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    SubjectRe: [PATCH RFC v8 15/56] x86/sev: Invalidate pages from the direct map when adding them to the RMP table
    On Mon, Feb 20, 2023 at 12:38:06PM -0600, 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.
    >
    > Co-developed-by: Ashish Kalra <ashish.kalra@amd.com>
    > Signed-off-by: Ashish Kalra <ashish.kalra@amd.com>
    > Signed-off-by: Brijesh Singh <brijesh.singh@amd.com>
    > Signed-off-by: Michael Roth <michael.roth@amd.com>
    > ---
    > arch/x86/kernel/sev.c | 57 +++++++++++++++++++++++++++++++++++++++++++
    > 1 file changed, 57 insertions(+)
    >
    > diff --git a/arch/x86/kernel/sev.c b/arch/x86/kernel/sev.c
    > index a49f30c10dc1..3e5ff5934e83 100644
    > --- a/arch/x86/kernel/sev.c
    > +++ b/arch/x86/kernel/sev.c
    > @@ -2595,6 +2595,37 @@ 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 invalidate_direct_map(u64 pfn, int npages)
    > +{
    > + 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;
    > + }
    > +
    > +cleanup:
    > + WARN(ret > 0, "Failed to invalidate direct map for pfn 0x%llx\n", pfn + i);
    > + restore_direct_map(pfn, i);

    This immediately restores the direct map after invalidating it. It
    probably needs to put behind if(ret).

    Regards, Tom

    > + return ret;
    > +}
    > +
    > static int rmpupdate(u64 pfn, struct rmp_state *val)
    > {
    > int max_attempts = 4 * num_present_cpus();
    > @@ -2605,6 +2636,21 @@ 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.
    > + */
    > + 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);
    > + return -EFAULT;
    > + }
    > + }
    > +
    > do {
    > /* Binutils version 2.36 supports the RMPUPDATE mnemonic. */
    > asm volatile(".byte 0xF2, 0x0F, 0x01, 0xFE"
    > @@ -2630,6 +2676,17 @@ static int rmpupdate(u64 pfn, struct rmp_state *val)
    > attempts, val->asid, ret, pfn, npages);
    > }
    >
    > + /*
    > + * 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);
    > + return -EFAULT;
    > + }
    > + }
    > +
    > return 0;
    > }
    >
    > --
    > 2.25.1
    >

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