Re: [PATCH 2/2] KVM: x86: map/unmap private slots in __x86_set_memory_region

From	Radim Krčmář <rkrcmar@redhat.com>
Newsgroups	linux.kernel
Subject	Re: [PATCH 2/2] KVM: x86: map/unmap private slots in __x86_set_memory_region
Date	2015-10-13 18:50 +0200
Message-ID	<qjaVY-3T8-33@gated-at.bofh.it> (permalink)
References	<qiK5s-6T6-5@gated-at.bofh.it> <qiK5s-6T6-17@gated-at.bofh.it> <qj9ZU-2xR-17@gated-at.bofh.it> <qjaCB-3wU-1@gated-at.bofh.it>
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2015-10-13 18:28+0200, Paolo Bonzini:
> On 13/10/2015 17:39, Radim Krčmář wrote:
>> 2015-10-12 14:09+0200, Paolo Bonzini:
>>> Otherwise, two copies (one of them never used and thus bogus) are
>>> allocated for the regular and SMM address spaces.  This breaks
>>> SMM with EPT but without unrestricted guest support, because the
>>> SMM copy of the identity page map is all zeros.
>> 
>> (Have you found out why EPT+unrestricted didn't use the alternative SMM
>>  mapping as well?)
> 
> Yes, that I already knew; EPT+unrestricted uses CR0.PG=0 directly so
> it doesn't use the identity page at all.  (CR0.PG=0 w/o unrestricted
> instead runs with CR0.PG=1.  CR3 load and store exits are enabled,
> and the guest CR3 always points to the identity page map while the
> guest runs).

Thank you.

>>> +	} else {
>>> +		if (!slot->npages)
>>> +			return 0;
>>> +
>>> +		hva = 0;
>>> +	}
>>> +
>>> +	old = *slot;
>> 
>> (Assignment could be in the 'else' == !size branch, GCC would have fun.)
> 
> It would have fun _and_ warn, which is why it's not in the else branch. :)

I wondered if its "used uninitialized" analyzer got any better :)
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[PATCH 0/2] KVM: fix SMM with ept=1/unrestricted_guest=0 Paolo Bonzini <pbonzini@redhat.com> - 2015-10-12 14:10 +0200
  [PATCH 2/2] KVM: x86: map/unmap private slots in __x86_set_memory_region Paolo Bonzini <pbonzini@redhat.com> - 2015-10-12 14:10 +0200
    Re: [PATCH 2/2] KVM: x86: map/unmap private slots in  __x86_set_memory_region Radim Krčmář <rkrcmar@redhat.com> - 2015-10-13 17:50 +0200
      Re: [PATCH 2/2] KVM: x86: map/unmap private slots in  __x86_set_memory_region Paolo Bonzini <pbonzini@redhat.com> - 2015-10-13 18:30 +0200
        Re: [PATCH 2/2] KVM: x86: map/unmap private slots in  __x86_set_memory_region Radim Krčmář <rkrcmar@redhat.com> - 2015-10-13 18:50 +0200

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