Commit 935a7333 authored by Sean Christopherson's avatar Sean Christopherson Committed by Paolo Bonzini
Browse files

KVM: SVM: Drop AVIC's intermediate avic_set_running() helper 



Drop avic_set_running() in favor of calling avic_vcpu_{load,put}()
directly, and modify the block+put path to use preempt_disable/enable()
instead of get/put_cpu(), as it doesn't actually care about the current
pCPU associated with the vCPU.  Opportunistically add lockdep assertions
as being preempted in avic_vcpu_put() would lead to consuming stale data,
even though doing so _in the current code base_ would not be fatal.

Add a much needed comment explaining why svm_vcpu_blocking() needs to
unload the AVIC and update the IRTE _before_ the vCPU starts blocking.

Signed-off-by: default avatarSean Christopherson <seanjc@google.com>
Message-Id: <20211208015236.1616697-22-seanjc@google.com>
Signed-off-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
parent 635e6357

arch/x86/kvm/svm/avic.c

+36 −20
Original line number Diff line number Diff line
@@ -978,6 +978,8 @@ void avic_vcpu_load(struct kvm_vcpu *vcpu, int cpu) 
	int h_physical_id = kvm_cpu_get_apicid(cpu);

	struct vcpu_svm *svm = to_svm(vcpu);



	lockdep_assert_preemption_disabled();



	/*

	 * Since the host physical APIC id is 8 bits,

	 * we can support host APIC ID upto 255.
@@ -1011,6 +1013,8 @@ void avic_vcpu_put(struct kvm_vcpu *vcpu) 
	u64 entry;

	struct vcpu_svm *svm = to_svm(vcpu);



	lockdep_assert_preemption_disabled();



	entry = READ_ONCE(*(svm->avic_physical_id_cache));



	/* Nothing to do if IsRunning == '0' due to vCPU blocking. */
@@ -1023,30 +1027,42 @@ void avic_vcpu_put(struct kvm_vcpu *vcpu) 
	WRITE_ONCE(*(svm->avic_physical_id_cache), entry);

}



/*

 * This function is called during VCPU halt/unhalt.

 */

static void avic_set_running(struct kvm_vcpu *vcpu, bool is_run)

void svm_vcpu_blocking(struct kvm_vcpu *vcpu)

{

	int cpu = get_cpu();

	if (!kvm_vcpu_apicv_active(vcpu))

		return;



	WARN_ON(cpu != vcpu->cpu);

	preempt_disable();



	if (kvm_vcpu_apicv_active(vcpu)) {

		if (is_run)

			avic_vcpu_load(vcpu, cpu);

		else

       /*

        * Unload the AVIC when the vCPU is about to block, _before_

        * the vCPU actually blocks.

        *

        * Any IRQs that arrive before IsRunning=0 will not cause an

        * incomplete IPI vmexit on the source, therefore vIRR will also

        * be checked by kvm_vcpu_check_block() before blocking.  The

        * memory barrier implicit in set_current_state orders writing

        * IsRunning=0 before reading the vIRR.  The processor needs a

        * matching memory barrier on interrupt delivery between writing

        * IRR and reading IsRunning; the lack of this barrier might be

        * the cause of errata #1235).

        */

	avic_vcpu_put(vcpu);

	}

	put_cpu();

}



void svm_vcpu_blocking(struct kvm_vcpu *vcpu)

{

	avic_set_running(vcpu, false);

	preempt_enable();

}



void svm_vcpu_unblocking(struct kvm_vcpu *vcpu)

{

	avic_set_running(vcpu, true);

	int cpu;



	if (!kvm_vcpu_apicv_active(vcpu))

		return;



	cpu = get_cpu();

	WARN_ON(cpu != vcpu->cpu);



	avic_vcpu_load(vcpu, cpu);



	put_cpu();

}