linux-kernel - Re: [PATCH] x86: svm: make wbinvd faster

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Date:	Mon, 2 Mar 2015 14:59:25 +0100
From:	Radim Krčmář <rkrcmar@...hat.com>
To:	Bandan Das <bsd@...hat.com>
Cc:	Joel Schopp <joel.schopp@....com>, Gleb Natapov <gleb@...nel.org>,
	Paolo Bonzini <pbonzini@...hat.com>, kvm@...r.kernel.org,
	David Kaplan <David.Kaplan@....com>,
	Joerg Roedel <joro@...tes.org>,
	Marcelo Tosatti <mtosatti@...hat.com>,
	linux-kernel@...r.kernel.org, Borislav Petkov <bp@...en8.de>
Subject: Re: [PATCH] x86: svm: make wbinvd faster

2015-03-01 21:29-0500, Bandan Das:
> Joel Schopp <joel.schopp@....com> writes:
> 
> > From: David Kaplan <David.Kaplan@....com>
> > No need to re-decode WBINVD since we know what it is from the intercept.
> >
> > Signed-off-by: David Kaplan <David.Kaplan@....com>
> > [extracted from larger unlrelated patch, forward ported, tested]
> > Signed-off-by: Joel Schopp <joel.schopp@....com>
> > ---
> > diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
> > +static int wbinvd_interception(struct vcpu_svm *svm)
> > +{
> > +	kvm_emulate_wbinvd(&svm->vcpu);
> > +	skip_emulated_instruction(&svm->vcpu);
> > +	return 1;
> > +}
> > +
> > +
> Can't we merge this to kvm_emulate_wbinvd, and just call that function
> directly for both vmx and svm ?

kvm_emulate_wbinvd() lives in x86.c and skip_emulated_instruction() is
from svm.c/vmx.c:  so we'd have to create a new x86 op and change the
emulator code as well ... it's probably better like this.

> >  static int xsetbv_interception(struct vcpu_svm *svm)
> >  {
> >  	u64 new_bv = kvm_read_edx_eax(&svm->vcpu);
> > @@ -3376,7 +3384,7 @@ static int (*const svm_exit_handlers[])(struct vcpu_svm *svm) = {
> >  	[SVM_EXIT_STGI]				= stgi_interception,
> >  	[SVM_EXIT_CLGI]				= clgi_interception,
> >  	[SVM_EXIT_SKINIT]			= skinit_interception,
> > -	[SVM_EXIT_WBINVD]                       = emulate_on_interception,
> So, this means x86_emulate_insn() in emulate.c has no callers left for the
> wbinvd case ? vmx calls kvm_emulate_wbinvd directly too..

I think that invalid state emulation might still hit wbinvd.
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