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Message-ID: <1446053858.8018.406.camel@redhat.com>
Date: Wed, 28 Oct 2015 11:37:38 -0600
From: Alex Williamson <alex.williamson@...hat.com>
To: Eric Auger <eric.auger@...aro.org>
Cc: eric.auger@...com, linux-arm-kernel@...ts.infradead.org,
kvmarm@...ts.cs.columbia.edu, kvm@...r.kernel.org,
will.deacon@....com, suravee.suthikulpanit@....com,
christoffer.dall@...aro.org, linux-kernel@...r.kernel.org,
patches@...aro.org
Subject: Re: [RFC] vfio/type1: handle case where IOMMU does not support
PAGE_SIZE size
On Wed, 2015-10-28 at 18:10 +0100, Eric Auger wrote:
> Hi Alex,
> On 10/28/2015 05:27 PM, Alex Williamson wrote:
> > On Wed, 2015-10-28 at 13:12 +0000, Eric Auger wrote:
> >> Current vfio_pgsize_bitmap code hides the supported IOMMU page
> >> sizes smaller than PAGE_SIZE. As a result, in case the IOMMU
> >> does not support PAGE_SIZE page, the alignment check on map/unmap
> >> is done with larger page sizes, if any. This can fail although
> >> mapping could be done with pages smaller than PAGE_SIZE.
> >>
> >> vfio_pgsize_bitmap is modified to expose the IOMMU page sizes,
> >> supported by all domains, even those smaller than PAGE_SIZE. The
> >> alignment check on map is performed against PAGE_SIZE if the minimum
> >> IOMMU size is less than PAGE_SIZE or against the min page size greater
> >> than PAGE_SIZE.
> >>
> >> Signed-off-by: Eric Auger <eric.auger@...aro.org>
> >>
> >> ---
> >>
> >> This was tested on AMD Seattle with 64kB page host. ARM MMU 401
> >> currently expose 4kB, 2MB and 1GB page support. With a 64kB page host,
> >> the map/unmap check is done against 2MB. Some alignment check fail
> >> so VFIO_IOMMU_MAP_DMA fail while we could map using 4kB IOMMU page
> >> size.
> >> ---
> >> drivers/vfio/vfio_iommu_type1.c | 25 +++++++++++--------------
> >> 1 file changed, 11 insertions(+), 14 deletions(-)
> >>
> >> diff --git a/drivers/vfio/vfio_iommu_type1.c b/drivers/vfio/vfio_iommu_type1.c
> >> index 57d8c37..13fb974 100644
> >> --- a/drivers/vfio/vfio_iommu_type1.c
> >> +++ b/drivers/vfio/vfio_iommu_type1.c
> >> @@ -403,7 +403,7 @@ static void vfio_remove_dma(struct vfio_iommu *iommu, struct vfio_dma *dma)
> >> static unsigned long vfio_pgsize_bitmap(struct vfio_iommu *iommu)
> >> {
> >> struct vfio_domain *domain;
> >> - unsigned long bitmap = PAGE_MASK;
> >> + unsigned long bitmap = ULONG_MAX;
> >
> > Isn't this and removing the WARN_ON()s the only real change in this
> > patch? The rest looks like conversion to use IS_ALIGNED and the
> > following test, that I don't really understand...
> Yes basically you're right.
Ok, so with hopefully correcting my understand of what this does, isn't
this effectively the same:
diff --git a/drivers/vfio/vfio_iommu_type1.c b/drivers/vfio/vfio_iommu_type1.c
index 57d8c37..7db4f5a 100644
--- a/drivers/vfio/vfio_iommu_type1.c
+++ b/drivers/vfio/vfio_iommu_type1.c
@@ -403,13 +403,19 @@ static void vfio_remove_dma(struct vfio_iommu *iommu, stru
static unsigned long vfio_pgsize_bitmap(struct vfio_iommu *iommu)
{
struct vfio_domain *domain;
- unsigned long bitmap = PAGE_MASK;
+ unsigned long bitmap = ULONG_MAX;
mutex_lock(&iommu->lock);
list_for_each_entry(domain, &iommu->domain_list, next)
bitmap &= domain->domain->ops->pgsize_bitmap;
mutex_unlock(&iommu->lock);
+ /* Some comment about how the IOMMU API splits requests */
+ if (bitmap & ~PAGE_MASK) {
+ bitmap &= PAGE_MASK;
+ bitmap |= PAGE_SIZE;
+ }
+
return bitmap;
}
This would also expose to the user that we're accepting PAGE_SIZE, which
we weren't before, so it was not quite right to just let them do it
anyway. I don't think we even need to get rid of the WARN_ONs, do we?
Thanks,
Alex
> >
> >>
> >> mutex_lock(&iommu->lock);
> >> list_for_each_entry(domain, &iommu->domain_list, next)
> >> @@ -416,20 +416,18 @@ static unsigned long vfio_pgsize_bitmap(struct vfio_iommu *iommu)
> >> static int vfio_dma_do_unmap(struct vfio_iommu *iommu,
> >> struct vfio_iommu_type1_dma_unmap *unmap)
> >> {
> >> - uint64_t mask;
> >> struct vfio_dma *dma;
> >> size_t unmapped = 0;
> >> int ret = 0;
> >> + unsigned int min_pagesz = __ffs(vfio_pgsize_bitmap(iommu));
> >> + unsigned int requested_alignment = (min_pagesz < PAGE_SIZE) ?
> >> + PAGE_SIZE : min_pagesz;
> >
> > This one. If we're going to support sub-PAGE_SIZE mappings, why do we
> > care to cap alignment at PAGE_SIZE?
> My intent in this patch isn't to allow the user-space to map/unmap
> sub-PAGE_SIZE buffers. The new test makes sure the mapped area is bigger
> or equal than a host page whatever the supported page sizes.
>
> I noticed that chunk construction, pinning and other many things are
> based on PAGE_SIZE and far be it from me to change that code! I want to
> keep that minimal granularity for all those computation.
>
> However on iommu side, I would like to rely on the fact the iommu driver
> is clever enough to choose the right page size and even to choose a size
> that is smaller than PAGE_SIZE if this latter is not supported.
> >
> >> - mask = ((uint64_t)1 << __ffs(vfio_pgsize_bitmap(iommu))) - 1;
> >> -
> >> - if (unmap->iova & mask)
> >> + if (!IS_ALIGNED(unmap->iova, requested_alignment))
> >> return -EINVAL;
> >> - if (!unmap->size || unmap->size & mask)
> >> + if (!unmap->size || !IS_ALIGNED(unmap->size, requested_alignment))
> >> return -EINVAL;
> >>
> >> - WARN_ON(mask & PAGE_MASK);
> >> -
> >> mutex_lock(&iommu->lock);
> >>
> >> /*
> >> @@ -553,25 +551,24 @@ static int vfio_dma_do_map(struct vfio_iommu *iommu,
> >> size_t size = map->size;
> >> long npage;
> >> int ret = 0, prot = 0;
> >> - uint64_t mask;
> >> struct vfio_dma *dma;
> >> unsigned long pfn;
> >> + unsigned int min_pagesz = __ffs(vfio_pgsize_bitmap(iommu));
> >> + unsigned int requested_alignment = (min_pagesz < PAGE_SIZE) ?
> >> + PAGE_SIZE : min_pagesz;
> >>
> >> /* Verify that none of our __u64 fields overflow */
> >> if (map->size != size || map->vaddr != vaddr || map->iova != iova)
> >> return -EINVAL;
> >>
> >> - mask = ((uint64_t)1 << __ffs(vfio_pgsize_bitmap(iommu))) - 1;
> >> -
> >> - WARN_ON(mask & PAGE_MASK);
> >> -
> >> /* READ/WRITE from device perspective */
> >> if (map->flags & VFIO_DMA_MAP_FLAG_WRITE)
> >> prot |= IOMMU_WRITE;
> >> if (map->flags & VFIO_DMA_MAP_FLAG_READ)
> >> prot |= IOMMU_READ;
> >>
> >> - if (!prot || !size || (size | iova | vaddr) & mask)
> >> + if (!prot || !size ||
> >> + !IS_ALIGNED(size | iova | vaddr, requested_alignment))
> >> return -EINVAL;
> >>
> >> /* Don't allow IOVA or virtual address wrap */
> >
> > This is mostly ignoring the problems with sub-PAGE_SIZE mappings. For
> > instance, we can only pin on PAGE_SIZE and therefore we only do
> > accounting on PAGE_SIZE, so if the user does 4K mappings across your 64K
> > page, that page gets pinned and accounted 16 times. Are we going to
> > tell users that their locked memory limit needs to be 16x now? The rest
> > of the code would need an audit as well to see what other sub-page bugs
> > might be hiding. Thanks,
> So if the user is not allowed to map sub-PAGE_SIZE buffers, accounting
> still is based on PAGE_SIZE while iommu mapping can be based on
> sub-PAGE_SIZE pages. I am misunderstanding something?
>
> Best Regards
>
> Eric
> >
> > Alex
> >
> >
> >
>
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