Subject: Re: [PATCH kernel 9/9] KVM: PPC: VFIO device: support SPAPR TCE

From: Alexey Kardashevskiy <[email-masked]>
Date: Fri, 11 Mar 2016 10:09:50 +1100

On 03/10/2016 04:21 PM, David Gibson wrote:
> On Wed, Mar 09, 2016 at 08:20:12PM +1100, Alexey Kardashevskiy wrote:
>> On 03/09/2016 04:45 PM, David Gibson wrote:
>>> On Mon, Mar 07, 2016 at 02:41:17PM +1100, Alexey Kardashevskiy wrote:
>>>> sPAPR TCE IOMMU is para-virtualized and the guest does map/unmap
>>>> via hypercalls which take a logical bus id (LIOBN) as a target IOMMU
>>>> identifier. LIOBNs are made up, advertised to guest systems and
>>>> linked to IOMMU groups by the user space.
>>>> In order to enable acceleration for IOMMU operations in KVM, we need
>>>> to tell KVM the information about the LIOBN-to-group mapping.
>>>>
>>>> For that, a new KVM_DEV_VFIO_GROUP_SET_SPAPR_TCE_LIOBN parameter
>>>> is added which accepts:
>>>> - a VFIO group fd and IO base address to find the actual hardware
>>>> TCE table;
>>>> - a LIOBN to assign to the found table.
>>>>
>>>> Before notifying KVM about new link, this check the group for being
>>>> registered with KVM device in order to release them at unexpected KVM
>>>> finish.
>>>>
>>>> This advertises the new KVM_CAP_SPAPR_TCE_VFIO capability to the user
>>>> space.
>>>>
>>>> While we are here, this also fixes VFIO KVM device compiling to let it
>>>> link to a KVM module.
>>>>
>>>> Signed-off-by: Alexey Kardashevskiy <[email-masked]>
>>>> ---
>>>>   Documentation/virtual/kvm/devices/vfio.txt |  21 +++++-
>>>>   arch/powerpc/kvm/Kconfig                   |   1 +
>>>>   arch/powerpc/kvm/Makefile                  |   5 +-
>>>>   arch/powerpc/kvm/powerpc.c                 |   1 +
>>>>   include/uapi/linux/kvm.h                   |   9 +++
>>>>   virt/kvm/vfio.c                            | 106 +++++++++++++++++++++++++++++
>>>>   6 files changed, 140 insertions(+), 3 deletions(-)
>>>>
>>>> diff --git a/Documentation/virtual/kvm/devices/vfio.txt b/Documentation/virtual/kvm/devices/vfio.txt
>>>> index ef51740..c0d3eb7 100644
>>>> --- a/Documentation/virtual/kvm/devices/vfio.txt
>>>> +++ b/Documentation/virtual/kvm/devices/vfio.txt
>>>> @@ -16,7 +16,24 @@ 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.
>>>
>>> AFAICT these changes are accurate for VFIO as it is already, in which
>>> case it might be clearer to put them in a separate patch.
>>>
>>>>     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.
>>>>
>>>> -For each, kvm_device_attr.addr points to an int32_t file descriptor
>>>> -for the VFIO group.
>>>> +  KVM_DEV_VFIO_GROUP_SET_SPAPR_TCE_LIOBN: sets a liobn for a VFIO group
>>>> +	kvm_device_attr.addr points to a struct:
>>>> +		struct kvm_vfio_spapr_tce_liobn {
>>>> +			__u32	argsz;
>>>> +			__s32	fd;
>>>> +			__u32	liobn;
>>>> +			__u8	pad[4];
>>>> +			__u64	start_addr;
>>>> +		};
>>>> +		where
>>>> +		@argsz is the size of kvm_vfio_spapr_tce_liobn;
>>>> +		@fd is a file descriptor for a VFIO group;
>>>> +		@liobn is a logical bus id to be associated with the group;
>>>> +		@start_addr is a DMA window offset on the IO (PCI) bus
>>>
>>> For the cause of DDW and multiple windows, I'm assuming you can call
>>> this multiple times with different LIOBNs and the same IOMMU group?
>>
>>
>> Yes. It is called twice per each group (when DDW is activated) - for 32bit
>> and 64bit windows, this is why @start_addr is there.
>>
>>
>>>> diff --git a/arch/powerpc/kvm/Kconfig b/arch/powerpc/kvm/Kconfig
>>>> index 1059846..dfa3488 100644
>>>> --- a/arch/powerpc/kvm/Kconfig
>>>> +++ b/arch/powerpc/kvm/Kconfig
>>>> @@ -65,6 +65,7 @@ config KVM_BOOK3S_64
>>>>   	select KVM
>>>>   	select KVM_BOOK3S_PR_POSSIBLE if !KVM_BOOK3S_HV_POSSIBLE
>>>>   	select SPAPR_TCE_IOMMU if IOMMU_SUPPORT
>>>> +	select KVM_VFIO if VFIO
>>>>   	---help---
>>>>   	  Support running unmodified book3s_64 and book3s_32 guest kernels
>>>>   	  in virtual machines on book3s_64 host processors.
>>>> diff --git a/arch/powerpc/kvm/Makefile b/arch/powerpc/kvm/Makefile
>>>> index 7f7b6d8..71f577c 100644
>>>> --- a/arch/powerpc/kvm/Makefile
>>>> +++ b/arch/powerpc/kvm/Makefile
>>>> @@ -8,7 +8,7 @@ ccflags-y := -Ivirt/kvm -Iarch/powerpc/kvm
>>>>   KVM := ../../../virt/kvm
>>>>
>>>>   common-objs-y = $(KVM)/kvm_main.o $(KVM)/coalesced_mmio.o \
>>>> -		$(KVM)/eventfd.o $(KVM)/vfio.o
>>>> +		$(KVM)/eventfd.o
>>>
>>> Please don't disable the VFIO device for the non-book3s case.  I added
>>> it (even though it didn't do anything until now) so that libvirt
>>> wouldn't choke when it finds it's not available.  Obviously the new
>>> ioctl needs to be only for the right IOMMU setup, but the device
>>> itself should be available always.
>>
>> Ah. Ok, I'll fix this. I just wanted to be able to compile kvm as a module.
>>
>>
>>>>   CFLAGS_e500_mmu.o := -I.
>>>>   CFLAGS_e500_mmu_host.o := -I.
>>>> @@ -87,6 +87,9 @@ endif
>>>>   kvm-book3s_64-objs-$(CONFIG_KVM_XICS) += \
>>>>   	book3s_xics.o
>>>>
>>>> +kvm-book3s_64-objs-$(CONFIG_KVM_VFIO) += \
>>>> +	$(KVM)/vfio.o \
>>>> +
>>>>   kvm-book3s_64-module-objs += \
>>>>   	$(KVM)/kvm_main.o \
>>>>   	$(KVM)/eventfd.o \
>>>> diff --git a/arch/powerpc/kvm/powerpc.c b/arch/powerpc/kvm/powerpc.c
>>>> index 19aa59b..63f188d 100644
>>>> --- a/arch/powerpc/kvm/powerpc.c
>>>> +++ b/arch/powerpc/kvm/powerpc.c
>>>> @@ -521,6 +521,7 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
>>>>   #ifdef CONFIG_PPC_BOOK3S_64
>>>>   	case KVM_CAP_SPAPR_TCE:
>>>>   	case KVM_CAP_SPAPR_TCE_64:
>>>> +	case KVM_CAP_SPAPR_TCE_VFIO:
>>>>   	case KVM_CAP_PPC_ALLOC_HTAB:
>>>>   	case KVM_CAP_PPC_RTAS:
>>>>   	case KVM_CAP_PPC_FIXUP_HCALL:
>>>> diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
>>>> index 080ffbf..f1abbea 100644
>>>> --- a/include/uapi/linux/kvm.h
>>>> +++ b/include/uapi/linux/kvm.h
>>>> @@ -1056,6 +1056,7 @@ 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_LIOBN	3
>>>>
>>>>   enum kvm_device_type {
>>>>   	KVM_DEV_TYPE_FSL_MPIC_20	= 1,
>>>> @@ -1075,6 +1076,14 @@ enum kvm_device_type {
>>>>   	KVM_DEV_TYPE_MAX,
>>>>   };
>>>>
>>>> +struct kvm_vfio_spapr_tce_liobn {
>>>> +	__u32	argsz;
>>>> +	__s32	fd;
>>>> +	__u32	liobn;
>>>> +	__u8	pad[4];
>>>> +	__u64	start_addr;
>>>> +};
>>>> +
>>>>   /*
>>>>    * ioctls for VM fds
>>>>    */
>>>> diff --git a/virt/kvm/vfio.c b/virt/kvm/vfio.c
>>>> index 1dd087d..87c771e 100644
>>>> --- a/virt/kvm/vfio.c
>>>> +++ b/virt/kvm/vfio.c
>>>> @@ -20,6 +20,10 @@
>>>>   #include <linux/vfio.h>
>>>>   #include "vfio.h"
>>>>
>>>> +#ifdef CONFIG_SPAPR_TCE_IOMMU
>>>> +#include <asm/kvm_ppc.h>
>>>> +#endif
>>>> +
>>>>   struct kvm_vfio_group {
>>>>   	struct list_head node;
>>>>   	struct vfio_group *vfio_group;
>>>> @@ -60,6 +64,22 @@ static void kvm_vfio_group_put_external_user(struct vfio_group *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;
>>>
>>> Should this be -ESOMETHING?
>>>
>>>> +	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 bool kvm_vfio_group_is_coherent(struct vfio_group *vfio_group)
>>>>   {
>>>>   	long (*fn)(struct vfio_group *, unsigned long);
>>>> @@ -110,6 +130,22 @@ static void kvm_vfio_update_coherency(struct kvm_device *dev)
>>>>   	mutex_unlock(&kv->lock);
>>>>   }
>>>>
>>>> +#ifdef CONFIG_SPAPR_TCE_IOMMU
>>>> +static void kvm_vfio_spapr_detach_iommu_group(struct kvm *kvm,
>>>> +		struct vfio_group *vfio_group)
>>>
>>>
>>> Shouldn't this go in the same patch that introduced the attach
>>> function?
>>
>> Having less patches which touch different maintainers areas is better. I
>> cannot avoid touching both PPC KVM and VFIO in this patch but I can in
>> "[PATCH kernel 6/9] KVM: PPC: Associate IOMMU group with guest view of TCE
>> table".
>>
>>
>>>
>>>> +{
>>>> +	int group_id;
>>>> +	struct iommu_group *grp;
>>>> +
>>>> +	group_id = kvm_vfio_external_user_iommu_id(vfio_group);
>>>> +	grp = iommu_group_get_by_id(group_id);
>>>> +	if (grp) {
>>>> +		kvm_spapr_tce_detach_iommu_group(kvm, grp);
>>>> +		iommu_group_put(grp);
>>>> +	}
>>>> +}
>>>> +#endif
>>>> +
>>>>   static int kvm_vfio_set_group(struct kvm_device *dev, long attr, u64 arg)
>>>>   {
>>>>   	struct kvm_vfio *kv = dev->private;
>>>> @@ -186,6 +222,10 @@ static int kvm_vfio_set_group(struct kvm_device *dev, long attr, u64 arg)
>>>>   				continue;
>>>>
>>>>   			list_del(&kvg->node);
>>>> +#ifdef CONFIG_SPAPR_TCE_IOMMU
>>>
>>> Better to make a no-op version of the call than have to #ifdef at the
>>> callsite.
>>
>> It is questionable. A x86 reader may decide that
>> KVM_DEV_VFIO_GROUP_SET_SPAPR_TCE_LIOBN is implemented for x86 and get
>> confused.
>>
>>
>>>
>>>> +			kvm_vfio_spapr_detach_iommu_group(dev->kvm,
>>>> +					kvg->vfio_group);
>>>> +#endif
>>>>   			kvm_vfio_group_put_external_user(kvg->vfio_group);
>>>>   			kfree(kvg);
>>>>   			ret = 0;
>>>> @@ -201,6 +241,69 @@ static int kvm_vfio_set_group(struct kvm_device *dev, long attr, u64 arg)
>>>>   		kvm_vfio_update_coherency(dev);
>>>>
>>>>   		return ret;
>>>> +
>>>> +#ifdef CONFIG_SPAPR_TCE_IOMMU
>>>> +	case KVM_DEV_VFIO_GROUP_SET_SPAPR_TCE_LIOBN: {
>>>> +		struct kvm_vfio_spapr_tce_liobn param;
>>>> +		unsigned long minsz;
>>>> +		struct kvm_vfio *kv = dev->private;
>>>> +		struct vfio_group *vfio_group;
>>>> +		struct kvm_vfio_group *kvg;
>>>> +		struct fd f;
>>>> +
>>>> +		minsz = offsetofend(struct kvm_vfio_spapr_tce_liobn,
>>>> +				start_addr);
>>>> +
>>>> +		if (copy_from_user(&param, (void __user *)arg, minsz))
>>>> +			return -EFAULT;
>>>> +
>>>> +		if (param.argsz < minsz)
>>>> +			return -EINVAL;
>>>> +
>>>> +		f = fdget(param.fd);
>>>> +		if (!f.file)
>>>> +			return -EBADF;
>>>> +
>>>> +		vfio_group = kvm_vfio_group_get_external_user(f.file);
>>>> +		fdput(f);
>>>> +
>>>> +		if (IS_ERR(vfio_group))
>>>> +			return PTR_ERR(vfio_group);
>>>> +
>>>> +		ret = -ENOENT;
>>>
>>> Shouldn't there be some runtime test for the type of the IOMMU?  It's
>>> possible a kernel could be built for a platform supporting multiple
>>> IOMMU types.
>>
>> Well, may make sense but I do not know to test that. The IOMMU type is a
>> VFIO container property, not a group property and here (KVM) we only have
>> groups.
>
> Which, as mentioned previously, is broken.

Which I am failing to follow you on this.

What I am trying to achieve here is pretty much referencing a group so it 
cannot be reused. Plus LIOBNs. Passing a container fd does not make much 
sense here as the VFIO device would walk through groups, reference them and 
that is it, there is no locking on VFIO containters and so far there was no 
need to teach KVM about containers.

What do I miss now?

>
>> And calling  iommu_group_get_iommudata() is quite useless as it returns a
>> void pointer... I could probably check that the release() callback is the
>> one I set via iommu_group_set_iommudata() but there is no API to get it from
>> a group.
>>
>> And I cannot really imagine a kernel with CONFIG_PPC_BOOK3S_64 (and
>> therefore KVM_CAP_SPAPR_TCE_VFIO enabled) with different IOMMU types. Can
>> the same kernel binary image work on both BOOK3S and embedded PPC? Where
>> these other types can come from?
>>
>>
>>>
>>>> +		mutex_lock(&kv->lock);
>>>> +
>>>> +		list_for_each_entry(kvg, &kv->group_list, node) {
>>>> +			int group_id;
>>>> +			struct iommu_group *grp;
>>>> +
>>>> +			if (kvg->vfio_group != vfio_group)
>>>> +				continue;
>>>> +
>>>> +			group_id = kvm_vfio_external_user_iommu_id(
>>>> +					kvg->vfio_group);
>>>> +			grp = iommu_group_get_by_id(group_id);
>>>> +			if (!grp) {
>>>> +				ret = -EFAULT;
>>>> +				break;
>>>> +			}
>>>> +
>>>> +			ret = kvm_spapr_tce_attach_iommu_group(dev->kvm,
>>>> +					param.liobn, param.start_addr,
>>>> +					grp);
>>>> +			if (ret)
>>>> +				iommu_group_put(grp);
>>>> +			break;
>>>> +		}
>>>> +
>>>> +		mutex_unlock(&kv->lock);
>>>> +
>>>> +		kvm_vfio_group_put_external_user(vfio_group);
>>>> +
>>>> +		return ret;
>>>> +	}
>>>> +#endif /* CONFIG_SPAPR_TCE_IOMMU */
>>>>   	}
>>>>
>>>>   	return -ENXIO;
>>>> @@ -225,6 +328,9 @@ static int kvm_vfio_has_attr(struct kvm_device *dev,
>>>>   		switch (attr->attr) {
>>>>   		case KVM_DEV_VFIO_GROUP_ADD:
>>>>   		case KVM_DEV_VFIO_GROUP_DEL:
>>>> +#ifdef CONFIG_SPAPR_TCE_IOMMU
>>>> +		case KVM_DEV_VFIO_GROUP_SET_SPAPR_TCE_LIOBN:
>>>> +#endif
>>>>   			return 0;
>>>>   		}
>>>>
>>>
>>
>>
>

-- 
Alexey