linux-kernel - Re: [PATCH] x86/microcode: Adjust ramdisk address when accessing by virtual address

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Message-ID: <20161219233229.p5uw2thbl55o26ds@pd.tnic>
Date:   Tue, 20 Dec 2016 00:32:29 +0100
From:   Borislav Petkov <bp@...en8.de>
To:     Boris Ostrovsky <boris.ostrovsky@...cle.com>
Cc:     x86@...nel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] x86/microcode: Adjust ramdisk address when accessing by
 virtual address

On Mon, Dec 19, 2016 at 07:43:40PM +0100, Borislav Petkov wrote:
> On Mon, Dec 19, 2016 at 01:12:25PM -0500, Boris Ostrovsky wrote:
> > IIUIC find_microcode_in_initrd() is called with paging on only on Intel
> > (which is where I observed it).
> 
> Ah, that was an important fact. Yes, I can repro it now.

Ok, questions:

* does your guest relocate the ramdisk?

I.e., do you see something like this in dmesg before the splat:

[    0.000000] RAMDISK: [mem 0x7f84c000-0x7ffcffff]
[    0.000000] Allocated new RAMDISK: [mem 0x3647a000-0x36bfd9e6]
[    0.000000] Move RAMDISK from [mem 0x7f84c000-0x7ffcf9e6] to [mem 0x3647a000-0x36bfd9e6]
	       ^^^^^^^^^^^^^^

If not, then I know what happens.

Also, does it work if you change these lines:

        if (!use_pa && relocated_ramdisk)
                start = initrd_start;

to:

        if (!use_pa)
                start = initrd_start;


Because if that works, I can actually simplify that function radically.

But more tomorrow.

Thanks.

-- 
Regards/Gruss,
    Boris.

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