linux-kernel - Re: [PATCH 0/4 v2] kvm: rework KVM mmu

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Date:	Tue, 24 Aug 2010 17:50:20 +0800
From:	Xiaotian Feng <xtfeng@...il.com>
To:	Marcelo Tosatti <mtosatti@...hat.com>
Cc:	Avi Kivity <avi@...hat.com>,
	Tim Pepper <lnxninja@...ux.vnet.ibm.com>,
	Lai Jiangshan <laijs@...fujitsu.com>,
	Dave Hansen <dave@...ux.vnet.ibm.com>,
	LKML <linux-kernel@...r.kernel.org>, kvm@...r.kernel.org
Subject: Re: [PATCH 0/4 v2] kvm: rework KVM mmu_shrink() code

On Tue, Aug 24, 2010 at 10:07 AM, Marcelo Tosatti <mtosatti@...hat.com> wrote:
> On Mon, Aug 23, 2010 at 07:11:11PM +0800, Xiaotian Feng wrote:
>> On Mon, Aug 23, 2010 at 6:27 PM, Avi Kivity <avi@...hat.com> wrote:
>> >  On 08/23/2010 01:22 PM, Avi Kivity wrote:
>> >>
>> >>
>> >> I see a lot of soft lockups with this patchset:
>> >
>> > This is running the emulator.flat test case, with shadow paging.  This test
>> > triggers a lot (millions) of mmu mode switches.
>> >
>>
>> Does following patch fix your issue?
>>
>> Latest kvm mmu_shrink code rework makes kernel changes
>> kvm->arch.n_used_mmu_pages/
>> kvm->arch.n_max_mmu_pages at kvm_mmu_free_page/kvm_mmu_alloc_page,
>> which is called
>> by kvm_mmu_commit_zap_page. So the kvm->arch.n_used_mmu_pages or
>> kvm_mmu_available_pages(vcpu->kvm) is unchanged after kvm_mmu_commit_zap_page(),
>> This caused kvm_mmu_change_mmu_pages/__kvm_mmu_free_some_pages looping forever.
>> Moving kvm_mmu_commit_zap_page would make the while loop performs as normal.
>>
>> ---
>> diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
>> index f52a965..7e09a21 100644
>> --- a/arch/x86/kvm/mmu.c
>> +++ b/arch/x86/kvm/mmu.c
>> @@ -1726,8 +1726,8 @@ void kvm_mmu_change_mmu_pages(struct kvm *kvm,
>> unsigned int goal_nr_mmu_pages)
>>                                             struct kvm_mmu_page, link);
>>                         kvm_mmu_prepare_zap_page(kvm, page,
>>                                                                &invalid_list);
>> +                       kvm_mmu_commit_zap_page(kvm, &invalid_list);
>>                 }
>> -               kvm_mmu_commit_zap_page(kvm, &invalid_list);
>>                 goal_nr_mmu_pages = kvm->arch.n_used_mmu_pages;
>>         }
>>
>> @@ -2976,9 +2976,9 @@ void __kvm_mmu_free_some_pages(struct kvm_vcpu *vcpu)
>>                 sp = container_of(vcpu->kvm->arch.active_mmu_pages.prev,
>>                                   struct kvm_mmu_page, link);
>>                 kvm_mmu_prepare_zap_page(vcpu->kvm, sp, &invalid_list);
>> +               kvm_mmu_commit_zap_page(vcpu->kvm, &invalid_list);
>>                 ++vcpu->kvm->stat.mmu_recycled;
>>         }
>> -       kvm_mmu_commit_zap_page(vcpu->kvm, &invalid_list);
>>  }
>>
>>  int kvm_mmu_page_fault(struct kvm_vcpu *vcpu, gva_t cr2, u32 error_code)
>
> Please resend with a signed-off-by, and proper subject for the patch.

It's available at: https://patchwork.kernel.org/patch/125431/

Thanks
Xiaotian

>
> Thanks
>
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