Re: [PATCH v1 7/8] vfio/type1: Add VFIO_IOMMU_CACHE_INVALIDATE

Jacob Pan
2020-04-03T15:26:01Z

On Fri, 3 Apr 2020 06:39:22 +0000
"Tian, Kevin" <kevin.tian@intel.com> wrote:

> > From: Alex Williamson <alex.williamson@redhat.com>
> > Sent: Friday, April 3, 2020 4:24 AM
> >
> > On Sun, 22 Mar 2020 05:32:04 -0700
> > "Liu, Yi L" <yi.l.liu@intel.com> wrote:
> >
> > > From: Liu Yi L <yi.l.liu@linux.intel.com>
> > >
> > > For VFIO IOMMUs with the type VFIO_TYPE1_NESTING_IOMMU, guest
> > "owns" the
> > > first-level/stage-1 translation structures, the host IOMMU driver
> > > has no knowledge of first-level/stage-1 structure cache updates
> > > unless the guest invalidation requests are trapped and propagated
> > > to the host.
> > >
> > > This patch adds a new IOCTL VFIO_IOMMU_CACHE_INVALIDATE to
> > propagate guest
> > > first-level/stage-1 IOMMU cache invalidations to host to ensure
> > > IOMMU
> > cache
> > > correctness.
> > >
> > > With this patch, vSVA (Virtual Shared Virtual Addressing) can be
> > > used safely as the host IOMMU iotlb correctness are ensured.
> > >
> > > Cc: Kevin Tian <kevin.tian@intel.com>
> > > CC: Jacob Pan <jacob.jun.pan@linux.intel.com>
> > > Cc: Alex Williamson <alex.williamson@redhat.com>
> > > Cc: Eric Auger <eric.auger@redhat.com>
> > > Cc: Jean-Philippe Brucker <jean-philippe@linaro.org>
> > > Signed-off-by: Liu Yi L <yi.l.liu@linux.intel.com>
> > > Signed-off-by: Eric Auger <eric.auger@redhat.com>
> > > Signed-off-by: Jacob Pan <jacob.jun.pan@linux.intel.com>
> > > ---
> > > drivers/vfio/vfio_iommu_type1.c | 49
> > +++++++++++++++++++++++++++++++++++++++++
> > > include/uapi/linux/vfio.h | 22 ++++++++++++++++++
> > > 2 files changed, 71 insertions(+)
> > >
> > > diff --git a/drivers/vfio/vfio_iommu_type1.c
> > b/drivers/vfio/vfio_iommu_type1.c
> > > index a877747..937ec3f 100644
> > > --- a/drivers/vfio/vfio_iommu_type1.c
> > > +++ b/drivers/vfio/vfio_iommu_type1.c
> > > @@ -2423,6 +2423,15 @@ static long
> > vfio_iommu_type1_unbind_gpasid(struct vfio_iommu *iommu,
> > > return ret;
> > > }
> > >
> > > +static int vfio_cache_inv_fn(struct device *dev, void *data)
> > > +{
> > > + struct domain_capsule *dc = (struct domain_capsule
> > > *)data;
> > > + struct iommu_cache_invalidate_info *cache_inv_info =
> > > + (struct iommu_cache_invalidate_info *) dc->data;
> > > +
> > > + return iommu_cache_invalidate(dc->domain, dev,
> > > cache_inv_info); +}
> > > +
> > > static long vfio_iommu_type1_ioctl(void *iommu_data,
> > > unsigned int cmd, unsigned
> > > long arg) {
> > > @@ -2629,6 +2638,46 @@ static long vfio_iommu_type1_ioctl(void
> > *iommu_data,
> > > }
> > > kfree(gbind_data);
> > > return ret;
> > > + } else if (cmd == VFIO_IOMMU_CACHE_INVALIDATE) {
> > > + struct vfio_iommu_type1_cache_invalidate
> > > cache_inv;
> > > + u32 version;
> > > + int info_size;
> > > + void *cache_info;
> > > + int ret;
> > > +
> > > + minsz = offsetofend(struct
> > vfio_iommu_type1_cache_invalidate,
> > > + flags);
> >
> > This breaks backward compatibility as soon as struct
> > iommu_cache_invalidate_info changes size by its defined versioning
> > scheme. ie. a field gets added, the version is bumped, all existing
> > userspace breaks. Our minsz is offsetofend to the version field,
> > interpret the version to size, then reevaluate argsz.
>
> btw the version scheme is challenged by Christoph Hellwig. After
> some discussions, we need your guidance how to move forward.
> Jacob summarized available options below:
> https://lkml.org/lkml/2020/4/2/876
>
For this particular case, I don't quite get the difference between
minsz=flags and minsz=version. Our IOMMU version scheme will only
change size at the end where the variable union is used for vendor
specific extensions. Version bump does not change size (only re-purpose
padding) from the start of the UAPI structure to the union, i.e. version
will __always__ be after struct vfio_iommu_type1_cache_invalidate.flags.

> >
> > > +
> > > + if (copy_from_user(&cache_inv, (void __user
> > > *)arg, minsz))
> > > + return -EFAULT;
> > > +
> > > + if (cache_inv.argsz < minsz || cache_inv.flags)
> > > + return -EINVAL;
> > > +
> > > + /* Get the version of struct
> > > iommu_cache_invalidate_info */
> > > + if (copy_from_user(&version,
> > > + (void __user *) (arg + minsz),
> > > sizeof(version)))
> > > + return -EFAULT;
> > > +
> > > + info_size = iommu_uapi_get_data_size(
> > > + IOMMU_UAPI_CACHE_INVAL,
> > version);
> > > +
> > > + cache_info = kzalloc(info_size, GFP_KERNEL);
> > > + if (!cache_info)
> > > + return -ENOMEM;
> > > +
> > > + if (copy_from_user(cache_info,
> > > + (void __user *) (arg + minsz),
> > > info_size)) {
> > > + kfree(cache_info);
> > > + return -EFAULT;
> > > + }
> > > +
> > > + mutex_lock(&iommu->lock);
> > > + ret = vfio_iommu_for_each_dev(iommu,
> > > vfio_cache_inv_fn,
> > > + cache_info);
> >
> > How does a user respond when their cache invalidate fails? Isn't
> > this also another case where our for_each_dev can fail at an
> > arbitrary point leaving us with no idea whether each device even
> > had the opportunity to perform the invalidation request. I don't
> > see how we have any chance to maintain coherency after this
> > faults.
>
> Then can we make it simple to support singleton group only?
>
> >
> > > + mutex_unlock(&iommu->lock);
> > > + kfree(cache_info);
> > > + return ret;
> > > }
> > >
> > > return -ENOTTY;
> > > diff --git a/include/uapi/linux/vfio.h b/include/uapi/linux/vfio.h
> > > index 2235bc6..62ca791 100644
> > > --- a/include/uapi/linux/vfio.h
> > > +++ b/include/uapi/linux/vfio.h
> > > @@ -899,6 +899,28 @@ struct vfio_iommu_type1_bind {
> > > */
> > > #define VFIO_IOMMU_BIND _IO(VFIO_TYPE, VFIO_BASE
> > > + 23)
> > >
> > > +/**
> > > + * VFIO_IOMMU_CACHE_INVALIDATE - _IOW(VFIO_TYPE, VFIO_BASE + 24,
> > > + * struct
> > > vfio_iommu_type1_cache_invalidate)
> > > + *
> > > + * Propagate guest IOMMU cache invalidation to the host. The
> > > cache
> > > + * invalidation information is conveyed by @cache_info, the
> > > content
> > > + * format would be structures defined in uapi/linux/iommu.h. User
> > > + * should be aware of that the struct
> > > iommu_cache_invalidate_info
> > > + * has a @version field, vfio needs to parse this field before
> > > getting
> > > + * data from userspace.
> > > + *
> > > + * Availability of this IOCTL is after VFIO_SET_IOMMU.
> >
> > Is this a necessary qualifier? A user can try to call this ioctl at
> > any point, it only makes sense in certain configurations, but it
> > should always "do the right thing" relative to the container iommu
> > config.
> >
> > Also, I don't see anything in these last few patches testing the
> > operating IOMMU model, what happens when a user calls them when not
> > using the nesting IOMMU?
> >
> > Is this ioctl and the previous BIND ioctl only valid when configured
> > for the nesting IOMMU type?
>
> I think so. We should add the nesting check in those new ioctls.
>
I also added nesting domain attribute check in IOMMU driver, so bind
guest PASID will fail if nesting mode is not supported. There will be
no invalidation w/o bind.

> >
> > > + *
> > > + * returns: 0 on success, -errno on failure.
> > > + */
> > > +struct vfio_iommu_type1_cache_invalidate {
> > > + __u32 argsz;
> > > + __u32 flags;
> > > + struct iommu_cache_invalidate_info cache_info;
> > > +};
> > > +#define VFIO_IOMMU_CACHE_INVALIDATE _IO(VFIO_TYPE,
> > > VFIO_BASE
> > + 24)
> >
> > The future extension capabilities of this ioctl worry me, I wonder
> > if we should do another data[] with flag defining that data as
> > CACHE_INFO.
>
> Can you elaborate? Does it mean with this way we don't rely on iommu
> driver to provide version_to_size conversion and instead we just pass
> data[] to iommu driver for further audit?
>
I guess Alex meant we do something similar to:
struct vfio_irq_set {
__u32 argsz;
__u32 flags;
#define VFIO_IRQ_SET_DATA_NONE (1 << 0) /* Data not present */
#define VFIO_IRQ_SET_DATA_BOOL (1 << 1) /* Data is bool (u8) */
#define VFIO_IRQ_SET_DATA_EVENTFD (1 << 2) /* Data is eventfd (s32) */
#define VFIO_IRQ_SET_ACTION_MASK (1 << 3) /* Mask interrupt */
#define VFIO_IRQ_SET_ACTION_UNMASK (1 << 4) /* Unmask interrupt */
#define VFIO_IRQ_SET_ACTION_TRIGGER (1 << 5) /* Trigger interrupt */
__u32 index;
__u32 start;
__u32 count;
__u8 data[];
};

So we could do:
struct vfio_iommu_type1_cache_invalidate {
__u32 argsz;
#define VFIO_INVL_DATA_NONE
#define VFIO_INVL_DATA_CACHE_INFO (1 << 1)
__u32 flags;
__u8 data[];
}

We still need version_to_size version, but under
if (flag & VFIO_INVL_DATA_CACHE_INFO)
get_size_from_version();

> >
> > > +
> > > /* -------- Additional API for SPAPR TCE (Server POWERPC) IOMMU
> > > --------
> > */
> > >
> > > /*
>
> Thanks
> Kevin

[Jacob Pan]