Re: [PATCH 27/28] KVM: x86/mmu: Do remote TLB flush before dropping RCU in TDP MMU resched

Subject: Re: [PATCH 27/28] KVM: x86/mmu: Do remote TLB flush before dropping RCU in TDP MMU resched
From: Paolo Bonzini <pbonzini@xxxxxxxxxx>
Date: Tue, 30 Nov 2021 12:29:36 +0100
Cc: Vitaly Kuznetsov <vkuznets@xxxxxxxxxx>, Wanpeng Li <wanpengli@xxxxxxxxxxx>, Jim Mattson <jmattson@xxxxxxxxxx>, Joerg Roedel <joro@xxxxxxxxxx>, kvm@xxxxxxxxxxxxxxx, linux-kernel@xxxxxxxxxxxxxxx, Hou Wenlong <houwenlong93@xxxxxxxxxxxxxxxxx>, Ben Gardon <bgardon@xxxxxxxxxx>
In-reply-to: <20211120045046.3940942-28-seanjc@google.com>
References: <20211120045046.3940942-1-seanjc@google.com> <20211120045046.3940942-28-seanjc@google.com>
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.2.0

On 11/20/21 05:50, Sean Christopherson wrote:

  	if (need_resched() || rwlock_needbreak(&kvm->mmu_lock)) {
-		rcu_read_unlock();
-
  		if (flush)
  			kvm_flush_remote_tlbs(kvm);

+ rcu_read_unlock();

Couldn't this sleep in kvm_make_all_cpus_request, whilst in an RCUread-side critical section?


Paolo

Follow-Ups:
- Re: [PATCH 27/28] KVM: x86/mmu: Do remote TLB flush before dropping RCU in TDP MMU resched
  - From: Sean Christopherson

References:
- [PATCH 00/28] KVM: x86/mmu: Overhaul TDP MMU zapping and flushing
  - From: Sean Christopherson
- [PATCH 27/28] KVM: x86/mmu: Do remote TLB flush before dropping RCU in TDP MMU resched
  - From: Sean Christopherson