[PATCH] xen/arm: fix unmapped access trapping on GICv2 hardware

[Stewart Hildebrand <stewart.hildebrand@xxxxxxx>]

Since 4dbcb0653621, the vGICv2 CPU interface is mapped in a deferred
manner. On domains with XEN_DOMCTL_CDF_trap_unmapped_accesses unset on
GICv2 hardware, the vGICv2 CPU interface fails to be mapped. A visible
symptom is that a domU gets stuck at:

  [    0.177983] smp: Bringing up secondary CPUs ...

Move the 2nd check_p2m earlier so it's prioritized over try_handle_mmio.

Fixes: 980aff4e8fcd ("xen/arm: Add way to disable traps on accesses to unmapped 
addresses")
Signed-off-by: Stewart Hildebrand <stewart.hildebrand@xxxxxxx>
---
This should be backported to 4.21.

Pipeline: 
https://gitlab.com/xen-project/people/stewarthildebrand/xen/-/pipelines/2010469665
---
 xen/arch/arm/traps.c | 16 ++++++++--------
 1 file changed, 8 insertions(+), 8 deletions(-)

diff --git a/xen/arch/arm/traps.c b/xen/arch/arm/traps.c
index 040c0f2e0db1..0c01f37ad6b4 100644
--- a/xen/arch/arm/traps.c
+++ b/xen/arch/arm/traps.c
@@ -1915,6 +1915,14 @@ static void do_trap_stage2_abort_guest(struct 
cpu_user_regs *regs,
         if ( info.dabt_instr.state == INSTR_ERROR )
             goto inject_abt;
 
+        /*
+         * If the instruction syndrome was invalid, then we already checked if
+         * this was due to a P2M fault. So no point to check again as the 
result
+         * will be the same.
+         */
+        if ( (info.dabt_instr.state == INSTR_VALID) && check_p2m(is_data, gpa) 
)
+            return;
+
         state = try_handle_mmio(regs, &info);
 
         switch ( state )
@@ -1939,14 +1947,6 @@ static void do_trap_stage2_abort_guest(struct 
cpu_user_regs *regs,
                 break;
         }
 
-        /*
-         * If the instruction syndrome was invalid, then we already checked if
-         * this was due to a P2M fault. So no point to check again as the 
result
-         * will be the same.
-         */
-        if ( (info.dabt_instr.state == INSTR_VALID) && check_p2m(is_data, gpa) 
)
-            return;
-
         break;
     }
     default:
-- 
2.52.0