[Xen-changelog] [xen-unstable] arm: avoid memory write in switch to Hyp mode

[Xen patchbot-unstable <patchbot@xxxxxxx>]

# HG changeset patch
# User Tim Deegan <tim@xxxxxxx>
# Date 1338542438 -3600
# Node ID b2d9f2411d711d8177acf1af0fbe9f0c9115c7ef
# Parent  b2649ecbe06f5624ca42066ea9d506eed1562d55
arm: avoid memory write in switch to Hyp mode

Assemble the new CPSR in registers instead.  It's slightly cleaner,
And makes it possible to have a read-only text section.

Signed-off-by: Tim Deegan <tim@xxxxxxx>
Acked-by: Ian Campbell <ian.campbell@xxxxxxxxxx>
Committed-by: Ian Campbell <ian.campbell@xxxxxxxxxx>
---


diff -r b2649ecbe06f -r b2d9f2411d71 xen/arch/arm/mode_switch.S
--- a/xen/arch/arm/mode_switch.S        Fri Jun 01 10:20:37 2012 +0100
+++ b/xen/arch/arm/mode_switch.S        Fri Jun 01 10:20:38 2012 +0100
@@ -66,11 +66,7 @@ enter_hyp_mode:
        mcr   CP32(r0, FCSEIDR)
        mcr   CP32(r0, CONTEXTIDR)
        /* FIXME: ought to reset some other NS control regs here */
-       adr   r1, 1f                 /* Store return address */
-       str   r3, [r1]               /* where we can use it for RFE */
-       isb                          /* Ensure we see the stored address */
-       rfeia r1                     /* Enter Hyp mode */
-
-1:     .word 0                      /* PC to enter Hyp mode at */
-       .word 0x000001da             /* CPSR: LE, Abort/IRQ/FIQ off, Hyp */
-
+       mrs   r0, cpsr               /* Copy the CPSR */
+       add   r0, r0, #0x4           /* 0x16 (Monitor) -> 0x1a (Hyp) */
+       msr   spsr_cxsf, r0          /* into the SPSR */
+       movs  pc, r3                 /* Exception-return into Hyp mode */

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