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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>
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|---|---|---|
| .. | ||
| hyp | ||
| arm.c | ||
| coproc_a7.c | ||
| coproc_a15.c | ||
| coproc.c | ||
| coproc.h | ||
| emulate.c | ||
| guest.c | ||
| handle_exit.c | ||
| init.S | ||
| interrupts.S | ||
| irq.h | ||
| Kconfig | ||
| Makefile | ||
| mmio.c | ||
| mmu.c | ||
| perf.c | ||
| psci.c | ||
| reset.c | ||
| trace.h | ||
| vgic-v3-coproc.c | ||