Re: [PATCH v2 0/3] nVMX: Emulated Page Modification Logging for Nested Virtualization

Bandan Das
2017-05-09T16:03:27Z

Paolo Bonzini <pbonzini@redhat.com> writes:

> On 05/05/2017 21:25, Bandan Das wrote:
>> v2:
>> 2/3: Clear out all bits except bit 12
>> 3/3: Slightly modify an existing comment, honor L0's
>> PML setting when clearing it for L1
>>
>> v1:
>> http://www.spinics.net/lists/kvm/msg149247.html
>>
>> These patches implement PML on top of EPT A/D emulation
>> (ae1e2d1082ae).
>>
>> When dirty bit is being set, we write the gpa to the
>> buffer provided by L1. If the index overflows, we just
>> change the exit reason before running L1.
>
> I tested this with api/dirty-log-perf, and nested PML is more than 3
> times faster than pml=0. I want to do a few more tests because I don't
> see any PML full exits in the L1 trace, but it seems to be a nice
> improvement!

Thanks for testing! Regarding the PML full exits, I did notice their
absence. I induced it artifically in my testing with a lower index
and it seemed to work fine.

> Paolo
>
>> Bandan Das (3):
>> kvm: x86: Add a hook for arch specific dirty logging emulation
>> nVMX: Implement emulated Page Modification Logging
>> nVMX: Advertise PML to L1 hypervisor
>>
>> arch/x86/include/asm/kvm_host.h | 2 +
>> arch/x86/kvm/mmu.c | 15 +++++++
>> arch/x86/kvm/mmu.h | 1 +
>> arch/x86/kvm/paging_tmpl.h | 4 ++
>> arch/x86/kvm/vmx.c | 97 ++++++++++++++++++++++++++++++++++++++---
>> 5 files changed, 112 insertions(+), 7 deletions(-)
>>