Re: [PATCH v5 15/19] iommufd: vfio container FD ioctl compatibility

Eric Auger
2022-11-28T20:54:27Z

On 11/28/22 20:37, Jason Gunthorpe wrote:
> On Mon, Nov 28, 2022 at 06:53:12PM +0100, Eric Auger wrote:
>
>>> +static int iommufd_vfio_map_dma(struct iommufd_ctx *ictx, unsigned int cmd,
>>> + void __user *arg)
>>> +{
>>> + u32 supported_flags = VFIO_DMA_MAP_FLAG_READ | VFIO_DMA_MAP_FLAG_WRITE;
>>> + size_t minsz = offsetofend(struct vfio_iommu_type1_dma_map, size);
>>> + struct vfio_iommu_type1_dma_map map;
>>> + int iommu_prot = IOMMU_CACHE;
>>> + struct iommufd_ioas *ioas;
>>> + unsigned long iova;
>>> + int rc;
>>> +
>>> + if (copy_from_user(&map, arg, minsz))
>>> + return -EFAULT;
>>> +
>>> + if (map.argsz < minsz || map.flags & ~supported_flags)
>>> + return -EINVAL;
>>> +
>>> + if (map.flags & VFIO_DMA_MAP_FLAG_READ)
>>> + iommu_prot |= IOMMU_READ;
>>> + if (map.flags & VFIO_DMA_MAP_FLAG_WRITE)
>>> + iommu_prot |= IOMMU_WRITE;
>>> +
>>> + ioas = get_compat_ioas(ictx);
>>> + if (IS_ERR(ioas))
>>> + return PTR_ERR(ioas);
>>> +
>>> + /*
>>> + * Maps created through the legacy interface always use VFIO compatible
>>> + * rlimit accounting. If the user wishes to use the faster user based
>>> + * rlimit accounting then they must use the new interface.
>> s/they/he
> "they" has become a common neutral singular pronoun in English.

Oh OK.
>
>>> +static int iommufd_vfio_unmap_dma(struct iommufd_ctx *ictx, unsigned int cmd,
>>> + void __user *arg)
>>> +{
>>> + size_t minsz = offsetofend(struct vfio_iommu_type1_dma_unmap, size);
>>> + /*
>>> + * VFIO_DMA_UNMAP_FLAG_GET_DIRTY_BITMAP is obsoleted by the new
>>> + * dirty tracking direction:
>>> + * https://lore.kernel.org/kvm/20220731125503.142683-1-yishaih@nvidia.com/
>>> + * https://lore.kernel.org/kvm/20220428210933.3583-1-joao.m.martins@oracle.com/
>>> + */
>>> + u32 supported_flags = VFIO_DMA_UNMAP_FLAG_ALL;
>>> + struct vfio_iommu_type1_dma_unmap unmap;
>>> + unsigned long unmapped = 0;
>>> + struct iommufd_ioas *ioas;
>>> + int rc;
>>> +
>>> + if (copy_from_user(&unmap, arg, minsz))
>>> + return -EFAULT;
>>> +
>>> + if (unmap.argsz < minsz || unmap.flags & ~supported_flags)
>>> + return -EINVAL;
>>> +
>>> + ioas = get_compat_ioas(ictx);
>>> + if (IS_ERR(ioas))
>>> + return PTR_ERR(ioas);
>>> +
>>> + if (unmap.flags & VFIO_DMA_UNMAP_FLAG_ALL) {
>>> + if (unmap.iova != 0 || unmap.size != 0) {
>>> + rc = -EINVAL;
>>> + goto err_put;
>>> + }
>>> + rc = iopt_unmap_all(&ioas->iopt, &unmapped);
>>> + } else {
>>> + if (READ_ONCE(ioas->iopt.disable_large_pages)) {
>>> + unsigned long iovas[] = { unmap.iova + unmap.size - 1,
>>> + unmap.iova - 1 };
>>> +
>>> + rc = iopt_cut_iova(&ioas->iopt, iovas,
>>> + unmap.iova ? 2 : 1);
>> please can you add a comment to explain what this is supposed to do?
> iova -1 when iova == 0 will underflow and becomes garbage
>
> /*
> * Create cuts at the start and last of the requested
> * range. If the start IOVA is 0 then it doesn't need to
> * be cut.
> */

OK thanks
>
>>> +static int iommufd_vfio_set_iommu(struct iommufd_ctx *ictx, unsigned long type)
>>> +{
>>> + struct iommufd_ioas *ioas = NULL;
>>> + int rc = 0;
>>> +
>>> + if (type != VFIO_TYPE1_IOMMU && type != VFIO_TYPE1v2_IOMMU)
>>> + return -EINVAL;
>>> +
>>> + /* VFIO fails the set_iommu if there is no group */
>>> + ioas = get_compat_ioas(ictx);
>>> + if (IS_ERR(ioas))
>>> + return PTR_ERR(ioas);
>>> + if (type == VFIO_TYPE1_IOMMU)
>>> + rc = iopt_disable_large_pages(&ioas->iopt);
>> please can you document/explain this setting?
> /*
> * The difference between TYPE1 and TYPE1v2 is the ability to unmap in
> * the middle of mapped ranges. This is complicated by huge page support
> * which creates single large IOPTEs that cannot be split by the iommu
> * driver. TYPE1 is very old at this point and likely nothing uses it,
> * however it is simple enough to emulate by simply disabling the
> * problematic large IOPTEs. Then we can safely unmap within any range.
OK makes sense. That's helpful

with those additions,
Reviewed-by: Eric Auger <eric.auger@redhat.com>

Eric

> */
>
> Thanks,
> Jason
>