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authorPaolo Bonzini <pbonzini@redhat.com>2017-02-08 11:50:15 +0100
committerPaolo Bonzini <pbonzini@redhat.com>2017-02-17 12:27:37 +0100
commit460df4c1fc7c00829050c08d6368dc6e6beef307 (patch)
tree72c996f591c82ce12e2bc544ae9c9cc6e2aed81e /arch/mips/kvm
parentbbd6411513aa8ef3ea02abab61318daf87c1af1e (diff)
downloadlinux-460df4c1fc7c00829050c08d6368dc6e6beef307.tar.bz2
KVM: race-free exit from KVM_RUN without POSIX signals
The purpose of the KVM_SET_SIGNAL_MASK API is to let userspace "kick" a VCPU out of KVM_RUN through a POSIX signal. A signal is attached to a dummy signal handler; by blocking the signal outside KVM_RUN and unblocking it inside, this possible race is closed: VCPU thread service thread -------------------------------------------------------------- check flag set flag raise signal (signal handler does nothing) KVM_RUN However, one issue with KVM_SET_SIGNAL_MASK is that it has to take tsk->sighand->siglock on every KVM_RUN. This lock is often on a remote NUMA node, because it is on the node of a thread's creator. Taking this lock can be very expensive if there are many userspace exits (as is the case for SMP Windows VMs without Hyper-V reference time counter). As an alternative, we can put the flag directly in kvm_run so that KVM can see it: VCPU thread service thread -------------------------------------------------------------- raise signal signal handler set run->immediate_exit KVM_RUN check run->immediate_exit Reviewed-by: Radim Krčmář <rkrcmar@redhat.com> Reviewed-by: David Hildenbrand <david@redhat.com> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Diffstat (limited to 'arch/mips/kvm')
-rw-r--r--arch/mips/kvm/mips.c7
1 files changed, 6 insertions, 1 deletions
diff --git a/arch/mips/kvm/mips.c b/arch/mips/kvm/mips.c
index 31ee5ee0010b..ed81e5ac1426 100644
--- a/arch/mips/kvm/mips.c
+++ b/arch/mips/kvm/mips.c
@@ -397,7 +397,7 @@ int kvm_arch_vcpu_ioctl_set_guest_debug(struct kvm_vcpu *vcpu,
int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu, struct kvm_run *run)
{
- int r = 0;
+ int r = -EINTR;
sigset_t sigsaved;
if (vcpu->sigset_active)
@@ -409,6 +409,9 @@ int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu, struct kvm_run *run)
vcpu->mmio_needed = 0;
}
+ if (run->immediate_exit)
+ goto out;
+
lose_fpu(1);
local_irq_disable();
@@ -429,6 +432,7 @@ int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu, struct kvm_run *run)
guest_exit_irqoff();
local_irq_enable();
+out:
if (vcpu->sigset_active)
sigprocmask(SIG_SETMASK, &sigsaved, NULL);
@@ -1021,6 +1025,7 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
case KVM_CAP_ENABLE_CAP:
case KVM_CAP_READONLY_MEM:
case KVM_CAP_SYNC_MMU:
+ case KVM_CAP_IMMEDIATE_EXIT:
r = 1;
break;
case KVM_CAP_COALESCED_MMIO: