From: "Borislav Petkov (AMD)" <bp@alien8.de>

On machines which don't have microcode applied yet, the revision is 0.
However, this doesn't work with the Zen family/model/stepping patch
arithmetic. So move the fixup to the patch level getter function and
this way make sure the patch level is always proper and thus the
arithmetic always works.

Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
---
 arch/x86/kernel/cpu/microcode/amd.c | 9 ++++-----
 1 file changed, 4 insertions(+), 5 deletions(-)

diff --git a/arch/x86/kernel/cpu/microcode/amd.c b/arch/x86/kernel/cpu/microcode/amd.c
index e533881284a1..f03890eec333 100644
--- a/arch/x86/kernel/cpu/microcode/amd.c
+++ b/arch/x86/kernel/cpu/microcode/amd.c
@@ -233,11 +233,6 @@ static bool need_sha_check(u32 cur_rev)
 {
 	u32 cutoff;
 
-	if (!cur_rev) {
-		cur_rev = cpuid_to_ucode_rev(bsp_cpuid_1_eax);
-		pr_info_once("No current revision, generating the lowest one: 0x%x\n", cur_rev);
-	}
-
 	cutoff = get_cutoff_revision(cur_rev);
 	if (cutoff)
 		return cur_rev <= cutoff;
@@ -338,6 +333,10 @@ static u32 get_patch_level(void)
 	}
 
 	native_rdmsr(MSR_AMD64_PATCH_LEVEL, rev, dummy);
+	if (!rev) {
+		rev = cpuid_to_ucode_rev(bsp_cpuid_1_eax);
+		pr_info_once("No current revision, generating the lowest one: 0x%x\n", rev);
+	}
 
 	return rev;
 }
-- 
2.53.0

On Fri, May 29, 2026 at 07:42:13PM -0700, Borislav Petkov wrote:
> From: "Borislav Petkov (AMD)" <bp@alien8.de>
> 
> On machines which don't have microcode applied yet, the revision is 0.
> However, this doesn't work with the Zen family/model/stepping patch
> arithmetic. So move the fixup to the patch level getter function and
> this way make sure the patch level is always proper and thus the
> arithmetic always works.
> 
> Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
> ---
>  arch/x86/kernel/cpu/microcode/amd.c | 9 ++++-----
>  1 file changed, 4 insertions(+), 5 deletions(-)

AI review caught something, here's v2:

---
From: "Borislav Petkov (AMD)" <bp@alien8.de>
Date: Fri, 29 May 2026 17:27:24 -0700
Subject: [PATCH -v2] x86/microcode/AMD: Move the no-revision fixup to get_patch_level()

On machines which don't have microcode applied yet, the revision is 0.
However, this doesn't work with the Zen family/model/stepping patch
arithmetic. So move the fixup to the patch level getter function and
this way make sure the patch level is always proper and thus the
arithmetic always works.

And now that it can be called on any family, make this Zen-only.

Assisted-by: claude/claude-opus-4-6
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
---
 arch/x86/kernel/cpu/microcode/amd.c | 12 +++++++-----
 1 file changed, 7 insertions(+), 5 deletions(-)

diff --git a/arch/x86/kernel/cpu/microcode/amd.c b/arch/x86/kernel/cpu/microcode/amd.c
index e533881284a1..b90af74b8be9 100644
--- a/arch/x86/kernel/cpu/microcode/amd.c
+++ b/arch/x86/kernel/cpu/microcode/amd.c
@@ -233,11 +233,6 @@ static bool need_sha_check(u32 cur_rev)
 {
 	u32 cutoff;
 
-	if (!cur_rev) {
-		cur_rev = cpuid_to_ucode_rev(bsp_cpuid_1_eax);
-		pr_info_once("No current revision, generating the lowest one: 0x%x\n", cur_rev);
-	}
-
 	cutoff = get_cutoff_revision(cur_rev);
 	if (cutoff)
 		return cur_rev <= cutoff;
@@ -338,6 +333,13 @@ static u32 get_patch_level(void)
 	}
 
 	native_rdmsr(MSR_AMD64_PATCH_LEVEL, rev, dummy);
+	if (!rev) {
+		if (x86_family(bsp_cpuid_1_eax) < 0x17)
+			return rev;
+
+		rev = cpuid_to_ucode_rev(bsp_cpuid_1_eax);
+		pr_info_once("No current revision, generating the lowest one: 0x%x\n", rev);
+	}
 
 	return rev;
 }
-- 
2.53.0

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette