linux-kernel - [PATCH 1/2] x86/microcode/AMD: Pay attention to the stepping dynamically

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Message-ID: <20241022120711.GEZxeVbw_NzT_U1Cu4@fat_crate.local>
Date: Tue, 22 Oct 2024 14:07:11 +0200
From: Borislav Petkov <bp@...en8.de>
To: Jens Axboe <axboe@...nel.dk>
Cc: Thomas Gleixner <tglx@...utronix.de>,
	the arch/x86 maintainers <x86@...nel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	"regressions@...ts.linux.dev" <regressions@...ts.linux.dev>
Subject: [PATCH 1/2] x86/microcode/AMD: Pay attention to the stepping
 dynamically

From: "Borislav Petkov (AMD)" <bp@...en8.de>
Date: Mon, 21 Oct 2024 10:27:52 +0200

Commit in Fixes changed how a microcode patch is loaded on Zen and newer
but the patch matching needs to happen with different rigidity,
depending on what is being done:

1) When the patch is added to the patches cache, the stepping must be
   ignored because the driver still supports different steppings per
   system

2) When the patch is matched for loading, then the stepping must be
   taken into account because each CPU needs the patch matching its
   stepping

Take care of that by making the matching smarter.

Fixes: 94838d230a6c ("x86/microcode/AMD: Use the family,model,stepping encoded in the patch ID")
Reported-by: Jens Axboe <axboe@...nel.dk>
Signed-off-by: Borislav Petkov (AMD) <bp@...en8.de>
Link: https://lore.kernel.org/r/91194406-3fdf-4e38-9838-d334af538f74@kernel.dk
---
 arch/x86/kernel/cpu/microcode/amd.c | 26 ++++++++++++++++++--------
 1 file changed, 18 insertions(+), 8 deletions(-)

diff --git a/arch/x86/kernel/cpu/microcode/amd.c b/arch/x86/kernel/cpu/microcode/amd.c
index f63b051f25a0..1ae36ab37fe8 100644
--- a/arch/x86/kernel/cpu/microcode/amd.c
+++ b/arch/x86/kernel/cpu/microcode/amd.c
@@ -613,16 +613,19 @@ static int __init save_microcode_in_initrd(void)
 }
 early_initcall(save_microcode_in_initrd);
 
-static inline bool patch_cpus_equivalent(struct ucode_patch *p, struct ucode_patch *n)
+static inline bool patch_cpus_equivalent(struct ucode_patch *p,
+					 struct ucode_patch *n,
+					 bool ignore_stepping)
 {
 	/* Zen and newer hardcode the f/m/s in the patch ID */
         if (x86_family(bsp_cpuid_1_eax) >= 0x17) {
 		union cpuid_1_eax p_cid = ucode_rev_to_cpuid(p->patch_id);
 		union cpuid_1_eax n_cid = ucode_rev_to_cpuid(n->patch_id);
 
-		/* Zap stepping */
-		p_cid.stepping = 0;
-		n_cid.stepping = 0;
+		if (ignore_stepping) {
+			p_cid.stepping = 0;
+			n_cid.stepping = 0;
+		}
 
 		return p_cid.full == n_cid.full;
 	} else {
@@ -644,13 +647,13 @@ static struct ucode_patch *cache_find_patch(struct ucode_cpu_info *uci, u16 equi
 	WARN_ON_ONCE(!n.patch_id);
 
 	list_for_each_entry(p, &microcode_cache, plist)
-		if (patch_cpus_equivalent(p, &n))
+		if (patch_cpus_equivalent(p, &n, false))
 			return p;
 
 	return NULL;
 }
 
-static inline bool patch_newer(struct ucode_patch *p, struct ucode_patch *n)
+static inline int patch_newer(struct ucode_patch *p, struct ucode_patch *n)
 {
 	/* Zen and newer hardcode the f/m/s in the patch ID */
         if (x86_family(bsp_cpuid_1_eax) >= 0x17) {
@@ -659,6 +662,9 @@ static inline bool patch_newer(struct ucode_patch *p, struct ucode_patch *n)
 		zp.ucode_rev = p->patch_id;
 		zn.ucode_rev = n->patch_id;
 
+		if (zn.stepping != zp.stepping)
+			return -1;
+
 		return zn.rev > zp.rev;
 	} else {
 		return n->patch_id > p->patch_id;
@@ -668,10 +674,14 @@ static inline bool patch_newer(struct ucode_patch *p, struct ucode_patch *n)
 static void update_cache(struct ucode_patch *new_patch)
 {
 	struct ucode_patch *p;
+	int ret;
 
 	list_for_each_entry(p, &microcode_cache, plist) {
-		if (patch_cpus_equivalent(p, new_patch)) {
-			if (!patch_newer(p, new_patch)) {
+		if (patch_cpus_equivalent(p, new_patch, true)) {
+			ret = patch_newer(p, new_patch);
+			if (ret < 0)
+				continue;
+			else if (!ret) {
 				/* we already have the latest patch */
 				kfree(new_patch->data);
 				kfree(new_patch);
-- 
2.43.0

-- 
Regards/Gruss,
    Boris.

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