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

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Date:	Mon, 02 Mar 2015 10:25:34 -0500
From:	Bandan Das <bsd@...hat.com>
To:	Radim Krčmář <rkrcmar@...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

Radim Krčmář <rkrcmar@...hat.com> writes:

> 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.

There's already one - kvm_x86_ops->skip_emulated_instruction

>> >  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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