Re: [PATCH Part2 v6 07/49] x86/sev: Invalid pages from direct map when adding it to RMP table

Borislav Petkov
2022-07-27T17:01:54Z

On Mon, Jun 20, 2022 at 11:03:07PM +0000, Ashish Kalra wrote:

> Subject: x86/sev: Invalid pages from direct map when adding it to RMP table

"...: Invalidate pages from the direct map when adding them to the RMP table"

> +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));

set_memory_p() ?

> + if (ret)
> + goto cleanup;
> + }
> +
> +cleanup:
> + WARN(ret > 0, "Failed to restore direct map for pfn 0x%llx\n", pfn + i);

Warn for each pfn?!

That'll flood dmesg mightily.

> + return ret;
> +}
> +
> +static int invalid_direct_map(unsigned long pfn, int npages)
> +{
> + int i, ret = 0;
> +
> + for (i = 0; i < npages; i++) {
> + ret = set_direct_map_invalid_noflush(pfn_to_page(pfn + i));

As above, set_memory_np() doesn't work here instead of looping over each
page?

> @@ -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",

"Failed to unmap %d pages at pfn 0x... from the 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",

"Failed to map %d pages at pfn 0x... into the direct map\n"

Thx.

--
Regards/Gruss,
Boris.