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

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Date:	Tue, 2 Jun 2015 20:31:58 +0300
From:	Andy Shevchenko <andy.shevchenko@...il.com>
To:	Borislav Petkov <bp@...e.de>
Cc:	Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
	Ingo Molnar <mingo@...nel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Mika Westerberg <mika.westerberg@...ux.intel.com>
Subject: Re: [PATCH 1/1] x86/microcode: vsnprintf() might be unavailable

On Tue, Jun 2, 2015 at 8:00 PM, Borislav Petkov <bp@...e.de> wrote:
> On Tue, Jun 02, 2015 at 07:49:53PM +0300, Andy Shevchenko wrote:
>> Initial paging setup is involved?
>
> Yes, load_ucode_bsp happens before paging is enabled on 32-bit. And
> that should remain that way - we want microcode application as early as
> possible.
>
>> Hmm… which Intel CPUs you run on?
>
> processor       : 0
> vendor_id       : GenuineIntel
> cpu family      : 6
> model           : 58
> model name      : Intel(R) Core(TM) i7-3520M CPU @ 2.90GHz
> stepping        : 9
> microcode       : 0x1b
>
> and an SNB one too.

Now at home already.
Will check tomorrow what we have.

>
>> Ah, one more thing we run our kernel from kexec (I hope it's not a
>> case, but who knows).
>
> Does it work when you boot a normal 32-bit kernel with builtin microcode
> on it?

Ditto.

>
> In order to load built-in microcode, you'll have to enable the boot
> options in the commit message to
>
>   760d765b2bb6 ("x86/microcode: Parse built-in microcode early")
>
> Let me know if something's not clear.

We are using slightly different (to upstream) i386_defconfig with some
devices enabled like serial console. As environment the Buildroot is
used with uclibc and busybox. No extra microcode is enabled.

By default as far as I remember the FIRMWARE* is set to y for all options.

> On Tue, Jun 02, 2015 at 07:46:29PM +0300, Andy Shevchenko wrote:
>> > @@ -533,7 +533,12 @@ static bool __init load_builtin_intel_microcode(struct cpio_data *cp)
>> >     model    = x86_model(eax);
>> >     stepping = eax & 0xf;
>> >
>> > -   sprintf(name, "intel-ucode/%02x-%02x-%02x", family, model, stepping);
>> > +   *p++ = '/';
>> > +   p = hex_byte_pack(p, family);
>> > +   *p++ = '-';
>> > +   p = hex_byte_pack(p, model);
>> > +   *p++ = '-';
>> > +   p = hex_byte_pack(p, stepping);
>> >
>>
>> Forgot to add *p = '\0'; here, but it doesn't really mater for the idea.
>>
>> What I would like to tell that if I move 'call load_ucode_bsp' after
>> paging is done, it seems sprintf() starts working nicely.
>
> Hmm, ok, so something's not able to stomach pre-paging. Can you dump
> something from the failure, RIP, stack, whatever?

I have a totally empty screen (serial console). So, if you teach me
how to gather that I could do it later on.

>
> Can I reproduce it?

I can send our defconfig and kexec command line for sure.

[]

>>  and wondering if we need to fix AMD part.
>
> No need, AFAICT. It did work in my testing.

Ok. We have no AMD here :-)

-- 
With Best Regards,
Andy Shevchenko
--
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