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authorSean Christopherson <seanjc@google.com>2021-01-22 16:03:34 -0800
committerPaolo Bonzini <pbonzini@redhat.com>2021-02-04 05:27:14 -0500
commit15b51dc08a349f2f0832606c900b638a3dd19839 (patch)
tree2333c9a496b81bcfd5247b425a313eea321e3a63
parent19979fba9bfaeab427a8e106d915f0627c952828 (diff)
KVM: x86: Take KVM's SRCU lock only if steal time update is needed
Enter a SRCU critical section for a memslots lookup during steal time update if and only if a steal time update is actually needed. Taking the lock can be avoided if steal time is disabled by the guest, or if KVM knows it has already flagged the vCPU as being preempted. Reword the comment to be more precise as to exactly why memslots will be queried. Signed-off-by: Sean Christopherson <seanjc@google.com> Message-Id: <20210123000334.3123628-3-seanjc@google.com> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
-rw-r--r--arch/x86/kvm/x86.c20
1 files changed, 11 insertions, 9 deletions
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 18d005378a78..fa1ec597d510 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -4014,6 +4014,7 @@ static void kvm_steal_time_set_preempted(struct kvm_vcpu *vcpu)
{
struct kvm_host_map map;
struct kvm_steal_time *st;
+ int idx;
if (!(vcpu->arch.st.msr_val & KVM_MSR_ENABLED))
return;
@@ -4021,9 +4022,15 @@ static void kvm_steal_time_set_preempted(struct kvm_vcpu *vcpu)
if (vcpu->arch.st.preempted)
return;
+ /*
+ * Take the srcu lock as memslots will be accessed to check the gfn
+ * cache generation against the memslots generation.
+ */
+ idx = srcu_read_lock(&vcpu->kvm->srcu);
+
if (kvm_map_gfn(vcpu, vcpu->arch.st.msr_val >> PAGE_SHIFT, &map,
&vcpu->arch.st.cache, true))
- return;
+ goto out;
st = map.hva +
offset_in_page(vcpu->arch.st.msr_val & KVM_STEAL_VALID_BITS);
@@ -4031,22 +4038,17 @@ static void kvm_steal_time_set_preempted(struct kvm_vcpu *vcpu)
st->preempted = vcpu->arch.st.preempted = KVM_VCPU_PREEMPTED;
kvm_unmap_gfn(vcpu, &map, &vcpu->arch.st.cache, true, true);
+
+out:
+ srcu_read_unlock(&vcpu->kvm->srcu, idx);
}
void kvm_arch_vcpu_put(struct kvm_vcpu *vcpu)
{
- int idx;
-
if (vcpu->preempted && !vcpu->arch.guest_state_protected)
vcpu->arch.preempted_in_kernel = !kvm_x86_ops.get_cpl(vcpu);
- /*
- * kvm_memslots() will be called by
- * kvm_write_guest_offset_cached() so take the srcu lock.
- */
- idx = srcu_read_lock(&vcpu->kvm->srcu);
kvm_steal_time_set_preempted(vcpu);
- srcu_read_unlock(&vcpu->kvm->srcu, idx);
kvm_x86_ops.vcpu_put(vcpu);
vcpu->arch.last_host_tsc = rdtsc();
/*