arm: lr register in hyp mode is really LR_usr.

Save and restore it in the same way for both hypervisor and user stack frames
rather than saving both individually in the user stack frame.

Signed-off-by: Ian Campbell <ian.campbell@citrix.com>
Acked-by: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
Committed-by: Ian Campbell <Ian.Campbell@citrix.com>

xen/arch/arm/entry.S

@@ -29,11 +29,10 @@
 	blne save_guest_regs
 
 save_guest_regs:
-	ldr r11, [sp, #UREGS_lr]
-	str r11, [sp, #UREGS_LR_usr]
 	ldr r11, =0xffffffff  /* Clobber SP which is only valid for hypervisor frames. */
 	str r11, [sp, #UREGS_sp]
 	SAVE_ONE_BANKED(SP_usr)
+	/* LR_usr is the same physical register as lr and is saved in SAVE_ALL */
 	SAVE_BANKED(svc)
 	SAVE_BANKED(abt)
 	SAVE_BANKED(und)
@@ -78,16 +77,13 @@ ENTRY(return_from_trap)
 	and r11, #PSR_MODE_MASK
 	cmp r11, #PSR_MODE_HYP
 	beq return_to_hypervisor
-
+	/* Fall thru */
 ENTRY(return_to_guest)
 	mov r11, sp
 	bic sp, #7 /* Align the stack pointer */
 	bl leave_hypervisor_tail
-	ldr r11, [sp, #UREGS_pc]
-	msr ELR_hyp, r11
-	ldr r11, [sp, #UREGS_cpsr]
-	msr SPSR_hyp, r11
 	RESTORE_ONE_BANKED(SP_usr)
+	/* LR_usr is the same physical register as lr and is restored below */
 	RESTORE_BANKED(svc)
 	RESTORE_BANKED(abt)
 	RESTORE_BANKED(und)
@@ -95,11 +91,7 @@ ENTRY(return_to_guest)
 	RESTORE_BANKED(fiq)
 	RESTORE_ONE_BANKED(R8_fiq); RESTORE_ONE_BANKED(R9_fiq); RESTORE_ONE_BANKED(R10_fiq)
 	RESTORE_ONE_BANKED(R11_fiq); RESTORE_ONE_BANKED(R12_fiq);
-	ldr lr, [sp, #UREGS_LR_usr]
-	pop {r0-r12}
-	add sp, #(UREGS_R8_fiq - UREGS_sp); /* SP, LR, SPSR, PC */
-	eret
-
+	/* Fall thru */
 ENTRY(return_to_hypervisor)
 	ldr lr, [sp, #UREGS_lr]
 	ldr r11, [sp, #UREGS_pc]

xen/include/public/arch-arm.h

@@ -63,7 +63,12 @@ struct cpu_user_regs
     uint32_t r12;
 
     uint32_t sp; /* r13 - SP: Valid for Hyp. frames only, o/w banked (see below) */
-    uint32_t lr; /* r14 - LR: Valid for Hyp. Same physical register as lr_usr. */
+
+    /* r14 - LR: is the same physical register as LR_usr */
+    union {
+        uint32_t lr; /* r14 - LR: Valid for Hyp. Same physical register as lr_usr. */
+        uint32_t lr_usr;
+    };
 
     uint32_t pc; /* Return IP */
     uint32_t cpsr; /* Return mode */
@@ -73,10 +78,14 @@ struct cpu_user_regs
 
     uint32_t r8_fiq, r9_fiq, r10_fiq, r11_fiq, r12_fiq;
 
-    uint32_t sp_usr, sp_svc, sp_abt, sp_und, sp_irq, sp_fiq;
-    uint32_t lr_usr, lr_svc, lr_abt, lr_und, lr_irq, lr_fiq;
+    uint32_t sp_usr; /* LR_usr is the same register as LR, see above */
+
+    uint32_t sp_svc, sp_abt, sp_und, sp_irq, sp_fiq;
+    uint32_t lr_svc, lr_abt, lr_und, lr_irq, lr_fiq;
 
     uint32_t spsr_svc, spsr_abt, spsr_und, spsr_irq, spsr_fiq;
+
+    uint32_t pad1; /* Doubleword-align the user half of the frame */
 };
 typedef struct cpu_user_regs cpu_user_regs_t;
 DEFINE_XEN_GUEST_HANDLE(cpu_user_regs_t);