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    SubjectRe: [PATCH Part2 v6 07/49] x86/sev: Invalid pages from direct map when adding it to RMP table
    On Mon, Jun 20, 2022 at 4:03 PM Ashish Kalra <Ashish.Kalra@amd.com> 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 checks failure, it raises a page-fault exception.

    nit: "RMP checks ..." -> "RMP-check ..."

    >
    > 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
    > invalid state so that pages cannot be used in the direct-map after its

    nit: "invalid state ..." -> "invalidate state ..."
    nit: "... after its" -> "... after they're"

    (Here, and in the patch subject too.)

    > added in the RMP table, and restore to its default valid permission after

    nit: "... restore to its ..." -> "... restored to their ..."

    > the pages are removed from the RMP table.
    >
    > Signed-off-by: Brijesh Singh <brijesh.singh@amd.com>
    > ---
    > arch/x86/kernel/sev.c | 61 ++++++++++++++++++++++++++++++++++++++++++-
    > 1 file changed, 60 insertions(+), 1 deletion(-)
    >
    > diff --git a/arch/x86/kernel/sev.c b/arch/x86/kernel/sev.c
    > index f6c64a722e94..734cddd837f5 100644
    > --- a/arch/x86/kernel/sev.c
    > +++ b/arch/x86/kernel/sev.c
    > @@ -2451,10 +2451,42 @@ int psmash(u64 pfn)
    > }
    > EXPORT_SYMBOL_GPL(psmash);
    >
    > +static int restore_direct_map(u64 pfn, int npages)
    > +{
    > + int i, ret = 0;
    > +
    > + for (i = 0; i < npages; i++) {
    > + ret = set_direct_map_default_noflush(pfn_to_page(pfn + i));
    > + if (ret)
    > + goto cleanup;
    > + }
    > +
    > +cleanup:
    > + WARN(ret > 0, "Failed to restore direct map for pfn 0x%llx\n", pfn + i);
    > + return ret;
    > +}
    > +
    > +static int invalid_direct_map(unsigned long pfn, int npages)

    I think we should rename this function to "invalidate_direct_map()".

    > +{
    > + int i, ret = 0;
    > +
    > + for (i = 0; i < npages; i++) {
    > + ret = set_direct_map_invalid_noflush(pfn_to_page(pfn + i));
    > + if (ret)
    > + goto cleanup;
    > + }
    > +
    > + return 0;
    > +
    > +cleanup:
    > + restore_direct_map(pfn, i);
    > + return ret;
    > +}
    > +
    > static int rmpupdate(u64 pfn, struct rmpupdate *val)
    > {
    > unsigned long paddr = pfn << PAGE_SHIFT;
    > - int ret;
    > + int ret, level, npages;
    >
    > if (!pfn_valid(pfn))
    > return -EINVAL;
    > @@ -2462,11 +2494,38 @@ static int rmpupdate(u64 pfn, struct rmpupdate *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.
    > + */
    > + if (val->assigned) {
    > + if (invalid_direct_map(pfn, npages)) {
    > + pr_err("Failed to unmap pfn 0x%llx pages %d from direct_map\n",
    > + pfn, npages);
    > + return -EFAULT;
    > + }
    > + }
    > +
    > /* Binutils version 2.36 supports the RMPUPDATE mnemonic. */
    > asm volatile(".byte 0xF2, 0x0F, 0x01, 0xFE"
    > : "=a"(ret)
    > : "a"(paddr), "c"((unsigned long)val)
    > : "memory", "cc");
    > +
    > + /*
    > + * Restore the direct map after the page is removed from the RMP table.
    > + */
    > + if (!ret && !val->assigned) {
    > + if (restore_direct_map(pfn, npages)) {
    > + pr_err("Failed to map pfn 0x%llx pages %d in direct_map\n",
    > + pfn, npages);
    > + return -EFAULT;
    > + }
    > + }
    > +
    > return ret;
    > }
    >
    > --
    > 2.25.1
    >
    >

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