Messages in this thread | | | From | "Tian, Kevin" <> | Subject | RE: [PATCH v2 1/4] iommu/vt-d: Check before setting PGSNP bit in pasid table entry | Date | Sun, 24 Apr 2022 03:37:48 +0000 |
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> From: Lu Baolu <baolu.lu@linux.intel.com> > Sent: Friday, April 22, 2022 9:04 PM > > On 2022/4/22 10:47, Tian, Kevin wrote: > >> From: Lu Baolu > >> Sent: Thursday, April 21, 2022 7:36 PM > >> > >> The latest VT-d specification states that the PGSNP field in the pasid > >> table entry should be treated as Reserved(0) for implementations not > >> supporting Snoop Control (SC=0 in the Extended Capability Register). > >> This adds a check before setting the field. > >> > >> Signed-off-by: Lu Baolu<baolu.lu@linux.intel.com> > >> --- > >> drivers/iommu/intel/pasid.c | 13 ++++++++++--- > >> 1 file changed, 10 insertions(+), 3 deletions(-) > >> > >> diff --git a/drivers/iommu/intel/pasid.c b/drivers/iommu/intel/pasid.c > >> index f8d215d85695..5cb2daa2b8cb 100644 > >> --- a/drivers/iommu/intel/pasid.c > >> +++ b/drivers/iommu/intel/pasid.c > >> @@ -625,8 +625,14 @@ int intel_pasid_setup_first_level(struct > intel_iommu > >> *iommu, > >> } > >> } > >> > >> - if (flags & PASID_FLAG_PAGE_SNOOP) > >> - pasid_set_pgsnp(pte); > >> + if (flags & PASID_FLAG_PAGE_SNOOP) { > >> + if (ecap_sc_support(iommu->ecap)) { > >> + pasid_set_pgsnp(pte); > >> + } else { > >> + pasid_clear_entry(pte); > >> + return -EINVAL; > >> + } > >> + } > >> > >> pasid_set_domain_id(pte, did); > >> pasid_set_address_width(pte, iommu->agaw); > >> @@ -710,7 +716,8 @@ int intel_pasid_setup_second_level(struct > >> intel_iommu *iommu, > >> pasid_set_fault_enable(pte); > >> pasid_set_page_snoop(pte, !!ecap_smpwc(iommu->ecap)); > >> > >> - if (domain->domain.type == IOMMU_DOMAIN_UNMANAGED) > >> + if (ecap_sc_support(iommu->ecap) && > >> + domain->domain.type == IOMMU_DOMAIN_UNMANAGED) > >> pasid_set_pgsnp(pte); > >> > > This should be rebased on top of Jason's enforce coherency series > > instead of blindly setting it. No matter whether it's legacy mode > > where we set SNP in PTE or scalable mode where we set PGSNP > > in PASID entry for entire page table, the trigger point should be > > same i.e. when someone calls enforce_cache_coherency(). > > With Jason's enforce coherency series merged, we even don't need to set > PGSNP bit of a pasid entry for second level translation. 2nd level > always supports SNP in PTEs, so set PGSNP in pasid table entry is > unnecessary. >
Yes, this sounds correct for 2nd-level.
but setting PGSNP of 1st level translation is also relevant to that change when talking about enforcing coherency in the guest. In this case PASID_FLAG_PAGE_SNOOP should be set also after enforce_cache_coherency() is called.
Currently it's always set for unmanaged domain in domain_setup_first_level():
if (domain->domain.type == IOMMU_DOMAIN_UNMANAGED) flags |= PASID_FLAG_PAGE_SNOOP;
Suppose we need a separate interface to update PGSNP after pasid entry is set up.
Thanks Kevin
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