File 5edf6ad8-ioreq-pending-emulation-server-destruction-race.patch of Package xen.15648

# Commit f7039ee41b3d3448775a1623f230037fd0455104
# Date 2020-06-09 12:56:24 +0200
# Author Paul Durrant <pdurrant@amazon.com>
# Committer Jan Beulich <jbeulich@suse.com>
ioreq: handle pending emulation racing with ioreq server destruction

When an emulation request is initiated in hvm_send_ioreq() the guest vcpu is
blocked on an event channel until that request is completed. If, however,
the emulator is killed whilst that emulation is pending then the ioreq
server may be destroyed. Thus when the vcpu is awoken the code in
handle_hvm_io_completion() will find no pending request to wait for, but will
leave the internal vcpu io_req.state set to IOREQ_READY and the vcpu shutdown
deferall flag in place (because hvm_io_assist() will never be called). The
emulation request is then completed anyway. This means that any subsequent call
to hvmemul_do_io() will find an unexpected value in io_req.state and will
return X86EMUL_UNHANDLEABLE, which in some cases will result in continuous
re-tries.

This patch fixes the issue by moving the setting of io_req.state and clearing
of shutdown deferral (as will as MSI-X write completion) out of hvm_io_assist()
and directly into handle_hvm_io_completion().

Reported-by: Marek Marczykowski-Górecki <marmarek@invisiblethingslab.com>
Signed-off-by: Paul Durrant <pdurrant@amazon.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>

--- a/xen/arch/x86/hvm/ioreq.c
+++ b/xen/arch/x86/hvm/ioreq.c
@@ -107,15 +107,7 @@ static void hvm_io_assist(struct hvm_ior
     ioreq_t *ioreq = &v->arch.hvm.hvm_io.io_req;
 
     if ( hvm_ioreq_needs_completion(ioreq) )
-    {
-        ioreq->state = STATE_IORESP_READY;
         ioreq->data = data;
-    }
-    else
-        ioreq->state = STATE_IOREQ_NONE;
-
-    msix_write_completion(v);
-    vcpu_end_shutdown_deferral(v);
 
     sv->pending = false;
 }
@@ -207,6 +199,12 @@ bool handle_hvm_io_completion(struct vcp
         }
     }
 
+    vio->io_req.state = hvm_ioreq_needs_completion(&vio->io_req) ?
+        STATE_IORESP_READY : STATE_IOREQ_NONE;
+
+    msix_write_completion(v);
+    vcpu_end_shutdown_deferral(v);
+
     io_completion = vio->io_completion;
     vio->io_completion = HVMIO_no_completion;