2020-04-22 08:21:47

by Evalds Iodzevics

Subject: [PATCH v2] x86/microcode/intel: replace sync_core() with native_cpuid_reg(eax)

On Intel it is required to do CPUID(1) before reading the microcode
revision MSR. Current code in 4.4 an 4.9 relies on sync_core() to call
CPUID, unfortunately on 32 bit machines code inside sync_core() always
jumps past CPUID instruction as it depends on data structure boot_cpu_data
witch are not populated correctly so early in boot sequence.

It depends on:
commit 5dedade6dfa2 ("x86/CPU: Add native CPUID variants returning a single
datum")

This patch is for 4.4 but also should apply to 4.9

Signed-off-by: Evalds Iodzevics <[email protected]>
Cc: [email protected]
---
arch/x86/include/asm/microcode_intel.h | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/include/asm/microcode_intel.h b/arch/x86/include/asm/microcode_intel.h
index 90343ba50485..92ce9c8a508b 100644
--- a/arch/x86/include/asm/microcode_intel.h
+++ b/arch/x86/include/asm/microcode_intel.h
@@ -60,7 +60,7 @@ static inline u32 intel_get_microcode_revision(void)
native_wrmsrl(MSR_IA32_UCODE_REV, 0);

/* As documented in the SDM: Do a CPUID 1 here */
- sync_core();
+ native_cpuid_eax(1);

/* get the current revision from MSR 0x8B */
native_rdmsr(MSR_IA32_UCODE_REV, dummy, rev);
--
2.17.4

2020-04-22 08:30:14

by Greg Kroah-Hartman

Subject: Re: [PATCH v2] x86/microcode/intel: replace sync_core() with native_cpuid_reg(eax)

On Wed, Apr 22, 2020 at 11:17:59AM +0300, Evalds Iodzevics wrote:
> On Intel it is required to do CPUID(1) before reading the microcode
> revision MSR. Current code in 4.4 an 4.9 relies on sync_core() to call
> CPUID, unfortunately on 32 bit machines code inside sync_core() always
> jumps past CPUID instruction as it depends on data structure boot_cpu_data
> witch are not populated correctly so early in boot sequence.
>
> It depends on:
> commit 5dedade6dfa2 ("x86/CPU: Add native CPUID variants returning a single
> datum")
>
> This patch is for 4.4 but also should apply to 4.9
>
> Signed-off-by: Evalds Iodzevics <[email protected]>
> Cc: [email protected]
> ---
> arch/x86/include/asm/microcode_intel.h | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)

Thanks, much better, now queued up.

greg k-h