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

Marcelo Tosatti
2010-12-06T19:50:09Z

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?

Looks good to me, except comment on patch 5.