linux-kernel - Re: [PATCH 3.17 100/141] x86, microcode: Fix accessing dis_ucode

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Date:	Tue, 25 Nov 2014 22:17:08 +0100
From:	Borislav Petkov <bp@...e.de>
To:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
Cc:	Boris Ostrovsky <boris.ostrovsky@...cle.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	linux-kernel@...r.kernel.org, stable@...r.kernel.org,
	Richard Hendershot <rshendershot@...si.com>,
	David Vrabel <david.vrabel@...rix.com>
Subject: Re: [PATCH 3.17 100/141] x86, microcode: Fix accessing dis_ucode_ldr
 on 32-bit

On Tue, Nov 25, 2014 at 03:36:34PM -0500, Konrad Rzeszutek Wilk wrote:
> Is there an use-case for this in virtualization at all?

Not that I know of...

> Why not make it in general then? Like:
> 
> if (cpu_has_hypervisor)
> 	return;

Ah, good idea. Although we need to do it by-foot because the cpu_has
stuff hasn't been initialized yet that early. Boris, I'm guessing
something that should work... ?

---
diff --git a/arch/x86/kernel/cpu/microcode/core_early.c b/arch/x86/kernel/cpu/microcode/core_early.c
index 2c017f242a78..77137b317e2a 100644
--- a/arch/x86/kernel/cpu/microcode/core_early.c
+++ b/arch/x86/kernel/cpu/microcode/core_early.c
@@ -74,6 +74,16 @@ static int x86_family(void)
 	return x86;
 }
 
+static bool x86_guest(void)
+{
+	u32 eax = 0x1;
+	u32 ebx, ecx = 0, edx;
+
+	native_cpuid(&eax, &ebx, &ecx, &edx);
+
+	return !!(ecx & BIT(31));
+}
+
 static bool __init check_loader_disabled_bsp(void)
 {
 #ifdef CONFIG_X86_32
@@ -98,6 +108,9 @@ void __init load_ucode_bsp(void)
 {
 	int vendor, x86;
 
+	if (x86_guest())
+		return;
+
 	if (check_loader_disabled_bsp())
 		return;
 
@@ -134,6 +147,9 @@ void load_ucode_ap(void)
 {
 	int vendor, x86;
 
+	if (x86_guest())
+		return;
+
 	if (check_loader_disabled_ap())
 		return;

-- 
Regards/Gruss,
    Boris.

Sent from a fat crate under my desk. Formatting is fine.
--
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