Re: [PATCH v2 3/4] iommu: Redefine IOMMU_CAP_CACHE_COHERENCY as the cap flag for IOMMU_CACHE

Lu Baolu
2022-04-09T12:51:55Z

On 2022/4/7 23:23, Jason Gunthorpe wrote:
> While the comment was correct that this flag was intended to convey the
> block no-snoop support in the IOMMU, it has become widely implemented and
> used to mean the IOMMU supports IOMMU_CACHE as a map flag. Only the Intel
> driver was different.
>
> Now that the Intel driver is using enforce_cache_coherency() update the
> comment to make it clear that IOMMU_CAP_CACHE_COHERENCY is only about
> IOMMU_CACHE. Fix the Intel driver to return true since IOMMU_CACHE always
> works.
>
> The two places that test this flag, usnic and vdpa, are both assigning
> userspace pages to a driver controlled iommu_domain and require
> IOMMU_CACHE behavior as they offer no way for userspace to synchronize
> caches.
>
> Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>
> ---
> drivers/iommu/intel/iommu.c | 2 +-
> include/linux/iommu.h | 3 +--
> 2 files changed, 2 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/iommu/intel/iommu.c b/drivers/iommu/intel/iommu.c
> index 8f3674e997df06..14ba185175e9ec 100644
> --- a/drivers/iommu/intel/iommu.c
> +++ b/drivers/iommu/intel/iommu.c
> @@ -4556,7 +4556,7 @@ static bool intel_iommu_enforce_cache_coherency(struct iommu_domain *domain)
> static bool intel_iommu_capable(enum iommu_cap cap)
> {
> if (cap == IOMMU_CAP_CACHE_COHERENCY)
> - return domain_update_iommu_snooping(NULL);
> + return true;
> if (cap == IOMMU_CAP_INTR_REMAP)
> return irq_remapping_enabled == 1;
>
> diff --git a/include/linux/iommu.h b/include/linux/iommu.h
> index fe4f24c469c373..fd58f7adc52796 100644
> --- a/include/linux/iommu.h
> +++ b/include/linux/iommu.h
> @@ -103,8 +103,7 @@ static inline bool iommu_is_dma_domain(struct iommu_domain *domain)
> }
>
> enum iommu_cap {
> - IOMMU_CAP_CACHE_COHERENCY, /* IOMMU can enforce cache coherent DMA
> - transactions */
> + IOMMU_CAP_CACHE_COHERENCY, /* IOMMU_CACHE is supported */
> IOMMU_CAP_INTR_REMAP, /* IOMMU supports interrupt isolation */
> IOMMU_CAP_NOEXEC, /* IOMMU_NOEXEC flag */
> };

Reviewed-by: Lu Baolu <baolu.lu@linux.intel.com>

Best regards,
baolu