arm64: mm: avoid x18 in idmap_kpti_install_ng_mappings

idmap_kpti_install_ng_mappings uses x18 as a temporary register, which
will result in a conflict when x18 is reserved. Use x16 and x17 instead
where needed.
Signed-off-by: Sami Tolvanen <samitolvanen@google.com>
Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
Reviewed-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Will Deacon <will@kernel.org>

arch/arm64/mm/proc.S

@@ -250,15 +250,15 @@ ENTRY(idmap_kpti_install_ng_mappings)
 	/* We're the boot CPU. Wait for the others to catch up */
 	sevl
 1:	wfe
-	ldaxr	w18, [flag_ptr]
-	eor	w18, w18, num_cpus
-	cbnz	w18, 1b
+	ldaxr	w17, [flag_ptr]
+	eor	w17, w17, num_cpus
+	cbnz	w17, 1b
 
 	/* We need to walk swapper, so turn off the MMU. */
 	pre_disable_mmu_workaround
-	mrs	x18, sctlr_el1
-	bic	x18, x18, #SCTLR_ELx_M
-	msr	sctlr_el1, x18
+	mrs	x17, sctlr_el1
+	bic	x17, x17, #SCTLR_ELx_M
+	msr	sctlr_el1, x17
 	isb
 
 	/* Everybody is enjoying the idmap, so we can rewrite swapper. */
@@ -281,9 +281,9 @@ skip_pgd:
 	isb
 
 	/* We're done: fire up the MMU again */
-	mrs	x18, sctlr_el1
-	orr	x18, x18, #SCTLR_ELx_M
-	msr	sctlr_el1, x18
+	mrs	x17, sctlr_el1
+	orr	x17, x17, #SCTLR_ELx_M
+	msr	sctlr_el1, x17
 	isb
 
 	/*
@@ -353,46 +353,47 @@ skip_pte:
 	b.ne	do_pte
 	b	next_pmd
 
+	.unreq	cpu
+	.unreq	num_cpus
+	.unreq	swapper_pa
+	.unreq	cur_pgdp
+	.unreq	end_pgdp
+	.unreq	pgd
+	.unreq	cur_pudp
+	.unreq	end_pudp
+	.unreq	pud
+	.unreq	cur_pmdp
+	.unreq	end_pmdp
+	.unreq	pmd
+	.unreq	cur_ptep
+	.unreq	end_ptep
+	.unreq	pte
+
 	/* Secondary CPUs end up here */
 __idmap_kpti_secondary:
 	/* Uninstall swapper before surgery begins */
-	__idmap_cpu_set_reserved_ttbr1 x18, x17
+	__idmap_cpu_set_reserved_ttbr1 x16, x17
 
 	/* Increment the flag to let the boot CPU we're ready */
-1:	ldxr	w18, [flag_ptr]
-	add	w18, w18, #1
-	stxr	w17, w18, [flag_ptr]
+1:	ldxr	w16, [flag_ptr]
+	add	w16, w16, #1
+	stxr	w17, w16, [flag_ptr]
 	cbnz	w17, 1b
 
 	/* Wait for the boot CPU to finish messing around with swapper */
 	sevl
 1:	wfe
-	ldxr	w18, [flag_ptr]
-	cbnz	w18, 1b
+	ldxr	w16, [flag_ptr]
+	cbnz	w16, 1b
 
 	/* All done, act like nothing happened */
-	offset_ttbr1 swapper_ttb, x18
+	offset_ttbr1 swapper_ttb, x16
 	msr	ttbr1_el1, swapper_ttb
 	isb
 	ret
 
-	.unreq	cpu
-	.unreq	num_cpus
-	.unreq	swapper_pa
 	.unreq	swapper_ttb
 	.unreq	flag_ptr
-	.unreq	cur_pgdp
-	.unreq	end_pgdp
-	.unreq	pgd
-	.unreq	cur_pudp
-	.unreq	end_pudp
-	.unreq	pud
-	.unreq	cur_pmdp
-	.unreq	end_pmdp
-	.unreq	pmd
-	.unreq	cur_ptep
-	.unreq	end_ptep
-	.unreq	pte
 ENDPROC(idmap_kpti_install_ng_mappings)
 	.popsection
 #endif