linux-kernel - [PATCH v5 02/22] x86/sev: Use MSR protocol for remapping SVSM calling area

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Message-ID: <20250716031814.2096113-26-ardb+git@google.com>
Date: Wed, 16 Jul 2025 05:18:17 +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 v5 02/22] x86/sev: Use MSR protocol for remapping SVSM calling area

From: Ard Biesheuvel <ardb@...nel.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@...nel.org>
Reviewed-by: Borislav Petkov (AMD) <bp@...en8.de>
Reviewed-by: Tom Lendacky <thomas.lendacky@....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 c401d0391537..60ab09b3149d 100644
--- a/arch/x86/boot/startup/sev-shared.c
+++ b/arch/x86/boot/startup/sev-shared.c
@@ -723,6 +723,17 @@ 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..c30e0eed0131 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_perform_msr_protocol(&call))
 		sev_es_terminate(SEV_TERM_SET_LINUX, GHCB_TERM_SVSM_CA_REMAP_FAIL);
 
 	boot_svsm_caa = (struct svsm_ca *)pa;
-- 
2.50.0.727.gbf7dc18ff4-goog