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

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <daa611da-8815-048b-19d1-64a53a193d91@linux.alibaba.com>
Date:   Sat, 4 Sep 2021 00:33:32 +0800
From:   Lai Jiangshan <laijs@...ux.alibaba.com>
To:     Sean Christopherson <seanjc@...gle.com>
Cc:     Lai Jiangshan <jiangshanlai@...il.com>,
        linux-kernel@...r.kernel.org, Paolo Bonzini <pbonzini@...hat.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        x86@...nel.org, "H. Peter Anvin" <hpa@...or.com>,
        Marcelo Tosatti <mtosatti@...hat.com>,
        Avi Kivity <avi@...hat.com>, kvm@...r.kernel.org
Subject: Re: [PATCH 2/7] KVM: X86: Synchronize the shadow pagetable before
 link it



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().