Hi Will,
On 10/28/2015 06:14 PM, Will Deacon wrote:
> On Wed, Oct 28, 2015 at 10:27:28AM -0600, Alex Williamson wrote:
>> On Wed, 2015-10-28 at 13:12 +0000, Eric Auger wrote:
>>> 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...
>>
>>>
>>> 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?
>
> Eric can clarify, but I think the intention here is to have VFIO continue
> doing things in PAGE_SIZE chunks precisely so that we don't have to rework
> all of the pinning code etc.
That's my intention indeed ;-)
Thanks
Eric
The IOMMU API can then deal with the smaller
> page size.
>
>>> - 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,
>
> I don't see that. The pinning all happens the same in VFIO, which can
> then happily pass a 64k region to iommu_map. iommu_map will then call
> ->map in 4k chunks on the IOMMU driver ops.
>
> Will
>
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