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Code Issues Releases Wiki Activity

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

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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: Sean Christopherson <seanjc@google.com>
Message-Id: <20211208015236.1616697-22-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Sean Christopherson 2021-12-08 01:52:31 +00:00 committed by Paolo Bonzini
parent 635e6357f9
commit 935a733395
1 changed files with 36 additions and 20 deletions
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56
arch/x86/kvm/svm/avic.c
View file

@ -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)
{
int cpu = get_cpu();
WARN_ON(cpu != vcpu->cpu);
if (kvm_vcpu_apicv_active(vcpu)) {
if (is_run)
avic_vcpu_load(vcpu, cpu);
else
avic_vcpu_put(vcpu);
}
put_cpu();
}
void svm_vcpu_blocking(struct kvm_vcpu *vcpu)
{
avic_set_running(vcpu, false);
if (!kvm_vcpu_apicv_active(vcpu))
return;
preempt_disable();
/*
* 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);
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();
}