arm64: add Cortex-A53 cache errata workaround

The ARM errata 819472, 826319, 827319 and 824069 define the same
workaround for these hardware issues in certain Cortex-A53 parts.
Use the new alternatives framework and the CPU MIDR detection to
patch "cache clean" into "cache clean and invalidate" instructions if
an affected CPU is detected at runtime.
Signed-off-by: Andre Przywara <andre.przywara@arm.com>
[will: add __maybe_unused to squash gcc warning]
Signed-off-by: Will Deacon <will.deacon@arm.com>

arch/arm64/include/asm/alternative-asm.h

@@ -11,6 +11,19 @@
 	.byte \alt_len
 .endm
 
+.macro alternative_insn insn1 insn2 cap
+661:	\insn1
+662:	.pushsection .altinstructions, "a"
+	altinstruction_entry 661b, 663f, \cap, 662b-661b, 664f-663f
+	.popsection
+	.pushsection .altinstr_replacement, "ax"
+663:	\insn2
+664:	.popsection
+	.if ((664b-663b) != (662b-661b))
+		.error "Alternatives instruction length mismatch"
+	.endif
+.endm
+
 #endif  /*  __ASSEMBLY__  */
 
 #endif /* __ASM_ALTERNATIVE_ASM_H */

arch/arm64/include/asm/cpufeature.h

@@ -21,7 +21,11 @@
 #define MAX_CPU_FEATURES	(8 * sizeof(elf_hwcap))
 #define cpu_feature(x)		ilog2(HWCAP_ ## x)
 
-#define NCAPS			0
+#define ARM64_WORKAROUND_CLEAN_CACHE	0
+
+#define NCAPS				1
+
+#ifndef __ASSEMBLY__
 
 extern DECLARE_BITMAP(cpu_hwcaps, NCAPS);
 
@@ -48,4 +52,6 @@ static inline void cpus_set_cap(unsigned int num)
 
 void check_local_cpu_errata(void);
 
+#endif /* __ASSEMBLY__ */
+
 #endif

arch/arm64/include/asm/cputype.h

@@ -57,6 +57,11 @@
 #define MIDR_IMPLEMENTOR(midr)	\
 	(((midr) & MIDR_IMPLEMENTOR_MASK) >> MIDR_IMPLEMENTOR_SHIFT)
 
+#define MIDR_CPU_PART(imp, partnum) \
+	(((imp)			<< MIDR_IMPLEMENTOR_SHIFT) | \
+	(0xf			<< MIDR_ARCHITECTURE_SHIFT) | \
+	((partnum)		<< MIDR_PARTNUM_SHIFT))
+
 #define ARM_CPU_IMP_ARM		0x41
 #define ARM_CPU_IMP_APM		0x50
 

arch/arm64/kernel/cpu_errata.c

@@ -23,6 +23,8 @@
 #include <asm/cputype.h>
 #include <asm/cpufeature.h>
 
+#define MIDR_CORTEX_A53 MIDR_CPU_PART(ARM_CPU_IMP_ARM, ARM_CPU_PART_CORTEX_A53)
+
 /*
  * Add a struct or another datatype to the union below if you need
  * different means to detect an affected CPU.
@@ -39,8 +41,37 @@ struct arm64_cpu_capabilities {
 	};
 };
 
+#define CPU_MODEL_MASK (MIDR_IMPLEMENTOR_MASK | MIDR_PARTNUM_MASK | \
+			MIDR_ARCHITECTURE_MASK)
+
+static bool __maybe_unused
+is_affected_midr_range(struct arm64_cpu_capabilities *entry)
+{
+	u32 midr = read_cpuid_id();
+
+	if ((midr & CPU_MODEL_MASK) != entry->midr_model)
+		return false;
+
+	midr &= MIDR_REVISION_MASK | MIDR_VARIANT_MASK;
+
+	return (midr >= entry->midr_range_min && midr <= entry->midr_range_max);
+}
+
+#define MIDR_RANGE(model, min, max) \
+	.is_affected = is_affected_midr_range, \
+	.midr_model = model, \
+	.midr_range_min = min, \
+	.midr_range_max = max
+
 struct arm64_cpu_capabilities arm64_errata[] = {
-	{}
+	{
+	/* Cortex-A53 r0p[012] */
+		.desc = "ARM errata 826319, 827319, 824069",
+		.capability = ARM64_WORKAROUND_CLEAN_CACHE,
+		MIDR_RANGE(MIDR_CORTEX_A53, 0x00, 0x02),
+	},
+	{
+	}
 };
 
 void check_local_cpu_errata(void)

arch/arm64/mm/cache.S

@@ -20,6 +20,8 @@
 #include <linux/linkage.h>
 #include <linux/init.h>
 #include <asm/assembler.h>
+#include <asm/cpufeature.h>
+#include <asm/alternative-asm.h>
 
 #include "proc-macros.S"
 
@@ -210,7 +212,7 @@ __dma_clean_range:
 	dcache_line_size x2, x3
 	sub	x3, x2, #1
 	bic	x0, x0, x3
-1:	dc	cvac, x0			// clean D / U line
+1:	alternative_insn "dc cvac, x0", "dc civac, x0", ARM64_WORKAROUND_CLEAN_CACHE
 	add	x0, x0, x2
 	cmp	x0, x1
 	b.lo	1b