Re: [Qemu-devel] [PATCH 3/6] kvmvapic: Introduce TPR access optimization for Windows guests

[Jan Kiszka]

On 2012-02-09 18:20, Paolo Bonzini wrote:
> On 02/09/2012 05:32 PM, Jan Kiszka wrote:
>> >  I mean just check kpcr.self.
>>
>> Yes, clear, but that means that Windows must have initialized FS.base to
>> point to the KPCR also in UP mode. Is that really the case? E.g. when
>> ACPI is off?! I wonder if that explains the reported bug of qemu-kvm
>> with -no-acpi and in-kernel irqchip...
> 
> Yes, it does.  It's used by some fast-path kernel APIs, and indeed the
> canonical way to find the KPCR base from ring 0 is to look at FS:[1Ch].

Yep, can confirm this so far. I briefly tested a non-ACPI installation,
and it both works without problems on qemu-kvm and shows that pattern at
FS:[1C].

I guess I will simply remove the smp_cpus == 1 special case.

Jan

PS: Please strip of the newsgroups from CC when picking up a thread via
news.gmane.org. Some clients may not be configured to reply to them
(like mine - intentionally :) ).

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