linux-kernel - [PATCH] x86/microcode: Use native_cpuid() in load_ucode_amd

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Message-Id: <1481906392-3847-1-git-send-email-boris.ostrovsky@oracle.com>
Date:   Fri, 16 Dec 2016 11:39:52 -0500
From:   Boris Ostrovsky <boris.ostrovsky@...cle.com>
To:     bp@...en8.de
Cc:     x86@...nel.org, linux-kernel@...r.kernel.org, jgross@...e.com,
        xen-devel@...ts.xenproject.org,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>
Subject: [PATCH] x86/microcode: Use native_cpuid() in load_ucode_amd_bsp()

When CONFIG_PARAVIRT is selected, cpuid() becomes a call. Since
for 32-bit kernels load_ucode_amd_bsp() is executed before paging
is enabled the call cannot be completed (as kernel virtual addresses
are not reachable yet).

Use native_cpuid() instead which is an asm wrapper for CPUID instruction.

Signed-off-by: Boris Ostrovsky <boris.ostrovsky@...cle.com>
---
 arch/x86/kernel/cpu/microcode/amd.c |    6 +++++-
 1 files changed, 5 insertions(+), 1 deletions(-)

diff --git a/arch/x86/kernel/cpu/microcode/amd.c b/arch/x86/kernel/cpu/microcode/amd.c
index 6f353bd..e2d941f 100644
--- a/arch/x86/kernel/cpu/microcode/amd.c
+++ b/arch/x86/kernel/cpu/microcode/amd.c
@@ -297,6 +297,7 @@ void __init load_ucode_amd_bsp(unsigned int family)
 	struct cpio_data cp;
 	const char *path;
 	bool use_pa;
+	u32 eax, ebx, ecx, edx;
 
 	if (IS_ENABLED(CONFIG_X86_32)) {
 		uci	= (struct ucode_cpu_info *)__pa_nodebug(ucode_cpu_info);
@@ -315,7 +316,10 @@ void __init load_ucode_amd_bsp(unsigned int family)
 		return;
 
 	/* Get BSP's CPUID.EAX(1), needed in load_microcode_amd() */
-	uci->cpu_sig.sig = cpuid_eax(1);
+	eax = 0x00000001;
+	ecx = 0;
+	native_cpuid(&eax, &ebx, &ecx, &edx);
+	uci->cpu_sig.sig = eax;
 
 	apply_microcode_early_amd(cp.data, cp.size, true);
 }
-- 
1.7.1