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

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Date:	Mon, 23 Aug 2010 19:11:11 +0800
From:	Xiaotian Feng <xtfeng@...il.com>
To:	Avi Kivity <avi@...hat.com>
Cc:	Tim Pepper <lnxninja@...ux.vnet.ibm.com>,
	Marcelo Tosatti <mtosatti@...hat.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 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)


> --
> error compiling committee.c: too many arguments to function
>
> --
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