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

2022-04-09 Thread Lu Baolu 

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 
---
  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 

Best regards,
baolu
___
iommu mailing list
iommu@lists.linux-foundation.org
https://lists.linuxfoundation.org/mailman/listinfo/iommu

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

2022-04-08 Thread Jason Gunthorpe via iommu 
On Fri, Apr 08, 2022 at 08:21:55AM +, Tian, Kevin wrote:
> (CC Jason Wang)
> 
> > From: Jason Gunthorpe
> > Sent: Thursday, April 7, 2022 11:24 PM
> > 
> > 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 
> 
> Reviewed-by: Kevin Tian 
> 
> btw the comment about vsnic and vdpa matches my thought. But
> a recent change in Qemu [1] possibly wants confirmation from
> Jason Wang.
> 
> [1] https://lore.kernel.org/all/20220304133556.233983-20-...@redhat.com/

That patch seems to have run into the confusion this series is
addressing.

VFIO_DMA_CC_IOMMU and snoop control is absolutely not needed by
VDPA. We expect the VDPA kernel driver to be well behaved and not
cause its device to generate no-snoop TLPs.

VDPA needs IOMMU_CACHE only.

Jason
___
iommu mailing list
iommu@lists.linux-foundation.org
https://lists.linuxfoundation.org/mailman/listinfo/iommu

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

2022-04-08 Thread Tian, Kevin 
(CC Jason Wang)

> From: Jason Gunthorpe
> Sent: Thursday, April 7, 2022 11:24 PM
> 
> 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 

Reviewed-by: Kevin Tian 

btw the comment about vsnic and vdpa matches my thought. But
a recent change in Qemu [1] possibly wants confirmation from
Jason Wang.

[1] https://lore.kernel.org/all/20220304133556.233983-20-...@redhat.com/

Thanks
Kevin
___
iommu mailing list
iommu@lists.linux-foundation.org
https://lists.linuxfoundation.org/mailman/listinfo/iommu

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

2022-04-07 Thread Jason Gunthorpe via iommu 
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 
---
 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

___
iommu mailing list
iommu@lists.linux-foundation.org
https://lists.linuxfoundation.org/mailman/listinfo/iommu