Re: [PATCH v10 23/50] KVM: SEV: Make AVIC backing, VMSA and VMCB memory allocation SNP safe

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On 10/16/23 15:27, Michael Roth wrote:
From: Brijesh Singh <brijesh.singh@xxxxxxx>

Implement a workaround for an SNP erratum where the CPU will incorrectly
signal an RMP violation #PF if a hugepage (2mb or 1gb) collides with the
RMP entry of a VMCB, VMSA or AVIC backing page.

When SEV-SNP is globally enabled, the CPU marks the VMCB, VMSA, and AVIC
backing pages as "in-use" via a reserved bit in the corresponding RMP
entry after a successful VMRUN. This is done for _all_ VMs, not just
SNP-Active VMs.

If the hypervisor accesses an in-use page through a writable
translation, the CPU will throw an RMP violation #PF. On early SNP
hardware, if an in-use page is 2mb aligned and software accesses any
part of the associated 2mb region with a hupage, the CPU will
incorrectly treat the entire 2mb region as in-use and signal a spurious
RMP violation #PF.

I don't understand if this can happen even if SEV-SNP is not in use, just because it is supported on the host? If so, should this be Cc'd to stable? (I can tweak the wording and submit it).

Paolo





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