xen/arm32: Use alternative to skip the check of pending serrors

We have provided an option to administrator to determine how to
handle the SErrors. In order to skip the check of pending SError,
in conventional way, we have to read the option every time before
we try to check the pending SError. This will add overhead to check
the option at every trap.

The ARM32 supports the alternative patching feature. We can use an
ALTERNATIVE to avoid checking option at every trap. We added a new
cpufeature named "SKIP_SYNCHRONIZE_SERROR_ENTRY_EXIT". This feature
will be enabled when the option is not diverse.

Signed-off-by: Wei Chen <Wei.Chen@arm.com>
Reviewed-by: Julien Grall <julien.grall@arm.com>

diff --git a/xen/arch/arm/arm32/entry.S b/xen/arch/arm/arm32/entry.S
index 2187226b129be7803dfb92733c5742b5638471cb..8cd21238af5b26ef88cdad52acaedf10b456c9ef 100644 (file)
--- a/xen/arch/arm/arm32/entry.S
+++ b/xen/arch/arm/arm32/entry.S
@@ -1,5 +1,6 @@
 #include <asm/asm_defns.h>
 #include <asm/regs.h>
+#include <asm/alternative.h>
 #include <public/xen.h>
 
 #define SAVE_ONE_BANKED(reg)    mrs r11, reg; str r11, [sp, #UREGS_##reg]
@@ -44,6 +45,14 @@ save_guest_regs:
         SAVE_BANKED(fiq)
         SAVE_ONE_BANKED(R8_fiq); SAVE_ONE_BANKED(R9_fiq); SAVE_ONE_BANKED(R10_fiq)
         SAVE_ONE_BANKED(R11_fiq); SAVE_ONE_BANKED(R12_fiq);
+
+        /*
+         * If the SKIP_SYNCHRONIZE_SERROR_ENTRY_EXIT has been set in the cpu
+         * feature, the checking of pending SErrors will be skipped.
+         */
+        ALTERNATIVE("nop",
+                    "b skip_check",
+                    SKIP_SYNCHRONIZE_SERROR_ENTRY_EXIT)
         /*
          * Start to check pending virtual abort in the gap of Guest -> HYP
          * world switch.
@@ -99,6 +108,7 @@ abort_guest_exit_end:
          */
         bne return_from_trap
 
+skip_check:
         mov pc, lr
 
 #define DEFINE_TRAP_ENTRY(trap)                                         \