Re: [PATCH v2 0/4] KVM: VMX: enable LBR virtualization

From: Jian Zhou
Date: Thu Nov 12 2015 - 03:18:29 EST

On 2015/11/11 23:23, Paolo Bonzini wrote:

On 23/10/2015 11:15, Jian Zhou wrote:
Changelog in v2:
(1) move the implementation into vmx.c
(2) migraton is supported
(3) add arrays in kvm_vcpu_arch struct to save/restore
LBR MSRs at vm exit/entry time.
(4) add a parameter of kvm_intel module to permanently
disable LBRV
(5) table of supported CPUs is reorgnized, LBRV
can be enabled or not according to the guest CPUID

Jian Zhou (4):
KVM: X86: Add arrays to save/restore LBR MSRs
KVM: X86: LBR MSRs of supported CPU types
KVM: X86: Migration is supported
KVM: VMX: details of LBR virtualization implementation

arch/x86/include/asm/kvm_host.h | 26 ++++-
arch/x86/include/asm/msr-index.h | 26 ++++-
arch/x86/kvm/vmx.c | 245 +++++++++++++++++++++++++++++++++++++++
arch/x86/kvm/x86.c | 88 ++++++++++++--
4 files changed, 366 insertions(+), 19 deletions(-)

Thanks, this looks better!

The reason why it took me so long to review it, is that I wanted to
understand what happens if you're running this on CPU model x but using
CPU model y for the guest. I still haven't grokked that fully, so I'll
apply your patches locally and play with them.

Yes, that is a good question. I plan to write a kernel module in the
guest to read/write the MSR_IA32_DEBUGCTLMSR and MSRs of LBR
stack with host CPU model e.g. SandyBridge while using guest CPU
model e.g. core2duo for the guest. (The address of MSRs recording
last branch information between SandyBridge and core2duo is different)

In the meanwhile, feel free to send v3 with: 1) the tweak I suggested to
patch 3; 2) the fix for the problem that the buildbot reported on patch 1.

Okay, will fix them in v3.




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