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| author | Paolo Bonzini <pbonzini@redhat.com> | 2017-02-08 13:50:15 +0300 |
|---|---|---|
| committer | Paolo Bonzini <pbonzini@redhat.com> | 2017-02-17 14:27:37 +0300 |
| commit | 460df4c1fc7c00829050c08d6368dc6e6beef307 (patch) | |
| tree | 72c996f591c82ce12e2bc544ae9c9cc6e2aed81e /include/uapi/linux/kvm.h | |
| parent | bbd6411513aa8ef3ea02abab61318daf87c1af1e (diff) | |
| download | linux-460df4c1fc7c00829050c08d6368dc6e6beef307.tar.xz | |
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 'include/uapi/linux/kvm.h')
| -rw-r--r-- | include/uapi/linux/kvm.h | 4 |
1 files changed, 3 insertions, 1 deletions
diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h index 7964b970b9ad..f51d5082a377 100644 --- a/include/uapi/linux/kvm.h +++ b/include/uapi/linux/kvm.h @@ -218,7 +218,8 @@ struct kvm_hyperv_exit { struct kvm_run { /* in */ __u8 request_interrupt_window; - __u8 padding1[7]; + __u8 immediate_exit; + __u8 padding1[6]; /* out */ __u32 exit_reason; @@ -881,6 +882,7 @@ struct kvm_ppc_resize_hpt { #define KVM_CAP_SPAPR_RESIZE_HPT 133 #define KVM_CAP_PPC_MMU_RADIX 134 #define KVM_CAP_PPC_MMU_HASH_V3 135 +#define KVM_CAP_IMMEDIATE_EXIT 136 #ifdef KVM_CAP_IRQ_ROUTING |