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

Jason Gunthorpe
2022-04-07T15:24:02Z

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 */
};
--
2.35.1