linux-kernel - Re: [PATCH] mmu_notifier, kvm: Introduce dirty bit tracking in spte and mmu notifier to help KSM dirty bit tracking

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Date:	Wed, 22 Jun 2011 09:15:51 +0300
From:	Izik Eidus <izik.eidus@...ellosystems.com>
To:	Chris Wright <chrisw@...s-sol.org>
CC:	Nai Xia <nai.xia@...il.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Hugh Dickins <hughd@...gle.com>,
	Rik van Riel <riel@...hat.com>,
	linux-mm <linux-mm@...ck.org>,
	Johannes Weiner <hannes@...xchg.org>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	kvm <kvm@...r.kernel.org>, mtosatti@...hat.com
Subject: Re: [PATCH] mmu_notifier, kvm: Introduce dirty bit tracking in spte
 and mmu notifier to help KSM dirty bit tracking

On 6/22/2011 3:21 AM, Chris Wright wrote:
> * Nai Xia (nai.xia@...il.com) wrote:
>> Introduced kvm_mmu_notifier_test_and_clear_dirty(), kvm_mmu_notifier_dirty_update()
>> and their mmu_notifier interfaces to support KSM dirty bit tracking, which brings
>> significant performance gain in volatile pages scanning in KSM.
>> Currently, kvm_mmu_notifier_dirty_update() returns 0 if and only if intel EPT is
>> enabled to indicate that the dirty bits of underlying sptes are not updated by
>> hardware.
> Did you test with each of EPT, NPT and shadow?
>
>> Signed-off-by: Nai Xia<nai.xia@...il.com>
>> Acked-by: Izik Eidus<izik.eidus@...ellosystems.com>
>> ---
>>   arch/x86/include/asm/kvm_host.h |    1 +
>>   arch/x86/kvm/mmu.c              |   36 +++++++++++++++++++++++++++++
>>   arch/x86/kvm/mmu.h              |    3 +-
>>   arch/x86/kvm/vmx.c              |    1 +
>>   include/linux/kvm_host.h        |    2 +-
>>   include/linux/mmu_notifier.h    |   48 +++++++++++++++++++++++++++++++++++++++
>>   mm/mmu_notifier.c               |   33 ++++++++++++++++++++++++++
>>   virt/kvm/kvm_main.c             |   27 ++++++++++++++++++++++
>>   8 files changed, 149 insertions(+), 2 deletions(-)
>>
>> diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
>> index d2ac8e2..f0d7aa0 100644
>> --- a/arch/x86/include/asm/kvm_host.h
>> +++ b/arch/x86/include/asm/kvm_host.h
>> @@ -848,6 +848,7 @@ extern bool kvm_rebooting;
>>   int kvm_unmap_hva(struct kvm *kvm, unsigned long hva);
>>   int kvm_age_hva(struct kvm *kvm, unsigned long hva);
>>   int kvm_test_age_hva(struct kvm *kvm, unsigned long hva);
>> +int kvm_test_and_clear_dirty_hva(struct kvm *kvm, unsigned long hva);
>>   void kvm_set_spte_hva(struct kvm *kvm, unsigned long hva, pte_t pte);
>>   int cpuid_maxphyaddr(struct kvm_vcpu *vcpu);
>>   int kvm_cpu_has_interrupt(struct kvm_vcpu *vcpu);
>> diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
>> index aee3862..a5a0c51 100644
>> --- a/arch/x86/kvm/mmu.c
>> +++ b/arch/x86/kvm/mmu.c
>> @@ -979,6 +979,37 @@ out:
>>   	return young;
>>   }
>>
>> +/*
>> + * Caller is supposed to SetPageDirty(), it's not done inside this.
>> + */
>> +static
>> +int kvm_test_and_clear_dirty_rmapp(struct kvm *kvm, unsigned long *rmapp,
>> +				   unsigned long data)
>> +{
>> +	u64 *spte;
>> +	int dirty = 0;
>> +
>> +	if (!shadow_dirty_mask) {
>> +		WARN(1, "KVM: do NOT try to test dirty bit in EPT\n");
>> +		goto out;
>> +	}
> This should never fire with the dirty_update() notifier test, right?
> And that means that this whole optimization is for the shadow mmu case,
> arguably the legacy case.
>

Hi Chris,
AMD npt does track the dirty bit in the nested page tables,
so the shadow_dirty_mask should not be 0 in that case...
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