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

    Just typos:

    On Mon, Oct 16, 2023 at 08:27:52AM -0500, Michael Roth wrote:
    > From: Brijesh Singh <brijesh.singh@amd.com>
    >
    > 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

    "hugepage"

    > incorrectly treat the entire 2mb region as in-use and signal a spurious
    > RMP violation #PF.
    >
    > The recommended is to not use the hugepage for the VMCB, VMSA or

    s/recommended/recommendation/
    s/the hugepage/a hugepage/

    > AVIC backing page for similar reasons. Add a generic allocator that will
    > ensure that the page returns is not hugepage (2mb or 1gb) and is safe to

    "... the page returned is not a hugepage..."

    ...

    > +struct page *snp_safe_alloc_page(struct kvm_vcpu *vcpu)
    > +{
    > + unsigned long pfn;
    > + struct page *p;
    > +
    > + if (!cpu_feature_enabled(X86_FEATURE_SEV_SNP))
    > + return alloc_page(GFP_KERNEL_ACCOUNT | __GFP_ZERO);
    > +
    > + /*
    > + * Allocate an SNP safe page to workaround the SNP erratum where
    > + * the CPU will incorrectly signal an RMP violation #PF if a
    > + * hugepage (2mb or 1gb) collides with the RMP entry of VMCB, VMSA
    > + * or AVIC backing page. The recommeded workaround is to not use the

    "recommended"

    > + * hugepage.
    > + *
    > + * Allocate one extra page, use a page which is not 2mb aligned
    > + * and free the other.
    > + */
    > + p = alloc_pages(GFP_KERNEL_ACCOUNT | __GFP_ZERO, 1);
    > + if (!p)
    > + return NULL;
    > +
    > + split_page(p, 1);
    > +
    > + pfn = page_to_pfn(p);
    > + if (IS_ALIGNED(pfn, PTRS_PER_PMD))
    > + __free_page(p++);
    > + else
    > + __free_page(p + 1);
    > +
    > + return p;
    > +}

    --
    Regards/Gruss,
    Boris.

    https://people.kernel.org/tglx/notes-about-netiquette

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