From: Josh Poimboeuf <jpoimboe@kernel.org>
Date: Mon, 4 Sep 2023 22:04:47 -0700
Subject: x86/srso: Don't probe microcode in a guest
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Git-commit: 02428d0366a27c2f33bc4361eb10467777804f29
Patch-mainline: v6.6-rc3
References: git-fixes
To support live migration, the hypervisor sets the "lowest common
denominator" of features. Probing the microcode isn't allowed because
any detected features might go away after a migration.
As Andy Cooper states:
"Linux must not probe microcode when virtualised. What it may see
instantaneously on boot (owing to MSR_PRED_CMD being fully passed
through) is not accurate for the lifetime of the VM."
Rely on the hypervisor to set the needed IBPB_BRTYPE and SBPB bits.
Fixes: 1b5277c0ea0b ("x86/srso: Add SRSO_NO support")
Suggested-by: Andrew Cooper <andrew.cooper3@citrix.com>
Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>
Acked-by: Borislav Petkov (AMD) <bp@alien8.de>
Link: https://lore.kernel.org/r/3938a7209606c045a3f50305d201d840e8c834c7.1693889988.git.jpoimboe@kernel.org
Acked-by: Nikolay Borisov <nik.borisov@suse.com>
---
arch/x86/kernel/cpu/amd.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/arch/x86/kernel/cpu/amd.c b/arch/x86/kernel/cpu/amd.c
index afacc48e07da..03ef962a6992 100644
--- a/arch/x86/kernel/cpu/amd.c
+++ b/arch/x86/kernel/cpu/amd.c
@@ -767,7 +767,7 @@ static void early_init_amd(struct cpuinfo_x86 *c)
if (cpu_has(c, X86_FEATURE_TOPOEXT))
smp_num_siblings = ((cpuid_ebx(0x8000001e) >> 8) & 0xff) + 1;
- if (!cpu_has(c, X86_FEATURE_IBPB_BRTYPE)) {
+ if (!cpu_has(c, X86_FEATURE_HYPERVISOR) && !cpu_has(c, X86_FEATURE_IBPB_BRTYPE)) {
if (c->x86 == 0x17 && boot_cpu_has(X86_FEATURE_AMD_IBPB))
setup_force_cpu_cap(X86_FEATURE_IBPB_BRTYPE);
else if (c->x86 >= 0x19 && !wrmsrl_safe(MSR_IA32_PRED_CMD, PRED_CMD_SBPB)) {