accel: introduce accelerator blocker API

This API allows the accelerators to prevent vcpus from issuing
new ioctls while execting a critical section marked with the
accel_ioctl_inhibit_begin/end functions.

Note that all functions submitting ioctls must mark where the
ioctl is being called with accel_{cpu_}ioctl_begin/end().

This API requires the caller to always hold the BQL.
API documentation is in sysemu/accel-blocker.h

Internally, it uses a QemuLockCnt together with a per-CPU QemuLockCnt
(to minimize cache line bouncing) to keep avoid that new ioctls
run when the critical section starts, and a QemuEvent to wait
that all running ioctls finish.

Signed-off-by: Emanuele Giuseppe Esposito <eesposit@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Message-Id: <20221111154758.1372674-2-eesposit@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

1 files changed, 3 insertions, 0 deletions

diff --git a/include/hw/core/cpu.h b/include/hw/core/cpu.h
index 8830546121..2417597236 100644
--- a/include/hw/core/cpu.h
+++ b/include/hw/core/cpu.h
@@ -398,6 +398,9 @@ struct CPUState {
     uint32_t kvm_fetch_index;
     uint64_t dirty_pages;
 
+    /* Use by accel-block: CPU is executing an ioctl() */
+    QemuLockCnt in_ioctl_lock;
+
     /* Used for events with 'vcpu' and *without* the 'disabled' properties */
     DECLARE_BITMAP(trace_dstate_delayed, CPU_TRACE_DSTATE_MAX_EVENTS);
     DECLARE_BITMAP(trace_dstate, CPU_TRACE_DSTATE_MAX_EVENTS);