On Wed, Feb 05, 2025, Ashish Kalra wrote: > On 2/5/2025 1:31 PM, Sean Christopherson wrote: > > On Wed, Feb 05, 2025, Vasant Hegde wrote: > >> So we don't want to clear CC_ATTR_HOST_SEV_SNP after RMP initialization -OR- > >> clear for all failures? > > > > I honestly don't know, because the answer largely depends on what happens with > > hardware. I asked in an earlier version of this series if IOMMU initialization > > failure after the RMP is configured is even survivable. > > > > As i mentioned earlier and as part of this series and summarizing this again here: Thanks! > - snp_rmptable_init() enables SNP support system-wide and that means the HW starts > doing RMP checks for memory accesses, but as RMP table is zeroed out initially, > all memory is configured to be host/HV owned. > > It is only after SNP_INIT(_EX) that RMP table is configured and initialized with > HV_Fixed, firmware pages and stuff like IOMMU RMP enforcement is enabled. > > If the IOMMU initialization fails after IOMMU support on SNP check is completed > and host SNP is enabled, then SNP_INIT(_EX) will fail as IOMMUs need to be enabled > for SNP_INIT to succeed. > > > For this series, I think it makes sense to match the existing behavior, unless > > someone from AMD can definitively state that we should do something different. > > And the existing behavior is that amd_iommu_snp_en and CC_ATTR_HOST_SEV_SNP will > > be left set if the IOMMU completes iommu_snp_enable(), and the kernel completes > > RMP setup. > > Yes, that is true and this behavior is still consistent with this series. > > Again to reiterate, if iommu_snp_enable() and host SNP enablement is successful, > any late IOMMU initialization failures should cause SNP_INIT to fail and that means > IOMMU RMP enforcement will never get enabled and RMP table will remain configured > for all memory marked as HV/host owned. So the kernel should be able to limp along, but CC_ATTR_HOST_SEV_SNP will be in a half-baked state. Would it make sense to WARN if the RMP has been configured? E.g. as a follow-up change: /* * SNP platform initilazation requires IOMMUs to be fully configured. * If the RMP has NOT been configured, simply mark SNP as unsupported. * If the RMP is configured, but RMP enforcement has not been enabled * in IOMMUs, then the system is in a half-baked state, but can limp * along as all memory should be Hypervisor-Owned in the RMP. WARN, * but leave SNP as "supported" to avoid confusing the kernel. */ if (ret && cc_platform_has(CC_ATTR_HOST_SEV_SNP) && !WARN_ON_ONCE(amd_iommu_snp_en)) cc_platform_clear(CC_ATTR_HOST_SEV_SNP);
