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SubjectRe: [PATCH 2/7] KVM: X86: Synchronize the shadow pagetable before link it
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On 2021/9/3 07:54, Sean Christopherson wrote:
>
> trace_get_page:
> diff --git a/arch/x86/kvm/mmu/paging_tmpl.h b/arch/x86/kvm/mmu/paging_tmpl.h
> index 50ade6450ace..5b13918a55c2 100644
> --- a/arch/x86/kvm/mmu/paging_tmpl.h
> +++ b/arch/x86/kvm/mmu/paging_tmpl.h
> @@ -704,6 +704,10 @@ static int FNAME(fetch)(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault,
> access = gw->pt_access[it.level - 2];
> sp = kvm_mmu_get_page(vcpu, table_gfn, fault->addr,
> it.level-1, false, access);
> + if (sp->unsync_children) {
> + kvm_make_all_cpus_request(KVM_REQ_MMU_SYNC, vcpu);
> + return RET_PF_RETRY;

Making KVM_REQ_MMU_SYNC be able remotely is good idea.
But if the sp is not linked, the @sp might not be synced even we
tried many times. So we should continue to link it.

But if we continue to link it, KVM_REQ_MMU_SYNC should be extended to
sync all roots (current root and prev_roots). And maybe add a
KVM_REQ_MMU_SYNC_CURRENT for current root syncing.

It is not going to be a simple. I have a new way to sync pages
and also fix the problem, but that include several non-fix patches.

We need to fix this problem in the simplest way. In my patch
mmu_sync_children() has a @root argument. I think we can disallow
releasing the lock when @root is false. Is it OK?



> + }
> }
>
> /*
> --
>

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