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SubjectRe: [PATCH 1/2] KVM: x86: reduce pvclock_gtod_sync_lock critical sections
On Wed, 31 Mar 2021 at 01:02, Paolo Bonzini <pbonzini@redhat.com> wrote:
>
> There is no need to include changes to vcpu->requests into
> the pvclock_gtod_sync_lock critical section. The changes to
> the shared data structures (in pvclock_update_vm_gtod_copy)
> already occur under the lock.
>
> Cc: David Woodhouse <dwmw@amazon.co.uk>
> Cc: Marcelo Tosatti <mtosatti@redhat.com>
> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

Reviewed-by: Wanpeng Li <wanpengli@tencent.com>

> ---
> arch/x86/kvm/x86.c | 10 ++++------
> 1 file changed, 4 insertions(+), 6 deletions(-)
>
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index fe806e894212..0a83eff40b43 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -2562,10 +2562,12 @@ static void kvm_gen_update_masterclock(struct kvm *kvm)
>
> kvm_hv_invalidate_tsc_page(kvm);
>
> - spin_lock(&ka->pvclock_gtod_sync_lock);
> kvm_make_mclock_inprogress_request(kvm);
> +
> /* no guest entries from this point */
> + spin_lock(&ka->pvclock_gtod_sync_lock);
> pvclock_update_vm_gtod_copy(kvm);
> + spin_unlock(&ka->pvclock_gtod_sync_lock);
>
> kvm_for_each_vcpu(i, vcpu, kvm)
> kvm_make_request(KVM_REQ_CLOCK_UPDATE, vcpu);
> @@ -2573,8 +2575,6 @@ static void kvm_gen_update_masterclock(struct kvm *kvm)
> /* guest entries allowed */
> kvm_for_each_vcpu(i, vcpu, kvm)
> kvm_clear_request(KVM_REQ_MCLOCK_INPROGRESS, vcpu);
> -
> - spin_unlock(&ka->pvclock_gtod_sync_lock);
> #endif
> }
>
> @@ -7740,16 +7740,14 @@ static void kvm_hyperv_tsc_notifier(void)
> struct kvm_arch *ka = &kvm->arch;
>
> spin_lock(&ka->pvclock_gtod_sync_lock);
> -
> pvclock_update_vm_gtod_copy(kvm);
> + spin_unlock(&ka->pvclock_gtod_sync_lock);
>
> kvm_for_each_vcpu(cpu, vcpu, kvm)
> kvm_make_request(KVM_REQ_CLOCK_UPDATE, vcpu);
>
> kvm_for_each_vcpu(cpu, vcpu, kvm)
> kvm_clear_request(KVM_REQ_MCLOCK_INPROGRESS, vcpu);
> -
> - spin_unlock(&ka->pvclock_gtod_sync_lock);
> }
> mutex_unlock(&kvm_lock);
> }
> --
> 2.26.2
>
>

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