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From:   Marc Orr <marcorr@google.com>
Date:   Thu, 23 Jun 2022 17:06:16 -0700
Message-ID: <CAA03e5HDxkhV1rnVfPj7W_Hf85JMAG0s8eLKN6hA0n4sCy8tww@mail.gmail.com>
Subject: Re: [PATCH Part2 v6 07/49] x86/sev: Invalid pages from direct map
 when adding it to RMP table
To:     Ashish Kalra <Ashish.Kalra@amd.com>
Cc:     x86 <x86@kernel.org>, LKML <linux-kernel@vger.kernel.org>,
        kvm list <kvm@vger.kernel.org>, linux-coco@lists.linux.dev,
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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
>
>