linux-kernel - [PATCH v5 10/10] x86/sev: Exclude AP jump table related code for SEV-SNP guests

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Date: Mon,  8 Apr 2024 09:40:49 +0200
From: vsntk18@...il.com
To: x86@...nel.org
Cc: cfir@...gle.com,
	dan.j.williams@...el.com,
	dave.hansen@...ux.intel.com,
	ebiederm@...ssion.com,
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	Dhaval.Giani@....com
Subject: [PATCH v5 10/10] x86/sev: Exclude AP jump table related code for SEV-SNP guests

From: Vasant Karasulli <vkarasulli@...e.de>

Unlike SEV-ES, AP jump table technique is not used in SEV-SNP
when transitioning from one layer of code to another
(e.g. when going from UEFI to the OS).

Signed-off-by: Vasant Karasulli <vkarasulli@...e.de>
---
 arch/x86/kernel/sev.c    | 6 +++++-
 arch/x86/realmode/init.c | 5 +++--
 2 files changed, 8 insertions(+), 3 deletions(-)

diff --git a/arch/x86/kernel/sev.c b/arch/x86/kernel/sev.c
index aa53e8eb4cd5..d915d9158926 100644
--- a/arch/x86/kernel/sev.c
+++ b/arch/x86/kernel/sev.c
@@ -1392,7 +1392,8 @@ STACK_FRAME_NON_STANDARD(sev_jumptable_ap_park);
 void sev_es_stop_this_cpu(void)
 {
 	if (!(cc_vendor == CC_VENDOR_AMD) ||
-	    !cc_platform_has(CC_ATTR_GUEST_STATE_ENCRYPT))
+	    !cc_platform_has(CC_ATTR_GUEST_STATE_ENCRYPT) ||
+	     cc_platform_has(CC_ATTR_GUEST_SEV_SNP))
 		return;

 	/* Only park in the AP jump table when the code has been installed */
@@ -1468,6 +1469,9 @@ bool sev_kexec_supported(void)
 	if (!cc_platform_has(CC_ATTR_GUEST_STATE_ENCRYPT))
 		return true;

+	if (cc_platform_has(CC_ATTR_GUEST_SEV_SNP))
+		return false;
+
 	/*
 	 * KEXEC with SEV-ES and more than one CPU is only supported
 	 * when the AP jump table is installed.
diff --git a/arch/x86/realmode/init.c b/arch/x86/realmode/init.c
index f9bc444a3064..ed798939be5d 100644
--- a/arch/x86/realmode/init.c
+++ b/arch/x86/realmode/init.c
@@ -80,8 +80,9 @@ static void __init sme_sev_setup_real_mode(struct trampoline_header *th)
 		 */
 		th->start = (u64) secondary_startup_64_no_verify;

-		if (sev_es_setup_ap_jump_table(real_mode_header))
-			panic("Failed to get/update SEV-ES AP Jump Table");
+		if (!cc_platform_has(CC_ATTR_GUEST_SEV_SNP))
+			if (sev_es_setup_ap_jump_table(real_mode_header))
+				panic("Failed to get/update SEV-ES AP Jump Table");
 	}
 #endif
 }
--
2.34.1