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    Subject[PATCH 1/6] xen/events: fix unmask_evtchn for PV on HVM guests
    Date
    When unmask_evtchn is called, if we already have an event pending, we
    just set evtchn_pending_sel waiting for local_irq_enable to be called.
    That is because PV guests set the irq_enable pvops to
    xen_irq_enable_direct in xen_setup_vcpu_info_placement:
    xen_irq_enable_direct is implemented in assembly in
    arch/x86/xen/xen-asm.S and call xen_force_evtchn_callback if
    XEN_vcpu_info_pending is set.

    However HVM guests (and ARM guests) do not change or do not have the
    irq_enable pvop, so evtchn_unmask cannot work properly for them.

    Considering that having the pending_irq bit set when unmask_evtchn is
    called is not very common, and it is simpler to keep the
    native_irq_enable implementation for HVM guests (and ARM guests), the
    best thing to do is just use the EVTCHNOP_unmask hypercall (Xen
    re-injects pending events in response).

    Signed-off-by: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
    ---
    drivers/xen/events.c | 17 ++++++++++++++---
    1 files changed, 14 insertions(+), 3 deletions(-)

    diff --git a/drivers/xen/events.c b/drivers/xen/events.c
    index 7595581..36bf17d 100644
    --- a/drivers/xen/events.c
    +++ b/drivers/xen/events.c
    @@ -373,11 +373,22 @@ static void unmask_evtchn(int port)
    {
    struct shared_info *s = HYPERVISOR_shared_info;
    unsigned int cpu = get_cpu();
    + int do_hypercall = 0, evtchn_pending = 0;

    BUG_ON(!irqs_disabled());

    - /* Slow path (hypercall) if this is a non-local port. */
    - if (unlikely(cpu != cpu_from_evtchn(port))) {
    + if (unlikely((cpu != cpu_from_evtchn(port))))
    + do_hypercall = 1;
    + else
    + evtchn_pending = sync_test_bit(port, &s->evtchn_pending[0]);
    +
    + if (unlikely(evtchn_pending && xen_hvm_domain()))
    + do_hypercall = 1;
    +
    + /* Slow path (hypercall) if this is a non-local port or if this is
    + * an hvm domain and an event is pending (hvm domains don't have
    + * their own implementation of irq_enable). */
    + if (do_hypercall) {
    struct evtchn_unmask unmask = { .port = port };
    (void)HYPERVISOR_event_channel_op(EVTCHNOP_unmask, &unmask);
    } else {
    @@ -390,7 +401,7 @@ static void unmask_evtchn(int port)
    * 'hw_resend_irq'. Just like a real IO-APIC we 'lose
    * the interrupt edge' if the channel is masked.
    */
    - if (sync_test_bit(port, &s->evtchn_pending[0]) &&
    + if (evtchn_pending &&
    !sync_test_and_set_bit(port / BITS_PER_LONG,
    &vcpu_info->evtchn_pending_sel))
    vcpu_info->evtchn_upcall_pending = 1;
    --
    1.7.2.5


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