[tip: x86/sev] x86/boot: Drop redundant RMPADJUST in SEV SVSM presence check

["tip-bot2 for Ard Biesheuvel" <tip-bot2@linutronix.de>]

The following commit has been merged into the x86/sev branch of tip:

Commit-ID:     68a501d7fd82454525797971c6a0005ceeb93153
Gitweb:        https://git.kernel.org/tip/68a501d7fd82454525797971c6a0005ceeb93153
Author:        Ard Biesheuvel <ardb@kernel.org>
AuthorDate:    Thu, 28 Aug 2025 12:22:13 +02:00
Committer:     Borislav Petkov (AMD) <bp@alien8.de>
CommitterDate: Wed, 03 Sep 2025 17:59:09 +02:00

x86/boot: Drop redundant RMPADJUST in SEV SVSM presence check

snp_vmpl will be assigned a non-zero value when executing at a VMPL other than
0, and this is inferred from a call to RMPADJUST, which only works when
running at VMPL0.

This means that testing snp_vmpl is sufficient, and there is no need to
perform the same check again.

Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Link: https://lore.kernel.org/20250828102202.1849035-34-ardb+git@google.com
---
 arch/x86/boot/compressed/sev.c | 20 +++-----------------
 1 file changed, 3 insertions(+), 17 deletions(-)

diff --git a/arch/x86/boot/compressed/sev.c b/arch/x86/boot/compressed/sev.c
index 4873469..26aa389 100644
--- a/arch/x86/boot/compressed/sev.c
+++ b/arch/x86/boot/compressed/sev.c
@@ -406,30 +406,16 @@ void sev_enable(struct boot_params *bp)
 	 */
 	if (sev_status & MSR_AMD64_SEV_SNP_ENABLED) {
 		u64 hv_features;
-		int ret;
 
 		hv_features = get_hv_features();
 		if (!(hv_features & GHCB_HV_FT_SNP))
 			sev_es_terminate(SEV_TERM_SET_GEN, GHCB_SNP_UNSUPPORTED);
 
 		/*
-		 * Enforce running at VMPL0 or with an SVSM.
-		 *
-		 * Use RMPADJUST (see the rmpadjust() function for a description of
-		 * what the instruction does) to update the VMPL1 permissions of a
-		 * page. If the guest is running at VMPL0, this will succeed. If the
-		 * guest is running at any other VMPL, this will fail. Linux SNP guests
-		 * only ever run at a single VMPL level so permission mask changes of a
-		 * lesser-privileged VMPL are a don't-care.
+		 * Running at VMPL0 is required unless an SVSM is present and
+		 * the hypervisor supports the required SVSM GHCB events.
 		 */
-		ret = rmpadjust((unsigned long)&boot_ghcb_page, RMP_PG_SIZE_4K, 1);
-
-		/*
-		 * Running at VMPL0 is not required if an SVSM is present and the hypervisor
-		 * supports the required SVSM GHCB events.
-		 */
-		if (ret &&
-		    !(snp_vmpl && (hv_features & GHCB_HV_FT_SNP_MULTI_VMPL)))
+		if (snp_vmpl && !(hv_features & GHCB_HV_FT_SNP_MULTI_VMPL))
 			sev_es_terminate(SEV_TERM_SET_LINUX, GHCB_TERM_NOT_VMPL0);
 	}