[PATCH v7 02/22] x86/sev: Use MSR protocol for remapping SVSM calling area

Ard Biesheuvel
2025-08-28T10:22:38Z

From: Ard Biesheuvel <ardb@kernel.org>

As the preceding code comment already indicates, remapping the SVSM
calling area occurs long before the GHCB page is configured, and so
calling svsm_perform_call_protocol() is guaranteed to result in a call
to svsm_perform_msr_protocol().

So just call the latter directly. This allows most of the GHCB based API
infrastructure to be moved out of the startup code in a subsequent
patch.

Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Reviewed-by: Borislav Petkov (AMD) <bp@alien8.de>
Reviewed-by: Tom Lendacky <thomas.lendacky@amd.com>
---
arch/x86/boot/startup/sev-shared.c | 11 +++++++++++
arch/x86/boot/startup/sev-startup.c | 5 ++---
2 files changed, 13 insertions(+), 3 deletions(-)

diff --git a/arch/x86/boot/startup/sev-shared.c b/arch/x86/boot/startup/sev-shared.c
index ed88dfe7605e..975d2b02926a 100644
--- a/arch/x86/boot/startup/sev-shared.c
+++ b/arch/x86/boot/startup/sev-shared.c
@@ -724,6 +724,17 @@ static void __head setup_cpuid_table(const struct cc_blob_sev_info *cc_info)
}
}

+static int __head svsm_call_msr_protocol(struct svsm_call *call)
+{
+ int ret;
+
+ do {
+ ret = svsm_perform_msr_protocol(call);
+ } while (ret == -EAGAIN);
+
+ return ret;
+}
+
static void __head svsm_pval_4k_page(unsigned long paddr, bool validate)
{
struct svsm_pvalidate_call *pc;
diff --git a/arch/x86/boot/startup/sev-startup.c b/arch/x86/boot/startup/sev-startup.c
index 0b7e3b950183..8412807a865c 100644
--- a/arch/x86/boot/startup/sev-startup.c
+++ b/arch/x86/boot/startup/sev-startup.c
@@ -295,7 +295,6 @@ static __head struct cc_blob_sev_info *find_cc_blob(struct boot_params *bp)
static __head void svsm_setup(struct cc_blob_sev_info *cc_info)
{
struct svsm_call call = {};
- int ret;
u64 pa;

/*
@@ -325,8 +324,8 @@ static __head void svsm_setup(struct cc_blob_sev_info *cc_info)
call.caa = svsm_get_caa();
call.rax = SVSM_CORE_CALL(SVSM_CORE_REMAP_CA);
call.rcx = pa;
- ret = svsm_perform_call_protocol(&call);
- if (ret)
+
+ if (svsm_call_msr_protocol(&call))
sev_es_terminate(SEV_TERM_SET_LINUX, GHCB_TERM_SVSM_CA_REMAP_FAIL);

boot_svsm_caa = (struct svsm_ca *)pa;
--
2.51.0.268.g9569e192d0-goog