On 2/5/2025 1:31 PM, Sean Christopherson wrote: > On Wed, Feb 05, 2025, Vasant Hegde wrote: >> On 2/5/2025 8:47 PM, Sean Christopherson wrote: >>> On Wed, Feb 05, 2025, Vasant Hegde wrote: >>>>> @@ -3318,6 +3326,9 @@ static int __init iommu_go_to_state(enum iommu_init_state state) >>>>> ret = state_next(); >>>>> } >>>>> >>>>> + if (ret && !amd_iommu_snp_en && cc_platform_has(CC_ATTR_HOST_SEV_SNP)) >>>> >>>> >>>> I think we should clear when `amd_iommu_snp_en` is true. >>> >>> That doesn't address the case where amd_iommu_prepare() fails, because amd_iommu_snp_en >>> will be %false (its init value) and the RMP will be uninitialized, i.e. >>> CC_ATTR_HOST_SEV_SNP will be incorrectly left set. >> >> You are right. I missed early failure scenarios :-( >> >>> >>> And conversely, IMO clearing CC_ATTR_HOST_SEV_SNP after initializing the IOMMU >>> and RMP is wrong as well. Such a host is probably hosed regardless, but from >>> the CPU's perspective, SNP is supported and enabled. >> >> 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: - 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. Thanks, Ashish
