linux-kernel - [PATCH] x86/microcode/AMD: Change load_microcode

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Date:   Sun, 28 May 2017 22:04:14 +0200
From:   Borislav Petkov <bp@...en8.de>
To:     X86 ML <x86@...nel.org>
Cc:     LKML <linux-kernel@...r.kernel.org>
Subject: [PATCH] x86/microcode/AMD: Change load_microcode_amd()'s param to bool

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

With CONFIG_DEBUG_PREEMPT enabled, I get:

  BUG: using smp_processor_id() in preemptible [00000000] code: swapper/0/1
  caller is debug_smp_processor_id
  CPU: 0 PID: 1 Comm: swapper/0 Not tainted 4.12.0-rc2+ #2
  Call Trace:
   dump_stack
   check_preemption_disabled
   debug_smp_processor_id
   save_microcode_in_initrd_amd
   ? microcode_init
   save_microcode_in_initrd
   ...

because, well, it says it above, we're using smp_processor_id() in
preemptible code.

But passing the CPU number is not really needed. It is only used to
determine whether we're on the BSP, and, if so, to save the microcode
patch for early loading.

 [ We don't absolutely need to do it on the BSP but we do that
   customarily there. ]

Instead, convert that function parameter to a boolean which denotes
whether the patch should be saved or not, thereby avoiding the use of
smp_processor_id() in preemptible code.

Signed-off-by: Borislav Petkov <bp@...e.de>
---
 arch/x86/kernel/cpu/microcode/amd.c | 16 ++++++++--------
 1 file changed, 8 insertions(+), 8 deletions(-)

diff --git a/arch/x86/kernel/cpu/microcode/amd.c b/arch/x86/kernel/cpu/microcode/amd.c
index 45db4d2ebd01..e9f4d762aa5b 100644
--- a/arch/x86/kernel/cpu/microcode/amd.c
+++ b/arch/x86/kernel/cpu/microcode/amd.c
@@ -320,7 +320,7 @@ void load_ucode_amd_ap(unsigned int cpuid_1_eax)
 }
 
 static enum ucode_state
-load_microcode_amd(int cpu, u8 family, const u8 *data, size_t size);
+load_microcode_amd(bool save, u8 family, const u8 *data, size_t size);
 
 int __init save_microcode_in_initrd_amd(unsigned int cpuid_1_eax)
 {
@@ -338,8 +338,7 @@ int __init save_microcode_in_initrd_amd(unsigned int cpuid_1_eax)
 	if (!desc.mc)
 		return -EINVAL;
 
-	ret = load_microcode_amd(smp_processor_id(), x86_family(cpuid_1_eax),
-				 desc.data, desc.size);
+	ret = load_microcode_amd(true, x86_family(cpuid_1_eax), desc.data, desc.size);
 	if (ret != UCODE_OK)
 		return -EINVAL;
 
@@ -675,7 +674,7 @@ static enum ucode_state __load_microcode_amd(u8 family, const u8 *data,
 }
 
 static enum ucode_state
-load_microcode_amd(int cpu, u8 family, const u8 *data, size_t size)
+load_microcode_amd(bool save, u8 family, const u8 *data, size_t size)
 {
 	enum ucode_state ret;
 
@@ -689,8 +688,8 @@ load_microcode_amd(int cpu, u8 family, const u8 *data, size_t size)
 
 #ifdef CONFIG_X86_32
 	/* save BSP's matching patch for early load */
-	if (cpu_data(cpu).cpu_index == boot_cpu_data.cpu_index) {
-		struct ucode_patch *p = find_patch(cpu);
+	if (save) {
+		struct ucode_patch *p = find_patch(0);
 		if (p) {
 			memset(amd_ucode_patch, 0, PATCH_MAX_SIZE);
 			memcpy(amd_ucode_patch, p->data, min_t(u32, ksize(p->data),
@@ -722,11 +721,12 @@ static enum ucode_state request_microcode_amd(int cpu, struct device *device,
 {
 	char fw_name[36] = "amd-ucode/microcode_amd.bin";
 	struct cpuinfo_x86 *c = &cpu_data(cpu);
+	bool bsp = c->cpu_index == boot_cpu_data.cpu_index;
 	enum ucode_state ret = UCODE_NFOUND;
 	const struct firmware *fw;
 
 	/* reload ucode container only on the boot cpu */
-	if (!refresh_fw || c->cpu_index != boot_cpu_data.cpu_index)
+	if (!refresh_fw || !bsp)
 		return UCODE_OK;
 
 	if (c->x86 >= 0x15)
@@ -743,7 +743,7 @@ static enum ucode_state request_microcode_amd(int cpu, struct device *device,
 		goto fw_release;
 	}
 
-	ret = load_microcode_amd(cpu, c->x86, fw->data, fw->size);
+	ret = load_microcode_amd(bsp, c->x86, fw->data, fw->size);
 
  fw_release:
 	release_firmware(fw);
-- 
2.11.0