linux-kernel - [PATCH] x86/sev: Don't hang but terminate on failure to remap SVSM CA

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Message-ID: <20250106155745.281221-2-ardb+git@google.com>
Date: Mon,  6 Jan 2025 16:57:46 +0100
From: Ard Biesheuvel <ardb+git@...gle.com>
To: linux-kernel@...r.kernel.org
Cc: x86@...nel.org, Ard Biesheuvel <ardb@...nel.org>, Tom Lendacky <thomas.lendacky@....com>
Subject: [PATCH] x86/sev: Don't hang but terminate on failure to remap SVSM CA

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

Commit

  09d35045cd0f  ("x86/sev: Avoid WARN()s and panic()s in early boot code")

replaced a panic() that could potentially hit before the kernel is even
mapped with a deadloop, to ensure that execution does not proceed when
the condition in question hits.

As Tom suggests, it is better to terminate and return to the hypervisor
in this case, using a newly invented failure code to describe the
failure condition.

Suggested-by: Tom Lendacky <thomas.lendacky@....com>
Link: https://lore.kernel.org/all/9ce88603-20ca-e644-2d8a-aeeaf79cde69@amd.com
Signed-off-by: Ard Biesheuvel <ardb@...nel.org>
---
 arch/x86/coco/sev/core.c          | 4 ++--
 arch/x86/include/asm/sev-common.h | 1 +
 2 files changed, 3 insertions(+), 2 deletions(-)

diff --git a/arch/x86/coco/sev/core.c b/arch/x86/coco/sev/core.c
index 499b41953e3c..86898547056e 100644
--- a/arch/x86/coco/sev/core.c
+++ b/arch/x86/coco/sev/core.c
@@ -2356,8 +2356,8 @@ static __head void svsm_setup(struct cc_blob_sev_info *cc_info)
 	call.rax = SVSM_CORE_CALL(SVSM_CORE_REMAP_CA);
 	call.rcx = pa;
 	ret = svsm_perform_call_protocol(&call);
-	while (ret)
-		cpu_relax(); /* too early to panic */
+	if (ret)
+		sev_es_terminate(SEV_TERM_SET_LINUX, GHCB_TERM_SVSM_CA_REMAP_FAIL);
 
 	RIP_REL_REF(boot_svsm_caa) = (struct svsm_ca *)pa;
 	RIP_REL_REF(boot_svsm_caa_pa) = pa;
diff --git a/arch/x86/include/asm/sev-common.h b/arch/x86/include/asm/sev-common.h
index 50f5666938c0..577b64dda8b4 100644
--- a/arch/x86/include/asm/sev-common.h
+++ b/arch/x86/include/asm/sev-common.h
@@ -206,6 +206,7 @@ struct snp_psc_desc {
 #define GHCB_TERM_NO_SVSM		7	/* SVSM is not advertised in the secrets page */
 #define GHCB_TERM_SVSM_VMPL0		8	/* SVSM is present but has set VMPL to 0 */
 #define GHCB_TERM_SVSM_CAA		9	/* SVSM is present but CAA is not page aligned */
+#define GHCB_TERM_SVSM_CA_REMAP_FAIL	10	/* SVSM is present but CA could not be remapped */
 
 #define GHCB_RESP_CODE(v)		((v) & GHCB_MSR_INFO_MASK)
 
-- 
2.47.1.613.gc27f4b7a9f-goog