linux-kernel - [PATCH] x86/microcode/AMD: Attempt applying on every logical thread

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Date:   Sun, 14 Aug 2022 14:00:26 +0200
From:   Borislav Petkov <bp@...en8.de>
To:     X86 ML <x86@...nel.org>
Cc:     Andrew Cooper <amc96@...f.net>,
        LKML <linux-kernel@...r.kernel.org>,
        Ștefan Talpalaru <stefantalpalaru@...oo.com>
Subject: [PATCH] x86/microcode/AMD: Attempt applying on every logical thread

From: Borislav Petkov <bp@...e.de>

Currently, the patch application logic checks whether patch application
is needed. Therefore, on SMT designs where the microcode engine is
shared between the two threads, the application happens only on one of
them.

However, there are microcode patches which do per-thread modification,
see Link tag below.

Therefore, drop the revision check and try applying on each thread. This
is what the BIOS does too so this method is very much tested.

Reported-by:  Ștefan Talpalaru <stefantalpalaru@...oo.com>
Tested-by:  Ștefan Talpalaru <stefantalpalaru@...oo.com>
Signed-off-by: Borislav Petkov <bp@...e.de>
Link: https://bugzilla.kernel.org/show_bug.cgi?id=216211
---
 arch/x86/kernel/cpu/microcode/amd.c | 39 +++++++----------------------
 1 file changed, 9 insertions(+), 30 deletions(-)

diff --git a/arch/x86/kernel/cpu/microcode/amd.c b/arch/x86/kernel/cpu/microcode/amd.c
index 8b2fcdfa6d31..a575dbb4d80c 100644
--- a/arch/x86/kernel/cpu/microcode/amd.c
+++ b/arch/x86/kernel/cpu/microcode/amd.c
@@ -420,8 +420,8 @@ apply_microcode_early_amd(u32 cpuid_1_eax, void *ucode, size_t size, bool save_p
 	struct cont_desc desc = { 0 };
 	u8 (*patch)[PATCH_MAX_SIZE];
 	struct microcode_amd *mc;
-	u32 rev, dummy, *new_rev;
 	bool ret = false;
+	u32 *new_rev;
 
 #ifdef CONFIG_X86_32
 	new_rev = (u32 *)__pa_nodebug(&ucode_new_rev);
@@ -439,10 +439,6 @@ apply_microcode_early_amd(u32 cpuid_1_eax, void *ucode, size_t size, bool save_p
 	if (!mc)
 		return ret;
 
-	native_rdmsr(MSR_AMD64_PATCH_LEVEL, rev, dummy);
-	if (rev >= mc->hdr.patch_id)
-		return ret;
-
 	if (!__apply_microcode_amd(mc)) {
 		*new_rev = mc->hdr.patch_id;
 		ret      = true;
@@ -516,7 +512,7 @@ void load_ucode_amd_ap(unsigned int cpuid_1_eax)
 {
 	struct microcode_amd *mc;
 	struct cpio_data cp;
-	u32 *new_rev, rev, dummy;
+	u32 *new_rev;
 
 	if (IS_ENABLED(CONFIG_X86_32)) {
 		mc	= (struct microcode_amd *)__pa_nodebug(amd_ucode_patch);
@@ -526,10 +522,8 @@ void load_ucode_amd_ap(unsigned int cpuid_1_eax)
 		new_rev = &ucode_new_rev;
 	}
 
-	native_rdmsr(MSR_AMD64_PATCH_LEVEL, rev, dummy);
-
 	/* Check whether we have saved a new patch already: */
-	if (*new_rev && rev < mc->hdr.patch_id) {
+	if (*new_rev) {
 		if (!__apply_microcode_amd(mc)) {
 			*new_rev = mc->hdr.patch_id;
 			return;
@@ -571,23 +565,17 @@ int __init save_microcode_in_initrd_amd(unsigned int cpuid_1_eax)
 
 void reload_ucode_amd(void)
 {
-	struct microcode_amd *mc;
-	u32 rev, dummy __always_unused;
-
-	mc = (struct microcode_amd *)amd_ucode_patch;
+	struct microcode_amd *mc = (struct microcode_amd *)amd_ucode_patch;
 
-	rdmsr(MSR_AMD64_PATCH_LEVEL, rev, dummy);
-
-	if (rev < mc->hdr.patch_id) {
-		if (!__apply_microcode_amd(mc)) {
-			ucode_new_rev = mc->hdr.patch_id;
-			pr_info("reload patch_level=0x%08x\n", ucode_new_rev);
-		}
+	if (!__apply_microcode_amd(mc)) {
+		ucode_new_rev = mc->hdr.patch_id;
+		pr_info("reload patch_level=0x%08x\n", ucode_new_rev);
 	}
 }
 static u16 __find_equiv_id(unsigned int cpu)
 {
 	struct ucode_cpu_info *uci = ucode_cpu_info + cpu;
+
 	return find_equiv_id(&equiv_table, uci->cpu_sig.sig);
 }
 
@@ -678,7 +666,7 @@ static enum ucode_state apply_microcode_amd(int cpu)
 	struct ucode_cpu_info *uci;
 	struct ucode_patch *p;
 	enum ucode_state ret;
-	u32 rev, dummy __always_unused;
+	u32 rev;
 
 	BUG_ON(raw_smp_processor_id() != cpu);
 
@@ -691,14 +679,6 @@ static enum ucode_state apply_microcode_amd(int cpu)
 	mc_amd  = p->data;
 	uci->mc = p->data;
 
-	rdmsr(MSR_AMD64_PATCH_LEVEL, rev, dummy);
-
-	/* need to apply patch? */
-	if (rev >= mc_amd->hdr.patch_id) {
-		ret = UCODE_OK;
-		goto out;
-	}
-
 	if (__apply_microcode_amd(mc_amd)) {
 		pr_err("CPU%d: update failed for patch_level=0x%08x\n",
 			cpu, mc_amd->hdr.patch_id);
@@ -710,7 +690,6 @@ static enum ucode_state apply_microcode_amd(int cpu)
 
 	pr_info("CPU%d: new patch_level=0x%08x\n", cpu, rev);
 
-out:
 	uci->cpu_sig.rev = rev;
 	c->microcode	 = rev;
 
-- 
2.35.1