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From: Paolo Bonzini <pbonzini@redhat.com>
To: Marcelo Tosatti <mtosatti@redhat.com>
Cc: kvm@vger.kernel.org, Alex Williamson <alex.williamson@redhat.com>,
	Sean Christopherson <seanjc@google.com>,
	Peter Xu <peterx@redhat.com>, Pei Zhang <pezhang@redhat.com>
Subject: Re: [patch 4/4] KVM: VMX: update vcpu posted-interrupt descriptor when assigning device
Date: Tue, 25 May 2021 13:58:50 +0200	[thread overview]
Message-ID: <40b253f3-7a90-bf7a-8480-b9fa6eb30526@redhat.com> (raw)
In-Reply-To: <20210524175329.GA19468@fuller.cnet>

On 24/05/21 19:53, Marcelo Tosatti wrote:
> On Mon, May 24, 2021 at 05:55:18PM +0200, Paolo Bonzini wrote:
>> On 10/05/21 19:26, Marcelo Tosatti wrote:
>>> +void vmx_pi_start_assignment(struct kvm *kvm)
>>> +{
>>> +	struct kvm_vcpu *vcpu;
>>> +	int i;
>>> +
>>> +	if (!irq_remapping_cap(IRQ_POSTING_CAP))
>>> +		return;
>>> +
>>> +	/*
>>> +	 * Wakeup will cause the vCPU to bail out of kvm_vcpu_block() and
>>> +	 * go back through vcpu_block().
>>> +	 */
>>> +	kvm_for_each_vcpu(i, vcpu, kvm) {
>>> +		if (!kvm_vcpu_apicv_active(vcpu))
>>> +			continue;
>>> +
>>> +		kvm_vcpu_wake_up(vcpu);
>>
>> Would you still need the check_block callback, if you also added a
>> kvm_make_request(KVM_REQ_EVENT)?
>>
>> In fact, since this is entirely not a hot path, can you just do
>> kvm_make_all_cpus_request(kvm, KVM_REQ_EVENT) instead of this loop?
>>
>> Thanks,
>>
>> Paolo
> 
> Hi Paolo,
> 
> Don't think so:
> 
> static int kvm_vcpu_check_block(struct kvm_vcpu *vcpu)
> {
>          int ret = -EINTR;
>          int idx = srcu_read_lock(&vcpu->kvm->srcu);
> 
>          if (kvm_arch_vcpu_runnable(vcpu)) {
>                  kvm_make_request(KVM_REQ_UNHALT, vcpu);  <---- don't want KVM_REQ_UNHALT

UNHALT is incorrect indeed, but requests don't have to unhalt the vCPU.

This case is somewhat similar to signal_pending(), where the next 
KVM_RUN ioctl resumes the halt.  It's also similar to 
KVM_REQ_PENDING_TIMER.  So you can:

- rename KVM_REQ_PENDING_TIMER to KVM_REQ_UNBLOCK except in 
arch/powerpc, where instead you add KVM_REQ_PENDING_TIMER to 
arch/powerpc/include/asm/kvm_host.h

- here, you add

	if (kvm_check_request(KVM_REQ_UNBLOCK, vcpu))
		goto out;

- then vmx_pi_start_assignment only needs to

	if (!irq_remapping_cap(IRQ_POSTING_CAP))
		return;
	kvm_make_all_cpus_request(kvm, KVM_REQ_UNBLOCK);

kvm_arch_vcpu_runnable() would still return false, so the mp_state would 
not change.

Paolo


  reply	other threads:[~2021-05-25 11:58 UTC|newest]

Thread overview: 26+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-05-10 17:26 [patch 0/4] VMX: configure posted interrupt descriptor when assigning device (v3) Marcelo Tosatti
2021-05-10 17:26 ` [patch 1/4] KVM: x86: add start_assignment hook to kvm_x86_ops Marcelo Tosatti
2021-05-11 16:26   ` Peter Xu
2021-05-11 17:29     ` Marcelo Tosatti
2021-05-10 17:26 ` [patch 2/4] KVM: add arch specific vcpu_check_block callback Marcelo Tosatti
2021-05-10 17:26 ` [patch 3/4] KVM: x86: implement kvm_arch_vcpu_check_block callback Marcelo Tosatti
2021-05-10 17:26 ` [patch 4/4] KVM: VMX: update vcpu posted-interrupt descriptor when assigning device Marcelo Tosatti
2021-05-24 15:55   ` Paolo Bonzini
2021-05-24 17:53     ` Marcelo Tosatti
2021-05-25 11:58       ` Paolo Bonzini [this message]
  -- strict thread matches above, loose matches on Subject: below --
2021-05-11 23:57 [patch 0/4] VMX: configure posted interrupt descriptor when assigning device (v4) Marcelo Tosatti
2021-05-11 23:57 ` [patch 4/4] KVM: VMX: update vcpu posted-interrupt descriptor when assigning device Marcelo Tosatti
2021-05-07 13:06 [patch 0/4] VMX: configure posted interrupt " Marcelo Tosatti
2021-05-07 13:06 ` [patch 4/4] KVM: VMX: update vcpu posted-interrupt " Marcelo Tosatti
2021-05-07 17:22   ` Sean Christopherson
2021-05-07 19:29     ` Peter Xu
2021-05-07 22:08       ` Marcelo Tosatti
2021-05-11 14:39         ` Peter Xu
2021-05-11 14:51           ` Marcelo Tosatti
2021-05-11 16:19             ` Peter Xu
2021-05-11 17:18               ` Marcelo Tosatti
2021-05-11 21:35                 ` Peter Xu
2021-05-11 23:51                   ` Marcelo Tosatti
2021-05-12  0:02                     ` Marcelo Tosatti
2021-05-12  0:38                       ` Peter Xu
2021-05-12 11:10                         ` Marcelo Tosatti
2021-05-12 14:41                       ` Sean Christopherson
2021-05-12 15:34                         ` Peter Xu

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