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From: Lai Jiangshan <laijs@linux.alibaba.com>
To: Sean Christopherson <seanjc@google.com>
Cc: Lai Jiangshan <jiangshanlai@gmail.com>,
	linux-kernel@vger.kernel.org, Paolo Bonzini <pbonzini@redhat.com>,
	Vitaly Kuznetsov <vkuznets@redhat.com>,
	Wanpeng Li <wanpengli@tencent.com>,
	Jim Mattson <jmattson@google.com>, Joerg Roedel <joro@8bytes.org>,
	Thomas Gleixner <tglx@linutronix.de>,
	Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
	x86@kernel.org, "H. Peter Anvin" <hpa@zytor.com>,
	Marcelo Tosatti <mtosatti@redhat.com>,
	Avi Kivity <avi@redhat.com>,
	kvm@vger.kernel.org
Subject: Re: [PATCH 2/7] KVM: X86: Synchronize the shadow pagetable before link it
Date: Sat, 4 Sep 2021 00:33:32 +0800	[thread overview]
Message-ID: <daa611da-8815-048b-19d1-64a53a193d91@linux.alibaba.com> (raw)
In-Reply-To: <YTJIBr/lm5QU/Z3W@google.com>



On 2021/9/4 00:06, Sean Christopherson wrote:

> -static void mmu_sync_children(struct kvm_vcpu *vcpu,
> -			      struct kvm_mmu_page *parent)
> +static int mmu_sync_children(struct kvm_vcpu *vcpu,
> +			     struct kvm_mmu_page *parent, bool can_yield)
>   {
>   	int i;
>   	struct kvm_mmu_page *sp;
> @@ -2050,7 +2050,15 @@ static void mmu_sync_children(struct kvm_vcpu *vcpu,
>   			flush |= kvm_sync_page(vcpu, sp, &invalid_list);
>   			mmu_pages_clear_parents(&parents);
>   		}
> -		if (need_resched() || rwlock_needbreak(&vcpu->kvm->mmu_lock)) {
> +		/*
> +		 * Don't yield if there are fewer than <N> unsync children
> +		 * remaining, just finish up and get out.
> +		 */
> +		if (parent->unsync_children > SOME_ARBITRARY_THRESHOLD &&
> +		    (need_resched() || rwlock_needbreak(&vcpu->kvm->mmu_lock))) {
> +			if (!can_yield)
> +				return -EINTR;
> +


Another thought about this function.

It is courtesy to break when rwlock_needbreak(), but the price is quite high,
with remote flushing to interrupt several pCPUs.  I think we can only break
when need_resched().

  parent reply	other threads:[~2021-09-03 16:33 UTC|newest]

Thread overview: 30+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-08-24  7:55 [PATCH 0/7] KVM: X86: MMU: misc fixes and cleanups Lai Jiangshan
2021-08-24  7:55 ` [PATCH 1/7] KVM: X86: Fix missed remote tlb flush in rmap_write_protect() Lai Jiangshan
2021-09-02 21:38   ` Sean Christopherson
2021-09-13  9:57   ` Maxim Levitsky
2021-08-24  7:55 ` [PATCH 2/7] KVM: X86: Synchronize the shadow pagetable before link it Lai Jiangshan
2021-09-02 23:40   ` Sean Christopherson
2021-09-02 23:54     ` Sean Christopherson
2021-09-03  0:44       ` Lai Jiangshan
2021-09-03 16:06         ` Sean Christopherson
2021-09-03 16:25           ` Lai Jiangshan
2021-09-03 16:40             ` Sean Christopherson
2021-09-03 17:00               ` Lai Jiangshan
2021-09-03 16:33           ` Lai Jiangshan [this message]
2021-09-03  0:51     ` Lai Jiangshan
2021-09-13 11:30     ` Maxim Levitsky
2021-09-13 20:49       ` Sean Christopherson
2021-09-13 22:31         ` Maxim Levitsky
2021-08-24  7:55 ` [PATCH 3/7] KVM: X86: Zap the invalid list after remote tlb flushing Lai Jiangshan
2021-09-02 21:54   ` Sean Christopherson
2021-08-24  7:55 ` [PATCH 4/7] KVM: X86: Remove FNAME(update_pte) Lai Jiangshan
2021-09-13  9:49   ` Maxim Levitsky
2021-08-24  7:55 ` [PATCH 5/7] KVM: X86: Don't unsync pagetables when speculative Lai Jiangshan
2021-09-13 11:02   ` Maxim Levitsky
2021-09-18  3:06     ` Lai Jiangshan
2021-08-24  7:55 ` [PATCH 6/7] KVM: X86: Don't check unsync if the original spte is writible Lai Jiangshan
2021-08-24  7:55 ` [PATCH 7/7] KVM: X86: Also prefetch the last range in __direct_pte_prefetch() Lai Jiangshan
2021-08-25 15:18   ` Sean Christopherson
2021-08-25 22:58     ` Lai Jiangshan
2021-08-31 18:02 ` [PATCH 0/7] KVM: X86: MMU: misc fixes and cleanups Lai Jiangshan
2021-08-31 21:57   ` Sean Christopherson

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