> +	enum dma_data_direction dir = DMA_NONE;
> >>>>> +
> >>>>> +	iommu_tce_xchg(tbl, entry, &hpa, &dir);
> >>>>> +}
> >>>>> +
> >>>>> +static long kvmppc_tce_iommu_mapped_dec(struct kvm *kvm,
> >>>>> +		struct iommu_table *tbl, unsigned long entry)
> >>>>> +{
> >>>>> +	struct mm_iommu_table_group_mem_t *mem = NULL;
> >>>>> +	const unsigned long pgsize = 1ULL << tbl->it_page_shift;
> >>>>> +	unsigned long *pua = IOMMU_TABLE_USERSPACE_ENTRY(tbl, entry);
> >>>>> +
> >>>>> +	if (WARN_ON_ONCE(!pua))
> >>>>> +		return H_HARDWARE;
> >>>>> +
> >>>>> +	mem = mm_iommu_lookup(kvm->mm, *pua, pgsize);
> >>>>> +	if (!mem)
> >>>>> +		return H_TOO_HARD;
> >>>>> +
> >>>>> +	mm_iommu_mapped_dec(mem);
> >>>>> +
> >>>>> +	*pua = 0;
> >>>>> +
> >>>>> +	return H_SUCCESS;
> >>>>> +}
> >>>>> +
> >>>>> +static long kvmppc_tce_iommu_unmap(struct kvm *kvm,
> >>>>> +		struct iommu_table *tbl, unsigned long entry)
> >>>>> +{
> >>>>> +	enum dma_data_direction dir = DMA_NONE;
> >>>>> +	unsigned long hpa = 0;
> >>>>> +	long ret;
> >>>>> +
> >>>>> +	if (iommu_tce_xchg(tbl, entry, &hpa, &dir))
> >>>>> +		return H_HARDWARE;
> >>>>> +
> >>>>> +	if (dir == DMA_NONE)
> >>>>> +		return H_SUCCESS;
> >>>>> +
> >>>>> +	ret = kvmppc_tce_iommu_mapped_dec(kvm, tbl, entry);
> >>>>> +	if (ret != H_SUCCESS)
> >>>>> +		iommu_tce_xchg(tbl, entry, &hpa, &dir);
> >>>>> +
> >>>>> +	return ret;
> >>>>> +}
> >>>>> +
> >>>>> +long kvmppc_tce_iommu_map(struct kvm *kvm, struct iommu_table *tbl,
> >>>>> +		unsigned long entry, unsigned long ua,
> >>>>> +		enum dma_data_direction dir)
> >>>>> +{
> >>>>> +	long ret;
> >>>>> +	unsigned long hpa, *pua = IOMMU_TABLE_USERSPACE_ENTRY(tbl, entry);
> >>>>> +	struct mm_iommu_table_group_mem_t *mem;
> >>>>> +
> >>>>> +	if (!pua)
> >>>>> +		/* it_userspace allocation might be delayed */
> >>>>> +		return H_TOO_HARD;
> >>>>> +
> >>>>> +	mem = mm_iommu_lookup(kvm->mm, ua, 1ULL << tbl->it_page_shift);
> >>>>> +	if (!mem)
> >>>>> +		return H_TOO_HARD;
> >>>>
> >>>> IIUC this is the virtual mode path, not the real mode patch.  Under
> >>>> what circumstances could qemu succeed that KVM virtual mode couldn't,
> >>>> for either of the above failures?
> >>>
> >>> The (!pua) failure is handled in tce_iommu_build_v2() from
> >>> drivers/vfio/vfio_iommu_spapr_tce.c as:
> >>>
> >>>
> >>> if (!tbl->it_userspace) {
> >>>        ret = tce_iommu_userspace_view_alloc(tbl, container->mm);
> >>>        if (ret)
> >>>               return ret;
> >>> }
> >>
> >> Ah.. which is called from the ioctl() path but not the KVM hcall path,
> >> ok, I get it.
> >>
> >>> The (!mem) can succeed if the container is in VFIO_SPAPR_TCE_IOMMU mode
> >>> (not VFIO_SPAPR_TCE_v2_IOMMU). Remember that the userspace can call
> >>> ioctl(vfio_kvm_device, KVM_DEV_VFIO_GROUP_SET_SPAPR_TCE) without having
> >>> memory preregistered so tables will appear in the
> >>> kvmppc_spapr_tce_iommu_table list in KVM.
> >>
> >> Ok.  So in short, the userspace->ioctl() path will handle both v1 and
> >> v2 versions of the IOMMU interface, whereas the in-kernel
> >> implementation (both real and virtual) will only handle v2.  Is that
> >> right?
> > 
> > 
> > Correct. I used to have an explicit check for any memory preregistered, now
> > it is as bit less obvious but still the case.
> > 
> > 
> > 
> > 
> >>
> >>>>> +
> >>>>> +	if (WARN_ON_ONCE(mm_iommu_ua_to_hpa(mem, ua, &hpa)))
> >>>>> +		return H_HARDWARE;
> >>>>> +
> >>>>> +	if (mm_iommu_mapped_inc(mem))
> >>>>> +		return H_CLOSED;
> >>>>> +
> >>>>> +	ret = iommu_tce_xchg(tbl, entry, &hpa, &dir);
> >>>>> +	if (ret) {
> >>>>
> >>>> It thought the xchg could basically never fail, so this should be
> >>>> another WARN_ON().
> >>>
> >>>
> >>> Correct.
> >>>
> >>>
> >>>>> +		mm_iommu_mapped_dec(mem);
> >>>>> +		return H_TOO_HARD;
> >>>>> +	}
> >>>>> +
> >>>>> +	if (dir != DMA_NONE)
> >>>>> +		kvmppc_tce_iommu_mapped_dec(kvm, tbl, entry);
> >>>>> +
> >>>>> +	*pua = ua;
> >>>>> +
> >>>>> +	return 0;
> >>>>> +}
> >>>>> +
> >>>>>  long kvmppc_h_put_tce(struct kvm_vcpu *vcpu, unsigned long liobn,
> >>>>>  		      unsigned long ioba, unsigned long tce)
> >>>>>  {
> >>>>>  	struct kvmppc_spapr_tce_table *stt;
> >>>>> -	long ret;
> >>>>> +	long ret, idx;
> >>>>> +	struct kvmppc_spapr_tce_iommu_table *stit;
> >>>>> +	unsigned long entry, ua = 0;
> >>>>> +	enum dma_data_direction dir;
> >>>>>  
> >>>>>  	/* udbg_printf("H_PUT_TCE(): liobn=0x%lx ioba=0x%lx, tce=0x%lx\n", */
> >>>>>  	/* 	    liobn, ioba, tce); */
> >>>>> @@ -231,7 +480,35 @@ long kvmppc_h_put_tce(struct kvm_vcpu *vcpu, unsigned long liobn,
> >>>>>  	if (ret != H_SUCCESS)
> >>>>>  		return ret;
> >>>>>  
> >>>>> -	kvmppc_tce_put(stt, ioba >> stt->page_shift, tce);
> >>>>> +	dir = iommu_tce_direction(tce);
> >>>>> +	if ((dir != DMA_NONE) && kvmppc_gpa_to_ua(vcpu->kvm,
> >>>>> +			tce & ~(TCE_PCI_READ | TCE_PCI_WRITE), &ua, NULL))
> >>>>> +		return H_PARAMETER;
> >>>>> +
> >>>>> +	entry = ioba >> stt->page_shift;
> >>>>> +
> >>>>> +	list_for_each_entry_lockless(stit, &stt->iommu_tables, next) {
> >>>>> +		if (dir == DMA_NONE) {
> >>>>> +			ret = kvmppc_tce_iommu_unmap(vcpu->kvm,
> >>>>> +					stit->tbl, entry);
> >>>>> +		} else {
> >>>>> +			idx = srcu_read_lock(&vcpu->kvm->srcu);
> >>>>> +			ret = kvmppc_tce_iommu_map(vcpu->kvm, stit->tbl,
> >>>>> +					entry, ua, dir);
> >>>>> +			srcu_read_unlock(&vcpu->kvm->srcu, idx);
> >>>>> +		}
> >>>>> +
> >>>>> +		if (ret == H_SUCCESS)
> >>>>> +			continue;
> >>>>> +
> >>>>> +		if (ret == H_TOO_HARD)
> >>>>> +			return ret;
> >>>>> +
> >>>>> +		WARN_ON_ONCE(1);
> >>>>> +		kvmppc_clear_tce(stit->tbl, entry);
> >>>>> +	}
> >>>>> +
> >>>>> +	kvmppc_tce_put(stt, entry, tce);
> >>>>>  
> >>>>>  	return H_SUCCESS;
> >>>>>  }
> >>>>> @@ -246,6 +523,7 @@ long kvmppc_h_put_tce_indirect(struct kvm_vcpu *vcpu,
> >>>>>  	unsigned long entry, ua = 0;
> >>>>>  	u64 __user *tces;
> >>>>>  	u64 tce;
> >>>>> +	struct kvmppc_spapr_tce_iommu_table *stit;
> >>>>>  
> >>>>>  	stt = kvmppc_find_table(vcpu->kvm, liobn);
> >>>>>  	if (!stt)
> >>>>> @@ -284,6 +562,26 @@ long kvmppc_h_put_tce_indirect(struct kvm_vcpu *vcpu,
> >>>>>  		if (ret != H_SUCCESS)
> >>>>>  			goto unlock_exit;
> >>>>>  
> >>>>> +		if (kvmppc_gpa_to_ua(vcpu->kvm,
> >>>>> +				tce & ~(TCE_PCI_READ | TCE_PCI_WRITE),
> >>>>> +				&ua, NULL))
> >>>>> +			return H_PARAMETER;
> >>>>> +
> >>>>> +		list_for_each_entry_lockless(stit, &stt->iommu_tables, next) {
> >>>>> +			ret = kvmppc_tce_iommu_map(vcpu->kvm,
> >>>>> +					stit->tbl, entry + i, ua,
> >>>>> +					iommu_tce_direction(tce));
> >>>>> +
> >>>>> +			if (ret == H_SUCCESS)
> >>>>> +				continue;
> >>>>> +
> >>>>> +			if (ret == H_TOO_HARD)
> >>>>> +				goto unlock_exit;
> >>>>> +
> >>>>> +			WARN_ON_ONCE(1);
> >>>>> +			kvmppc_clear_tce(stit->tbl, entry);
> >>>>> +		}
> >>>>> +
> >>>>>  		kvmppc_tce_put(stt, entry + i, tce);
> >>>>>  	}
> >>>>>  
> >>>>> @@ -300,6 +598,7 @@ long kvmppc_h_stuff_tce(struct kvm_vcpu *vcpu,
> >>>>>  {
> >>>>>  	struct kvmppc_spapr_tce_table *stt;
> >>>>>  	long i, ret;
> >>>>> +	struct kvmppc_spapr_tce_iommu_table *stit;
> >>>>>  
> >>>>>  	stt = kvmppc_find_table(vcpu->kvm, liobn);
> >>>>>  	if (!stt)
> >>>>> @@ -313,6 +612,24 @@ long kvmppc_h_stuff_tce(struct kvm_vcpu *vcpu,
> >>>>>  	if (tce_value & (TCE_PCI_WRITE | TCE_PCI_READ))
> >>>>>  		return H_PARAMETER;
> >>>>>  
> >>>>> +	list_for_each_entry_lockless(stit, &stt->iommu_tables, next) {
> >>>>> +		unsigned long entry = ioba >> stit->tbl->it_page_shift;
> >>>>> +
> >>>>> +		for (i = 0; i < npages; ++i) {
> >>>>> +			ret = kvmppc_tce_iommu_unmap(vcpu->kvm,
> >>>>> +					stit->tbl, entry + i);
> >>>>> +
> >>>>> +			if (ret == H_SUCCESS)
> >>>>> +				continue;
> >>>>> +
> >>>>> +			if (ret == H_TOO_HARD)
> >>>>> +				return ret;
> >>>>> +
> >>>>> +			WARN_ON_ONCE(1);
> >>>>> +			kvmppc_clear_tce(stit->tbl, entry);
> >>>>> +		}
> >>>>> +	}
> >>>>> +
> >>>>>  	for (i = 0; i < npages; ++i, ioba += (1ULL << stt->page_shift))
> >>>>>  		kvmppc_tce_put(stt, ioba >> stt->page_shift, tce_value);
> >>>>>  
> >>>>> diff --git a/arch/powerpc/kvm/book3s_64_vio_hv.c b/arch/powerpc/kvm/book3s_64_vio_hv.c
> >>>>> index 440d3ab5dc32..3ad06badc552 100644
> >>>>> --- a/arch/powerpc/kvm/book3s_64_vio_hv.c
> >>>>> +++ b/arch/powerpc/kvm/book3s_64_vio_hv.c
> >>>>> @@ -161,11 +161,108 @@ long kvmppc_gpa_to_ua(struct kvm *kvm, unsigned long gpa,
> >>>>>  EXPORT_SYMBOL_GPL(kvmppc_gpa_to_ua);
> >>>>>  
> >>>>>  #ifdef CONFIG_KVM_BOOK3S_HV_POSSIBLE
> >>>>> +static void kvmppc_rm_clear_tce(struct iommu_table *tbl, unsigned long entry)
> >>>>> +{
> >>>>> +	unsigned long hpa = 0;
> >>>>> +	enum dma_data_direction dir = DMA_NONE;
> >>>>> +
> >>>>> +	iommu_tce_xchg_rm(tbl, entry, &hpa, &dir);
> >>>>> +}
> >>>>> +
> >>>>> +static long kvmppc_rm_tce_iommu_mapped_dec(struct kvm *kvm,
> >>>>> +		struct iommu_table *tbl, unsigned long entry)
> >>>>> +{
> >>>>> +	struct mm_iommu_table_group_mem_t *mem = NULL;
> >>>>> +	const unsigned long pgsize = 1ULL << tbl->it_page_shift;
> >>>>> +	unsigned long *pua = IOMMU_TABLE_USERSPACE_ENTRY(tbl, entry);
> >>>>> +
> >>>>> +	if (WARN_ON_ONCE(!pua))
> >>>>> +		return H_HARDWARE;
> >>>>
> >>>> So.. I know I encouraged WARN_ON()s, but is it safe to call WARN_ON()
> >>>> from real mode?
> >>>
> >>> Ouch. Tried WARN_ON_ONCE(1) in kvmppc_rm_h_stuff_tce() and got "rcu_sched
> >>> detected stalls" straight away.
> >>
> >> Bother.  Sorry I didn't think of that earlier.
> >>
> >>> What do I replace it with, in documenting purposes?
> >>>
> >>> -	if (WARN_ON_ONCE(!pua))
> >>> +       if (!pua) /* Not expected to fail */
> >>
> >> So, I'd suggest adding a WARN_ON_RM() or whatever macro to wrap this
> >> at least.  As you may have seen I discussed this with mpe on IRC and
> >> printk() should work, so you could just put a printk() and
> >> dump_stack() in there.
> > 
> > Yes, noticed. Thanks!
> > 
> 
> Something like this? Copied from include/asm-generic/bug.h.

Assuming you've checked that pr_err(), dump_stack() and the section
reference work ok in real mode, that looks fine.

> 
> 
> diff --git a/arch/powerpc/kvm/book3s_64_vio_hv.c
> b/arch/powerpc/kvm/book3s_64_vio_hv.c
> index 3ad06badc552..9d6f7e2043ca 100644
> --- a/arch/powerpc/kvm/book3s_64_vio_hv.c
> +++ b/arch/powerpc/kvm/book3s_64_vio_hv.c
> @@ -40,6 +40,31 @@
>  #include <asm/iommu.h>
>  #include <asm/tce.h>
> 
> +#ifdef CONFIG_BUG
> +
> +#define WARN_ON_ONCE_RM(condition)     ({                      \
> +       static bool __section(.data.unlikely) __warned;         \
> +       int __ret_warn_once = !!(condition);                    \
> +                                                               \
> +       if (unlikely(__ret_warn_once && !__warned)) {           \
> +               __warned = true;                                \
> +               pr_err("WARN_ON_ONCE_RM: (%s) at %s:%u\n",      \
> +                               __stringify(condition),         \
> +                               __func__, __LINE__);            \
> +               dump_stack();                                   \
> +       }                                                       \
> +       unlikely(__ret_warn_once);                              \
> +})
> +
> +#else
> +
> +#define WARN_ON_ONCE_RM(condition) ({                          \
> +       int __ret_warn_on = !!(condition);                      \
> +       unlikely(__ret_warn_on);                                \
> +})
> +
> +#endif
> +
> 
> 
> 
> > 
> > 
> > 
> 
> 

-- 
David Gibson			| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you.  NOT _the_ _other_
				| _way_ _around_!
http://www.ozlabs.org/~dgibson