linux-kernel - Re: [PATCH 0/12] KVM: SVM: Add support for VMCB state caching

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Message-ID: <20101207082621.GD29502@8bytes.org>
Date:	Tue, 7 Dec 2010 09:26:21 +0100
From:	Joerg Roedel <joro@...tes.org>
To:	Marcelo Tosatti <mtosatti@...hat.com>
Cc:	Joerg Roedel <joerg.roedel@....com>, Avi Kivity <avi@...hat.com>,
	kvm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/12] KVM: SVM: Add support for VMCB state caching

On Mon, Dec 06, 2010 at 05:49:55PM -0200, Marcelo Tosatti wrote:
> On Fri, Dec 03, 2010 at 11:45:47AM +0100, Joerg Roedel wrote:
> > Hi Avi, Hi Marcelo,
> > 
> > here is a patch-set which adds support for VMCB state caching to KVM.
> > This is a new CPU feature where software can mark certain parts of the
> > VMCB as unchanged since the last vmexit and the hardware can then avoid
> > reloading these parts from memory.
> > 
> > The feature is implemented downwards-compatible in hardware, so a 0-bit
> > means the state has changed and needs to be reloaded. This makes it
> > possible to implement the bits without checking for the feature, as done
> > in this patch-set (another reason is that the check is as expensive as
> > clearing the bit). Processors which do not implement VMCB state
> > caching just ignore these bits.
> > 
> > These patches were tested with multiple guests (Windows, Linux, also in
> > parallel) and also with nested-svm.
> > 
> > The patches apply on-top of the intercept mask wrapping patch-set I sent
> > earlier this week. Your feedback is appreciated.
> > 
> > Regards,
> > 	Joerg
> > 
> >  arch/x86/include/asm/svm.h |    6 +++-
> >  arch/x86/kvm/svm.c         |   70 ++++++++++++++++++++++++++++++++++++++++++++
> >  2 files changed, 75 insertions(+), 1 deletions(-)
> > 
> > Joerg Roedel (12):
> >       KVM: SVM: Add clean-bits infrastructure code
> >       KVM: SVM: Add clean-bit for intercetps, tsc-offset and pause filter count
> >       KVM: SVM: Add clean-bit for IOPM_BASE and MSRPM_BASE
> >       KVM: SVM: Add clean-bit for the ASID
> >       KVM: SVM: Add clean-bit for interrupt state
> >       KVM: SVM: Add clean-bit for NPT state
> >       KVM: SVM: Add clean-bit for control registers
> >       KVM: SVM: Add clean-bit for DR6 and DR7
> >       KVM: SVM: Add clean-bit for GDT and IDT
> >       KVM: SVM: Add clean-bit for Segements and CPL
> >       KVM: SVM: Add clean-bit for CR2 register
> >       KVM: SVM: Add clean-bit for LBR state
> 
> Wouldnt it be good to wrap assignment of field & dirty bit update 
> in wrappers, for long term maintainability?

Right. I did that for the intercept masks already. Most other stuff is
also already wrapped. But there is certainly still room for improvement.

	Joerg

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