[PATCH v2 13/20] KVM: x86/xen: Don't bother waiting on gpc->lock in SCHEDOP_poll

[Sean Christopherson]

Use trylock instead of waiting on the gpc->lock when locking and checking
the shared info page for SCHEDOP_poll, as odds are very good that if the
lock is contended, then the check will fail.  This will allow using the new
CLASS() APIs for local gpc mappings, without having to add a version that
waits on the lock, but doesn't refresh on failure.

Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx>
---
 arch/x86/kvm/xen.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kvm/xen.c b/arch/x86/kvm/xen.c
index 065b4c92f7ed..d9b09809e243 100644
--- a/arch/x86/kvm/xen.c
+++ b/arch/x86/kvm/xen.c
@@ -1438,7 +1438,9 @@ static bool wait_pending_event(struct kvm_vcpu *vcpu, int nr_ports,
 
 	guard(srcu)(&kvm->srcu);
 
-	read_lock(&gpc->lock);
+	if (!read_trylock(&gpc->lock))
+		return ret;
+
 	if (!kvm_gpc_check(gpc, PAGE_SIZE))
 		goto out_rcu;
 
-- 
2.54.0.823.g6e5bcc1fc9-goog