Re: [PATCH 2/7] KVM: X86: Synchronize the shadow pagetable before link it

[Lai Jiangshan <laijs@linux.alibaba.com>]

On 2021/9/4 00:06, 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..2ff123ec0d64 100644
> --- a/arch/x86/kvm/mmu/paging_tmpl.h
> +++ b/arch/x86/kvm/mmu/paging_tmpl.h
> @@ -704,6 +704,9 @@ 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 &&
> +			    mmu_sync_children(vcpu, sp, false))
> +				return RET_PF_RETRY;

It was like my first (unsent) fix.  Just return RET_PF_RETRY when break.

And then I thought that it'd be better to retry fetching directly rather than
retry guest when the conditions are still valid/unchanged to avoid all the
next guest page walking and GUP().  Although the code does not check all
conditions such as interrupt event pending. (we can add that too)

I think it is a good design to allow break mmu_lock when mmu is handling
heavy work.


>   		}
> 
>   		/*
> --
>