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

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Message-ID: <jpgpofinhkg.fsf@linux.bootlegged.copy>
Date:   Tue, 09 May 2017 12:03:27 -0400
From:   Bandan Das <bsd@...hat.com>
To:     Paolo Bonzini <pbonzini@...hat.com>
Cc:     kvm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 0/3] nVMX: Emulated Page Modification Logging for Nested Virtualization

Paolo Bonzini <pbonzini@...hat.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(-)
>>