[PATCH v7 04/22] x86/sev: Run RMPADJUST on SVSM calling area page to test VMPL

Ard Biesheuvel
2025-08-28T10:22:40Z

From: Ard Biesheuvel <ardb@kernel.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@kernel.org>
Reviewed-by: Tom Lendacky <thomas.lendacky@amd.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 7bd73462c11e..83c222a4f1fa 100644
--- a/arch/x86/boot/startup/sev-shared.c
+++ b/arch/x86/boot/startup/sev-shared.c
@@ -801,7 +801,8 @@ 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;
@@ -824,7 +825,7 @@ 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;

/*
--
2.51.0.268.g9569e192d0-goog