linux-kernel - [PATCH v6 04/22] x86/sev: Run RMPADJUST on SVSM calling area page to test VMPL

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Message-ID: <20250722072708.2079165-28-ardb+git@google.com>
Date: Tue, 22 Jul 2025 09:27:13 +0200
From: Ard Biesheuvel <ardb+git@...gle.com>
To: linux-kernel@...r.kernel.org
Cc: linux-efi@...r.kernel.org, x86@...nel.org, 
	Ard Biesheuvel <ardb@...nel.org>, Borislav Petkov <bp@...en8.de>, Ingo Molnar <mingo@...nel.org>, 
	Kevin Loughlin <kevinloughlin@...gle.com>, Tom Lendacky <thomas.lendacky@....com>, 
	Josh Poimboeuf <jpoimboe@...nel.org>, Peter Zijlstra <peterz@...radead.org>, 
	Nikunj A Dadhania <nikunj@....com>
Subject: [PATCH v6 04/22] x86/sev: Run RMPADJUST on SVSM calling area page to
 test VMPL

From: Ard Biesheuvel <ardb@...nel.org>

Determining the VMPL at which the kernel runs involves performing a
RMPADJUST operation on an arbitrary page of memory, and observing whether
it succeeds.

The use of boot_ghcb_page in the core kernel in this case is completely
arbitrary, but results in the need to provide a PIC alias for it. So use
boot_svsm_ca_page instead, which already needs this alias for other
reasons.

Signed-off-by: Ard Biesheuvel <ardb@...nel.org>
Reviewed-by: Tom Lendacky <thomas.lendacky@....com>
---
 arch/x86/boot/compressed/sev.c      | 2 +-
 arch/x86/boot/startup/sev-shared.c  | 5 +++--
 arch/x86/boot/startup/sev-startup.c | 2 +-
 3 files changed, 5 insertions(+), 4 deletions(-)

diff --git a/arch/x86/boot/compressed/sev.c b/arch/x86/boot/compressed/sev.c
index b71c1ab6a282..3628e9bddc6a 100644
--- a/arch/x86/boot/compressed/sev.c
+++ b/arch/x86/boot/compressed/sev.c
@@ -327,7 +327,7 @@ static bool early_snp_init(struct boot_params *bp)
 	 * running at VMPL0. The CA will be used to communicate with the
 	 * SVSM and request its services.
 	 */
-	svsm_setup_ca(cc_info);
+	svsm_setup_ca(cc_info, rip_rel_ptr(&boot_ghcb_page));
 
 	/*
 	 * Pass run-time kernel a pointer to CC info via boot_params so EFI
diff --git a/arch/x86/boot/startup/sev-shared.c b/arch/x86/boot/startup/sev-shared.c
index 9a5fd194101b..7ac5c50722b4 100644
--- a/arch/x86/boot/startup/sev-shared.c
+++ b/arch/x86/boot/startup/sev-shared.c
@@ -793,7 +793,8 @@ static void __head pvalidate_4k_page(unsigned long vaddr, unsigned long paddr,
  * Maintain the GPA of the SVSM Calling Area (CA) in order to utilize the SVSM
  * services needed when not running in VMPL0.
  */
-static bool __head svsm_setup_ca(const struct cc_blob_sev_info *cc_info)
+static bool __head svsm_setup_ca(const struct cc_blob_sev_info *cc_info,
+				 void *page)
 {
 	struct snp_secrets_page *secrets_page;
 	struct snp_cpuid_table *cpuid_table;
@@ -816,7 +817,7 @@ static bool __head svsm_setup_ca(const struct cc_blob_sev_info *cc_info)
 	 * routine is running identity mapped when called, both by the decompressor
 	 * code and the early kernel code.
 	 */
-	if (!rmpadjust((unsigned long)rip_rel_ptr(&boot_ghcb_page), RMP_PG_SIZE_4K, 1))
+	if (!rmpadjust((unsigned long)page, RMP_PG_SIZE_4K, 1))
 		return false;
 
 	/*
diff --git a/arch/x86/boot/startup/sev-startup.c b/arch/x86/boot/startup/sev-startup.c
index 8412807a865c..3da04a715831 100644
--- a/arch/x86/boot/startup/sev-startup.c
+++ b/arch/x86/boot/startup/sev-startup.c
@@ -302,7 +302,7 @@ static __head void svsm_setup(struct cc_blob_sev_info *cc_info)
 	 * running at VMPL0. The CA will be used to communicate with the
 	 * SVSM to perform the SVSM services.
 	 */
-	if (!svsm_setup_ca(cc_info))
+	if (!svsm_setup_ca(cc_info, rip_rel_ptr(&boot_svsm_ca_page)))
 		return;
 
 	/*
-- 
2.50.0.727.gbf7dc18ff4-goog