xen/arm32: head: Introduce an helper to flush the TLBs

The sequence for flushing the TLBs is 4 instruction long and often
requires an explanation how it works.

So create a helper and use it in the boot code (switch_ttbr() is left
alone until we decide the semantic of the call).

Note that in secondary_switched, we were also flushing the instruction
cache and branch predictor. Neither of them was necessary because:
    * We are only supporting IVIPT cache on arm32, so the instruction
      cache flush is only necessary when executable code is modified.
      None of the boot code is doing that.
    * The instruction cache is not invalidated and misprediction is not
      a problem at boot.

Signed-off-by: Julien Grall <jgrall@amazon.com>
Reviewed-by: Michal Orzel <michal.orzel@amd.com>
Reviewed-by: Henry Wang <Henry.Wang@arm.com>
Tested-by: Henry Wang <Henry.Wang@arm.com>

xen/arch/arm/arm32/head.S

@@ -66,6 +66,20 @@
         add   \rb, \rb, r10
 .endm
 
+/*
+ * Flush local TLBs
+ *
+ * @tmp: Scratch register
+ *
+ * See asm/arm32/flushtlb.h for the explanation of the sequence.
+ */
+.macro flush_xen_tlb_local tmp
+        dsb   nshst
+        mcr   CP32(\tmp, TLBIALLH)
+        dsb   nsh
+        isb
+.endm
+
 /*
  * Common register usage in this file:
  *   r0  -
@@ -232,11 +246,7 @@ secondary_switched:
         mcrr  CP64(r4, r5, HTTBR)
         dsb
         isb
-        mcr   CP32(r0, TLBIALLH)     /* Flush hypervisor TLB */
-        mcr   CP32(r0, ICIALLU)      /* Flush I-cache */
-        mcr   CP32(r0, BPIALL)       /* Flush branch predictor */
-        dsb                          /* Ensure completion of TLB+BP flush */
-        isb
+        flush_xen_tlb_local r0
 
 #ifdef CONFIG_EARLY_PRINTK
         /* Use a virtual address to access the UART. */
@@ -529,8 +539,7 @@ enable_mmu:
          * The state of the TLBs is unknown before turning on the MMU.
          * Flush them to avoid stale one.
          */
-        mcr   CP32(r0, TLBIALLH)     /* Flush hypervisor TLBs */
-        dsb   nsh
+        flush_xen_tlb_local r0
 
         /* Write Xen's PT's paddr into the HTTBR */
         load_paddr r0, boot_pgtable
@@ -605,12 +614,7 @@ remove_identity_mapping:
         strd  r2, r3, [r0, r1]
 
 identity_mapping_removed:
-        /* See asm/arm32/flushtlb.h for the explanation of the sequence. */
-        dsb   nshst
-        mcr   CP32(r0, TLBIALLH)
-        dsb   nsh
-        isb
-
+        flush_xen_tlb_local r0
         mov   pc, lr
 ENDPROC(remove_identity_mapping)