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

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Message-ID: <20150310110131.GA12854@potion.brq.redhat.com>
Date:	Tue, 10 Mar 2015 12:01:31 +0100
From:	Radim Krčmář <rkrcmar@...hat.com>
To:	Marcelo Tosatti <mtosatti@...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>, linux-kernel@...r.kernel.org,
	Borislav Petkov <bp@...en8.de>
Subject: Re: [PATCH] x86: svm: make wbinvd faster

2015-03-09 20:28-0300, Marcelo Tosatti:
> On Fri, Feb 27, 2015 at 06:19:18PM -0600, Joel Schopp wrote:
> > 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>
> 
> Can't you disable the intercept if need_emulate_wbinvd(vcpu) == false? 

I don't think we want to:  it should be faster to intercept and ignore
than to invalidate all caches.  The exit doesn't affect other physical
cores and costs just about 10(?) L3 cache misses.
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