linux-kernel - Re: [PATCH 4/4] KVM: MMU: Don't touch unsync sp in kvm_mmu_pte

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Message-ID: <4C977CBF.6030702@redhat.com>
Date:	Mon, 20 Sep 2010 17:24:47 +0200
From:	Avi Kivity <avi@...hat.com>
To:	Xiao Guangrong <xiaoguangrong@...fujitsu.com>
CC:	Marcelo Tosatti <mtosatti@...hat.com>,
	LKML <linux-kernel@...r.kernel.org>, KVM <kvm@...r.kernel.org>
Subject: Re: [PATCH 4/4] KVM: MMU: Don't touch unsync sp in kvm_mmu_pte_write()

  On 09/20/2010 04:21 PM, Xiao Guangrong wrote:
> Gfn may have many shadow pages, when one sp need be synced, we write
> protected sp->gfn and sync this sp but we keep other shadow pages
> asynchronous
>
> So, while gfn happen page fault, let it not touches unsync page, the unsync
> page only updated at invlpg/flush TLB time
>
> @@ -3157,6 +3164,9 @@ void kvm_mmu_pte_write(struct kvm_vcpu *vcpu, gpa_t gpa,
>
>   	mask.cr0_wp = mask.cr4_pae = mask.nxe = 1;
>   	for_each_gfn_indirect_valid_sp(vcpu->kvm, sp, gfn, node) {
> +		if (sp->unsync)
> +			continue;
> +
>

Not sure this is a win.  If a gpte is updated from having p=0 to p=1 (or 
permissions upgraded), we may not have an invlpg to sync the spte, since 
the hardware doesn't require it.  With this change, we may get an extra #PF.

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

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