Hi Sean, On 10/30/2024 12:57 PM, Sean Christopherson wrote: > On Wed, Oct 30, 2024, Pratik R. Sampat wrote: >> On 10/30/2024 8:46 AM, Sean Christopherson wrote: >>> +/* Minimum firmware version required for the SEV-SNP support */ >>> +#define SNP_FW_REQ_VER_MAJOR 1 >>> +#define SNP_FW_REQ_VER_MINOR 51 >>> >>> Side topic, why are these hardcoded? And where did they come from? If >>> they're >>> arbitrary KVM selftests values, make that super duper clear. >> >> Well, it's not entirely arbitrary. This was the version that SNP GA'd >> with first so that kind of became the minimum required version needed. >> >> I think the only place we've documented this is here - >> https://github.com/AMDESE/AMDSEV/tree/snp-latest?tab=readme-ov-file#upgrade-sev-firmware. >> >> Maybe, I can modify the comment above to say something like - >> Minimum general availability release firmware required for SEV-SNP support. > > Hmm, so if AMD says SNP is only supported for firmware version >= 1.51, why on > earth is that not checked and enforced by the kernel? Relying on userspace to > not crash the host (or worse) because of unsupported firmware is not a winning > strategy.
We do check against the firmware level 1.51 while setting things up first (drivers/crypto/ccp/sev-dev.c:__sev_snp_init_locked()) and we bail out if it's otherwise. From the userspace, calls to KVM_SEV_INIT2 or any other corresponding SNP calls should fail cleanly without any adverse effects to the host. >From the positive selftest perspective though, we want to make sure it's both supported and enabled, and skip the test if not. I believe we can tell if it's supported by the platform using the MSR - MSR_AMD64_SEV_SNP_ENABLED or the X86_FEATURE_SEV_SNP from the KVM capabilities. However, to determine if it's enabled from the kernel, I made this check here. Having said that, I do agree that there should probably be a better way to expose this support to the userspace. Thanks Pratik
