From: bluhm <bluhm@openbsd.org>
Date: Fri, 4 Oct 2024 21:15:52 +0000 (+0000)
Subject: Allow kernel boot on QEMU with AMD SEV.
X-Git-Url: http://artulab.com/gitweb/?a=commitdiff_plain;h=2ce883118e8e5b201f86b9c7b55b5710ef029134;p=openbsd

Allow kernel boot on QEMU with AMD SEV.

When booting an OpenBSD kernel on Linux QEMU with SEV enabled, the
hypervisor does not forward the SME feature, only the SEV bit is
set.  Therefore do not depend on SME when checking for SEV guest
mode in locore0.

from Sebastian Sturm; via hshoexer@; OK jsg@
---

diff --git a/sys/arch/amd64/amd64/locore0.S b/sys/arch/amd64/amd64/locore0.S
index bc45eee7a09..978821715e7 100644
--- a/sys/arch/amd64/amd64/locore0.S
+++ b/sys/arch/amd64/amd64/locore0.S
@@ -1,4 +1,4 @@
-/*	$OpenBSD: locore0.S,v 1.25 2024/07/21 19:41:31 bluhm Exp $	*/
+/*	$OpenBSD: locore0.S,v 1.26 2024/10/04 21:15:52 bluhm Exp $	*/
 /*	$NetBSD: locore.S,v 1.13 2004/03/25 18:33:17 drochner Exp $	*/
 
 /*
@@ -269,37 +269,33 @@ cont:
 	orl	%edx, RELOC(cpu_feature)
 
 	/*
-	 * Determine AMD SME and SEV capabilities.
+	 * Determine AMD SEV capability.
 	 */
 	movl	$RELOC(cpu_vendor),%ebp
 	cmpl $0x68747541, (%ebp)	/* "Auth" */
-	jne	.Lno_smesev
+	jne	.Lno_sev
 	cmpl $0x69746e65, 4(%ebp)	/* "enti" */
-	jne	.Lno_smesev
+	jne	.Lno_sev
 	cmpl $0x444d4163, 8(%ebp)	/* "cAMD" */
-	jne	.Lno_smesev
+	jne	.Lno_sev
 
-	/* AMD CPU, check for SME and SEV. */
+	/* AMD CPU, check for SEV. */
 	movl	$0x8000001f, %eax
 	cpuid
-	pushl	%eax
-	andl	$CPUIDEAX_SME, %eax	/* SME */
-	popl	%eax
-	jz	.Lno_smesev
 	andl	$CPUIDEAX_SEV, %eax	/* SEV */
-	jz	.Lno_smesev
+	jz	.Lno_sev
 
 	/* Are we in guest mode with SEV enabled? */
 	movl	$MSR_SEV_STATUS, %ecx
 	rdmsr
 	andl	$SEV_STAT_ENABLED, %eax
-	jz	.Lno_smesev
+	jz	.Lno_sev
 
 	/* Determine C bit position */
 	movl	%ebx, %ecx	/* %ebx from previous cpuid */
 	andl	$0x3f, %ecx
 	cmpl	$0x20, %ecx	/* must be at least bit 32 (counting from 0) */
-	jl	.Lno_smesev
+	jl	.Lno_sev
 	xorl	%eax, %eax
 	movl	%eax, RELOC(pg_crypt)
 	subl	$0x20, %ecx
@@ -338,7 +334,7 @@ cont:
 
 	movl	$0x1, RELOC(cpu_sev_guestmode)	/* we are a SEV guest */
 
-.Lno_smesev:
+.Lno_sev:
 
 	/*
 	 * Finished with old stack; load new %esp now instead of later so we