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| author | Paolo Bonzini <pbonzini@redhat.com> | 2020-03-14 12:29:23 +0100 |
|---|---|---|
| committer | Paolo Bonzini <pbonzini@redhat.com> | 2020-03-16 17:58:59 +0100 |
| commit | 8e205a6b2a06764a4c2bfc9e1a6a8a8e7920faf8 (patch) | |
| tree | f28323015730289c4f9d57a023bd404ab016cf30 /arch/x86/kvm | |
| parent | 212617dbb6bac2a21dec6ef7d6012d96bb6dbb5d (diff) | |
| download | linux-8e205a6b2a06764a4c2bfc9e1a6a8a8e7920faf8.tar.bz2 | |
KVM: X86: correct meaningless kvm_apicv_activated() check
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>
Diffstat (limited to 'arch/x86/kvm')
| -rw-r--r-- | arch/x86/kvm/x86.c | 25 |
1 files changed, 16 insertions, 9 deletions
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index a7cb85231330..e54c6ad628a8 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -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) |