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Message-ID: <563101A0.7020404@linaro.org>
Date: Wed, 28 Oct 2015 18:10:56 +0100
From: Eric Auger <eric.auger@...aro.org>
To: Alex Williamson <alex.williamson@...hat.com>
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
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.
>
>>
>> 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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