Re: [Qemu-devel] QEMU (no kvm) Win7 (64bit) boot error

[Stefan Weil <sw@weilnetz.de>]

Am 10.09.2012 19:20, schrieb Clemens Kolbitsch:
> On Mon, Sep 10, 2012 at 9:23 AM, Stefan Weil <sw@weilnetz.de> wrote:
>
>
> Hi Clemens,
>
> indeed, it looks like CPUID_DE fixes that BSOD with "STOP 0x0000005D ...".
> In my test scenario Windows now reboots instead of showing the BSOD.
>
> This commit added the TCG feature bit trimming which broke Windows:
>
> commit 551a2dec8fa55006a68393b9d6fb63577d2b3f1c
> Autor:    Andre Przywara <andre.przywara@amd.com>  Do Mär 11 14:39:03 2010
> Eintragender:    Aurelien Jarno <aurelien@aurel32.net>  Sa Mär 13 16:50:54
> 2010
>
> x86/cpuid: add TCG feature bit trimming
>
> In KVM we trim the user provided CPUID bits to match the host CPU's
> one. Introduce a similar feature to QEMU/TCG. Create a mask of TCG's
> capabilities and apply it to the user bits.
> This allows to let the CPU models reflect their native archetypes.
>
> Signed-off-by: Andre Przywara <andre.przywara@amd.com>
> Signed-off-by: Aurelien Jarno <aurelien@aurel32.net>
>
>
> Andre, why don't we set the requested feature bits - no matter what TCG
> provides?
> Stefan,
>
> could you tell me what QEMU ( ;-) ) HW configuration you use for your
> testing? I'm able to boot, but it still is very unstable - after a few
> seconds of running, I still run into BSODs. I think it's independent
> of the bug I was working on, but I'd like to test some more.


I run qemu-system-x86_64 (latest from git) withthe default CPU
on a 64 bit Windows 7 host. QEMU uses that host's installation:

qemu-system-x86_64 -m 1024 -snapshot -hda //PhysicalDrive/0



>
> BTW, I'm actually quite confident that the missing CPU-ID bit caused
> the 0x5D booting BSOD, since I took two kernel boot traces (one of
> QEMU stable crashing and a working VM) and the location the traces
> branched off from each other was where the CPU-ID bits were checked
> (and this one feature bit was the only thing that was not set properly
> for the check to succeed).
>
> -Clemens

CPUID_DE is part of the PENTIUM_FEATURES macro, therefore
I think it's a very old feature which was already supported by
the Pentium CPU family. No wonder Windows complains when
it is missing.

This and maybe some more bits (there is a comment 'needed for Win64'
for CPUID_MTRR, CPUID_MCA, CPUID_CLFLUSH which were also removed)
should be set in TCG mode (as they are set with KVM).

There remain two questions:

* Do we need some TCG implementation for those bits?

* Should the patch which adds CPUID_DEagain be committed
   before the other question was answered?

Any patch in this area should also be sent to qemu-stable:
this BSOD with Windows guests running on QEMU occurs rather
often (just run a search on a web search engine to get many
hits).

Regards,
Stefan