linux-kernel - Re: [PATCH 1/1] x86/microcode: vsnprintf() might be unavailable

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Date:	Wed, 3 Jun 2015 23:13:52 +0200
From:	Borislav Petkov <bp@...e.de>
To:	"Shevchenko, Andriy" <andriy.shevchenko@...el.com>
Cc:	"andy.shevchenko@...il.com" <andy.shevchenko@...il.com>,
	"mingo@...nel.org" <mingo@...nel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"mika.westerberg@...ux.intel.com" <mika.westerberg@...ux.intel.com>
Subject: Re: [PATCH 1/1] x86/microcode: vsnprintf() might be unavailable

On Wed, Jun 03, 2015 at 05:49:05PM +0000, Shevchenko, Andriy wrote:
> On Wed, 2015-06-03 at 18:27 +0300, Andy Shevchenko wrote:
> > > > I have a totally empty screen (serial console). So, if you teach me
> > > > how to gather that I could do it later on.
> > > 
> > > That'll be hard - you'd probably need a hardware debugger or something
> > > special to get a RIP or other data that early... Or hack up some very
> > > early console printing with BIOS methods and so on. hpa had something
> > > like that somewhere AFAIR...
> > 
> > I could try kvm / qemu as well, though there might be not the same
> > conditions.
> 
> Yeah, qemu runs fine.

So, I did some more experiments and even if we build the string
properly, we choke later in get_builtin_firmware(). Actually, we don't
choke but we don't find firwmare because we're running with physical
addresses and those __start/__stop_builtin_fw things are virtual
addresses. Yuck!

So I'm gravitating towards disabling builtin microcode loading on
32-bit. For now, as the merge window is going to be open soon, until
we/I have fixed it properly. And I don't have a clear solution now - all
I can think of is ugly ifdeffery which I'd like to avoid.

Grrr.

---
diff --git a/arch/x86/kernel/cpu/microcode/amd_early.c b/arch/x86/kernel/cpu/microcode/amd_early.c
index 9208a36d0f03..9243cd839829 100644
--- a/arch/x86/kernel/cpu/microcode/amd_early.c
+++ b/arch/x86/kernel/cpu/microcode/amd_early.c
@@ -230,6 +230,7 @@ static void apply_ucode_in_initrd(void *ucode, size_t size, bool save_patch)
 
 static bool __init load_builtin_amd_microcode(struct cpio_data *cp, int family)
 {
+#ifdef CONFIG_X86_64
 	char fw_name[36] = "amd-ucode/microcode_amd.bin";
 
 	if (family >= 0x15)
@@ -237,6 +238,9 @@ static bool __init load_builtin_amd_microcode(struct cpio_data *cp, int family)
 			 "amd-ucode/microcode_amd_fam%.2xh.bin", family);
 
 	return get_builtin_firmware(cp, fw_name);
+#else
+	return false;
+#endif
 }
 
 void __init load_ucode_amd_bsp(int family)
diff --git a/arch/x86/kernel/cpu/microcode/intel_early.c b/arch/x86/kernel/cpu/microcode/intel_early.c
index 10dff3f3f686..b4858d892592 100644
--- a/arch/x86/kernel/cpu/microcode/intel_early.c
+++ b/arch/x86/kernel/cpu/microcode/intel_early.c
@@ -523,6 +523,7 @@ EXPORT_SYMBOL_GPL(save_mc_for_early);
 
 static bool __init load_builtin_intel_microcode(struct cpio_data *cp)
 {
+#ifdef CONFIG_X86_64
 	u32 eax = 0x00000001, ebx, ecx = 0, edx;
 	int family, model, stepping;
 	char name[30];
@@ -536,6 +537,9 @@ static bool __init load_builtin_intel_microcode(struct cpio_data *cp)
 	sprintf(name, "intel-ucode/%02x-%02x-%02x", family, model, stepping);
 
 	return get_builtin_firmware(cp, name);
+#else
+	return false;
+#endif
 }
 
 static __initdata char ucode_name[] = "kernel/x86/microcode/GenuineIntel.bin";

-- 
Regards/Gruss,
    Boris.

ECO tip #101: Trim your mails when you reply.
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