linux-kernel - Re: [PATCH 3/3] KVM: x86: correct mwait and monitor emulation

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Message-ID: <jpgtx7iazrs.fsf@redhat.com>
Date:	Wed, 18 Jun 2014 13:33:27 -0400
From:	Bandan Das <bsd@...hat.com>
To:	Paolo Bonzini <pbonzini@...hat.com>
Cc:	Nadav Amit <namit@...technion.ac.il>, gleb@...nel.org,
	tglx@...utronix.de, mingo@...hat.com, hpa@...or.com,
	x86@...nel.org, linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
	joro@...tes.org
Subject: Re: [PATCH 3/3] KVM: x86: correct mwait and monitor emulation

Paolo Bonzini <pbonzini@...hat.com> writes:

> Il 18/06/2014 18:43, Bandan Das ha scritto:
>>> > mwait and monitor are currently handled as nop. Considering this behavior, they
>>> > should still be handled correctly, i.e., check execution conditions and generate
>>> > exceptions when required. mwait and monitor may also be executed in real-mode
>> Is this necessary ? They are NOPs and kvm prints that out (correctly so) to dmesg.
>> Implementing them correctly is a different thing, but adding extra checks for NOPs
>> just seems like adding extra cycles.
>
> Raising the correct exception is a good thing, though.  The guest is
> going to busy wait anyway, it doesn't matter how fast it does that. :)

Thanks, makes sense. I was also thinking why to advertise it at all, but it's 
probably more common than I think it is.

> Paolo
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