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    SubjectRe: [PATCH v10 12/50] x86/sev: Invalidate pages from the direct map when adding them to the RMP table
    On Mon, Oct 16, 2023 at 08:27:41AM -0500, Michael Roth wrote:
    > From: Brijesh Singh <brijesh.singh@amd.com>
    >
    > The integrity guarantee of SEV-SNP is enforced through the RMP table.
    > The RMP is used with standard x86 and IOMMU page tables to enforce
    > memory restrictions and page access rights. The RMP check is enforced as
    > soon as SEV-SNP is enabled globally in the system. When hardware
    > encounters an RMP-check failure, it raises a page-fault exception.
    >
    > The rmp_make_private() and rmp_make_shared() helpers are used to add
    > or remove the pages from the RMP table. Improve the rmp_make_private()
    > to invalidate state so that pages cannot be used in the direct-map after
    > they are added the RMP table, and restored to their default valid
    > permission after the pages are removed from the RMP table.

    Brijesh's SOB comes

    <--- here,

    then Ashish's two tags.

    Please audit your whole set for such inconsistencies.

    > @@ -404,6 +440,21 @@ static int rmpupdate(u64 pfn, struct rmp_state *val)
    > if (!cpu_feature_enabled(X86_FEATURE_SEV_SNP))
    > return -ENXIO;
    >
    > + level = RMP_TO_X86_PG_LEVEL(val->pagesize);
    > + npages = page_level_size(level) / PAGE_SIZE;
    > +
    > + /*
    > + * If page is getting assigned in the RMP table then unmap it from the
    > + * direct map.

    Here I'm missing the explanation *why* the pages need to be unmapped
    from the direct map.

    What happens if not?

    > + */
    > + if (val->assigned) {
    > + if (invalidate_direct_map(pfn, npages)) {
    > + pr_err("Failed to unmap %d pages at pfn 0x%llx from the direct_map\n",
    > + npages, pfn);

    invalidate_direct_map() already dumps an error message - no need to do
    that here too.

    > + return -EFAULT;
    > + }
    > + }
    > +
    > do {
    > /* Binutils version 2.36 supports the RMPUPDATE mnemonic. */
    > asm volatile(".byte 0xF2, 0x0F, 0x01, 0xFE"
    > @@ -422,6 +473,17 @@ static int rmpupdate(u64 pfn, struct rmp_state *val)
    > return -EFAULT;
    > }
    >
    > + /*
    > + * Restore the direct map after the page is removed from the RMP table.
    > + */
    > + if (!val->assigned) {
    > + if (restore_direct_map(pfn, npages)) {
    > + pr_err("Failed to map %d pages at pfn 0x%llx into the direct_map\n",
    > + npages, pfn);

    Ditto.

    --
    Regards/Gruss,
    Boris.

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

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