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KVM: X86: correct meaningless kvm_apicv_activated() check

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After test_and_set_bit() for kvm->arch.apicv_inhibit_reasons, we will
always get false when calling kvm_apicv_activated() because it's sure
apicv_inhibit_reasons do not equal to 0.

What the code wants to do, is check whether APICv was *already* active
and if so skip the costly request; we can do this using cmpxchg.

Reported-by: Miaohe Lin <linmiaohe@huawei.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Paolo Bonzini 2020-03-14 12:29:23 +01:00
parent 212617dbb6
commit 8e205a6b2a
1 changed files with 16 additions and 9 deletions
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25
arch/x86/kvm/x86.c
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@ -8049,19 +8049,26 @@ EXPORT_SYMBOL_GPL(kvm_vcpu_update_apicv);
*/
void kvm_request_apicv_update(struct kvm *kvm, bool activate, ulong bit)
{
unsigned long old, new, expected;
if (!kvm_x86_ops->check_apicv_inhibit_reasons ||
!kvm_x86_ops->check_apicv_inhibit_reasons(bit))
return;
if (activate) {
if (!test_and_clear_bit(bit, &kvm->arch.apicv_inhibit_reasons) ||
!kvm_apicv_activated(kvm))
return;
} else {
if (test_and_set_bit(bit, &kvm->arch.apicv_inhibit_reasons) ||
kvm_apicv_activated(kvm))
return;
}
old = READ_ONCE(kvm->arch.apicv_inhibit_reasons);
do {
expected = new = old;
if (activate)
__clear_bit(bit, &new);
else
__set_bit(bit, &new);
if (new == old)
break;
old = cmpxchg(&kvm->arch.apicv_inhibit_reasons, expected, new);
} while (old != expected);
if (!!old == !!new)
return;
trace_kvm_apicv_update_request(activate, bit);
if (kvm_x86_ops->pre_update_apicv_exec_ctrl)