Messages in this thread |  | | Date | Sun, 24 Apr 2022 14:23:38 +0800 | Subject | Re: [PATCH v2 1/4] iommu/vt-d: Check before setting PGSNP bit in pasid table entry | From | Lu Baolu <> |
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On 2022/4/24 13:55, Tian, Kevin wrote: >> From: Lu Baolu <baolu.lu@linux.intel.com> >> Sent: Sunday, April 24, 2022 12:38 PM >> >> On 2022/4/24 11:37, Tian, Kevin wrote: >>>>> 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. >> >> Yes. Agreed. >> >>> 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. >> >> Currently enforcing coherency is only used in VFIO. In the VFIO use >> case, it's safe to always set PGSNP when an UNMANAGED domain is attached >> on the first level pasid translation. We could add support of updating >> PGSNP after pasid entry setup once there's a real need. >> > > The real need is here. The iommu driver should not assume the > policy of VFIO, which is already communicated via the new > enforce_cache_coherency() interface. The same policy should > apply no matter whether 1st or 2nd level is in-use.
Okay, I think I will move this patch out of this series and put it in a separated one for VT-d improvements after Jason's enforcing snoop series gets merged. Thanks for your suggestions.
Best regards, baolu
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