arm64: assembler: add conditional cache fixups

It would be helpful if we could use both `dcache_by_line_op` and
`invalidate_icache_by_line` for user memory without accidentally fixing
up unexpected faults when performing maintenance on kernel addresses.

Let's make this possible by having both macros take an optional fixup
label, and only generating an extable entry if a label is provided.

At the same time, let's clean up the labels used to be globally unique
using \@ as we do for other macros.

There should be no functional change as a result of this patch.
Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Fuad Tabba <tabba@google.com>
Cc: Ard Biesheuvel <aedb@kernel.org>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Fuad Tabba <tabba@google.com>
Cc: Will Deacon <will@kernel.org>
Reviewed-by: Ard Biesheuvel <ardb@kernel.org>
Link: https://lore.kernel.org/r/20210524083001.2586635-3-tabba@google.comSigned-off-by: Will Deacon <will@kernel.org>

arch/arm64/include/asm/assembler.h

@@ -130,15 +130,27 @@ alternative_endif
 	.endm
 
 /*
- * Emit an entry into the exception table
+ * Create an exception table entry for `insn`, which will branch to `fixup`
+ * when an unhandled fault is taken.
  */
-	.macro		_asm_extable, from, to
+	.macro		_asm_extable, insn, fixup
 	.pushsection	__ex_table, "a"
 	.align		3
-	.long		(\from - .), (\to - .)
+	.long		(\insn - .), (\fixup - .)
 	.popsection
 	.endm
 
+/*
+ * Create an exception table entry for `insn` if `fixup` is provided. Otherwise
+ * do nothing.
+ */
+	.macro		_cond_extable, insn, fixup
+	.ifnc		\fixup,
+	_asm_extable	\insn, \fixup
+	.endif
+	.endm
+
+
 #define USER(l, x...)				\
 9999:	x;					\
 	_asm_extable	9999b, l
@@ -383,6 +395,7 @@ alternative_cb_end
  * 	domain:		domain used in dsb instruciton
  * 	addr:		starting virtual address of the region
  * 	size:		size of the region
+ * 	fixup:		optional label to branch to on user fault
  * 	Corrupts:	addr, size, tmp1, tmp2
  */
 	.macro __dcache_op_workaround_clean_cache, op, addr
@@ -393,12 +406,12 @@ alternative_else
 alternative_endif
 	.endm
 
-	.macro dcache_by_line_op op, domain, addr, size, tmp1, tmp2
+	.macro dcache_by_line_op op, domain, addr, size, tmp1, tmp2, fixup
 	dcache_line_size \tmp1, \tmp2
 	add	\size, \addr, \size
 	sub	\tmp2, \tmp1, #1
 	bic	\addr, \addr, \tmp2
-9998:
+.Ldcache_op\@:
 	.ifc	\op, cvau
 	__dcache_op_workaround_clean_cache \op, \addr
 	.else
@@ -418,8 +431,10 @@ alternative_endif
 	.endif
 	add	\addr, \addr, \tmp1
 	cmp	\addr, \size
-	b.lo	9998b
+	b.lo	.Ldcache_op\@
 	dsb	\domain
+
+	_cond_extable .Ldcache_op\@, \fixup
 	.endm
 
 /*
@@ -427,20 +442,22 @@ alternative_endif
  * [start, end)
  *
  * 	start, end:	virtual addresses describing the region
- *	label:		A label to branch to on user fault.
+ *	fixup:		optional label to branch to on user fault
  * 	Corrupts:	tmp1, tmp2
  */
-	.macro invalidate_icache_by_line start, end, tmp1, tmp2, label
+	.macro invalidate_icache_by_line start, end, tmp1, tmp2, fixup
 	icache_line_size \tmp1, \tmp2
 	sub	\tmp2, \tmp1, #1
 	bic	\tmp2, \start, \tmp2
-9997:
-USER(\label, ic	ivau, \tmp2)			// invalidate I line PoU
+.Licache_op\@:
+	ic	ivau, \tmp2			// invalidate I line PoU
 	add	\tmp2, \tmp2, \tmp1
 	cmp	\tmp2, \end
-	b.lo	9997b
+	b.lo	.Licache_op\@
 	dsb	ish
 	isb
+
+	_cond_extable .Licache_op\@, \fixup
 	.endm
 
 /*