[PATCH 8/8] arm64: Work around systems with mismatched cache line sizes
From: Suzuki K Poulose
Date: Thu Aug 18 2016 - 09:11:51 EST
Systems with differing CPU i-cache/d-cache line sizes can cause
problems with the cache management by software when the execution
is migrated from one to another. Usually, the application reads
the cache size on a CPU and then uses that length to perform cache
operations. However, if it gets migrated to another CPU with a smaller
cache line size, things could go completely wrong. To prevent such
cases, always use the smallest cache line size among the CPUs. The
kernel CPU feature infrastructure already keeps track of the safe
value for all CPUID registers including CTR. This patch works around
the problem by :
For kernel, dynamically patch the kernel to read the cache size
from the system wide copy of CTR_EL0.
For applications, trap read accesses to CTR_EL0 (by clearing the SCTLR.UCT)
and emulate the mrs instruction to return the system wide safe value
of CTR_EL0.
For faster access (i.e, avoiding to lookup the system wide value of CTR_EL0
via read_system_reg), we keep track of the pointer to table entry for
CTR_EL0 in the CPU feature infrastructure.
Cc: Mark Rutland <mark.rutland@xxxxxxx>
Cc: Andre Przywara <andre.przywara@xxxxxxx>
Cc: Will Deacon <will.deacon@xxxxxxx>
Cc: Catalin Marinas <catalin.marinas@xxxxxxx>
Signed-off-by: Suzuki K Poulose <suzuki.poulose@xxxxxxx>
---
arch/arm64/include/asm/assembler.h | 25 +++++++++++++++++++++++--
arch/arm64/include/asm/cpufeature.h | 4 +++-
arch/arm64/include/asm/esr.h | 8 ++++++++
arch/arm64/include/asm/sysreg.h | 1 +
arch/arm64/kernel/asm-offsets.c | 2 ++
arch/arm64/kernel/cpu_errata.c | 22 ++++++++++++++++++++++
arch/arm64/kernel/cpufeature.c | 9 +++++++++
arch/arm64/kernel/traps.c | 14 ++++++++++++++
8 files changed, 82 insertions(+), 3 deletions(-)
diff --git a/arch/arm64/include/asm/assembler.h b/arch/arm64/include/asm/assembler.h
index a4bb3f5..66bd268 100644
--- a/arch/arm64/include/asm/assembler.h
+++ b/arch/arm64/include/asm/assembler.h
@@ -216,6 +216,21 @@ lr .req x30 // link register
.macro mmid, rd, rn
ldr \rd, [\rn, #MM_CONTEXT_ID]
.endm
+/*
+ * read_ctr - read CTR_EL0. If the system has mismatched
+ * cache line sizes, provide the system wide safe value.
+ */
+ .macro read_ctr, reg
+alternative_if_not ARM64_MISMATCHED_CACHE_LINE_SIZE
+ mrs \reg, ctr_el0 // read CTR
+ nop
+ nop
+alternative_else
+ ldr_l \reg, sys_ctr_ftr // Read system wide safe CTR value
+ ldr \reg, [\reg, #ARM64_FTR_SYSVAL] // from sys_ctr_ftr->sys_val
+alternative_endif
+ .endm
+
/*
* raw_dcache_line_size - get the minimum D-cache line size on this CPU
@@ -232,7 +247,10 @@ lr .req x30 // link register
* dcache_line_size - get the safe D-cache line size across all CPUs
*/
.macro dcache_line_size, reg, tmp
- raw_dcache_line_size \reg, \tmp
+ read_ctr \tmp
+ ubfm \tmp, \tmp, #16, #19 // cache line size encoding
+ mov \reg, #4 // bytes per word
+ lsl \reg, \reg, \tmp // actual cache line size
.endm
/*
@@ -250,7 +268,10 @@ lr .req x30 // link register
* icache_line_size - get the safe I-cache line size across all CPUs
*/
.macro icache_line_size, reg, tmp
- raw_icache_line_size \reg, \tmp
+ read_ctr \tmp
+ and \tmp, \tmp, #0xf // cache line size encoding
+ mov \reg, #4 // bytes per word
+ lsl \reg, \reg, \tmp // actual cache line size
.endm
/*
diff --git a/arch/arm64/include/asm/cpufeature.h b/arch/arm64/include/asm/cpufeature.h
index 692b8d3..e99f2af 100644
--- a/arch/arm64/include/asm/cpufeature.h
+++ b/arch/arm64/include/asm/cpufeature.h
@@ -37,8 +37,9 @@
#define ARM64_WORKAROUND_CAVIUM_27456 12
#define ARM64_HAS_32BIT_EL0 13
#define ARM64_HYP_OFFSET_LOW 14
+#define ARM64_MISMATCHED_CACHE_LINE_SIZE 15
-#define ARM64_NCAPS 15
+#define ARM64_NCAPS 16
#ifndef __ASSEMBLY__
@@ -109,6 +110,7 @@ struct arm64_cpu_capabilities {
};
extern DECLARE_BITMAP(cpu_hwcaps, ARM64_NCAPS);
+extern struct arm64_ftr_reg *sys_ctr_ftr;
bool this_cpu_has_cap(unsigned int cap);
diff --git a/arch/arm64/include/asm/esr.h b/arch/arm64/include/asm/esr.h
index 2a8f6c3..51aea89 100644
--- a/arch/arm64/include/asm/esr.h
+++ b/arch/arm64/include/asm/esr.h
@@ -139,6 +139,9 @@
((Op2) << ESR_ELx_SYS64_ISS_Op2_SHIFT) | \
((CRn) << ESR_ELx_SYS64_ISS_CRn_SHIFT) | \
((CRm) << ESR_ELx_SYS64_ISS_CRm_SHIFT))
+
+#define ESR_ELx_SYS64_ISS_SYS_OP_MASK (ESR_ELx_SYS64_ISS_SYS_MASK | \
+ ESR_ELx_SYS64_ISS_DIR_MASK)
/*
* User space cache operations have the following sysreg encoding
* in System instructions.
@@ -157,6 +160,11 @@
#define ESR_ELx_SYS64_ISS_U_CACHE_OP_VAL \
(ESR_ELx_SYS64_ISS_SYS_VAL(1, 3, 1, 7, 0) | \
ESR_ELx_SYS64_ISS_DIR_WRITE)
+
+#define ESR_ELx_SYS64_ISS_SYS_CTR ESR_ELx_SYS64_ISS_SYS_VAL(3, 3, 1, 0, 0)
+#define ESR_ELx_SYS64_ISS_SYS_CTR_READ (ESR_ELx_SYS64_ISS_SYS_CTR | \
+ ESR_ELx_SYS64_ISS_DIR_READ)
+
#ifndef __ASSEMBLY__
#include <asm/types.h>
diff --git a/arch/arm64/include/asm/sysreg.h b/arch/arm64/include/asm/sysreg.h
index cc06794..4f26ad5 100644
--- a/arch/arm64/include/asm/sysreg.h
+++ b/arch/arm64/include/asm/sysreg.h
@@ -100,6 +100,7 @@
/* SCTLR_EL1 specific flags. */
#define SCTLR_EL1_UCI (1 << 26)
#define SCTLR_EL1_SPAN (1 << 23)
+#define SCTLR_EL1_UCT (1 << 15)
#define SCTLR_EL1_SED (1 << 8)
#define SCTLR_EL1_CP15BEN (1 << 5)
diff --git a/arch/arm64/kernel/asm-offsets.c b/arch/arm64/kernel/asm-offsets.c
index 05070b7..4a2f0f0 100644
--- a/arch/arm64/kernel/asm-offsets.c
+++ b/arch/arm64/kernel/asm-offsets.c
@@ -23,6 +23,7 @@
#include <linux/dma-mapping.h>
#include <linux/kvm_host.h>
#include <linux/suspend.h>
+#include <asm/cpufeature.h>
#include <asm/thread_info.h>
#include <asm/memory.h>
#include <asm/smp_plat.h>
@@ -145,5 +146,6 @@ int main(void)
DEFINE(HIBERN_PBE_ORIG, offsetof(struct pbe, orig_address));
DEFINE(HIBERN_PBE_ADDR, offsetof(struct pbe, address));
DEFINE(HIBERN_PBE_NEXT, offsetof(struct pbe, next));
+ DEFINE(ARM64_FTR_SYSVAL, offsetof(struct arm64_ftr_reg, sys_val));
return 0;
}
diff --git a/arch/arm64/kernel/cpu_errata.c b/arch/arm64/kernel/cpu_errata.c
index 5836b3d..621fa7f 100644
--- a/arch/arm64/kernel/cpu_errata.c
+++ b/arch/arm64/kernel/cpu_errata.c
@@ -30,6 +30,21 @@ is_affected_midr_range(const struct arm64_cpu_capabilities *entry, int scope)
entry->midr_range_max);
}
+static bool
+has_mismatched_cache_line_size(const struct arm64_cpu_capabilities *entry,
+ int scope)
+{
+ WARN_ON(scope != SCOPE_LOCAL_CPU || preemptible());
+ return (read_cpuid_cachetype() & sys_ctr_ftr->strict_mask) !=
+ (sys_ctr_ftr->sys_val & sys_ctr_ftr->strict_mask);
+}
+
+static void cpu_enable_trap_ctr_access(void *__unused)
+{
+ /* Clear SCTLR_EL1.UCT */
+ config_sctlr_el1(SCTLR_EL1_UCT, 0);
+}
+
#define MIDR_RANGE(model, min, max) \
.def_scope = SCOPE_LOCAL_CPU, \
.matches = is_affected_midr_range, \
@@ -108,6 +123,13 @@ const struct arm64_cpu_capabilities arm64_errata[] = {
},
#endif
{
+ .desc = "Mismatched cache line size",
+ .capability = ARM64_MISMATCHED_CACHE_LINE_SIZE,
+ .matches = has_mismatched_cache_line_size,
+ .def_scope = SCOPE_LOCAL_CPU,
+ .enable = cpu_enable_trap_ctr_access,
+ },
+ {
}
};
diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
index fcf87ca..c1db313 100644
--- a/arch/arm64/kernel/cpufeature.c
+++ b/arch/arm64/kernel/cpufeature.c
@@ -46,6 +46,13 @@ unsigned int compat_elf_hwcap2 __read_mostly;
DECLARE_BITMAP(cpu_hwcaps, ARM64_NCAPS);
+/*
+ * If we have mismatched cache line sizes, we need to emulate access to
+ * CTRL_EL0. To avoid a lookup everytime (via read_system_reg()), cache
+ * the table entry for CTR_EL0.
+ */
+struct arm64_ftr_reg *sys_ctr_ftr;
+
#define __ARM64_FTR_BITS(SIGNED, STRICT, TYPE, SHIFT, WIDTH, SAFE_VAL) \
{ \
.sign = SIGNED, \
@@ -461,6 +468,8 @@ void __init init_cpu_features(struct cpuinfo_arm64 *info)
init_cpu_ftr_reg(SYS_MVFR2_EL1, info->reg_mvfr2);
}
+ /* Keep track of the CTR feature register */
+ sys_ctr_ftr = get_arm64_ftr_reg(SYS_CTR_EL0);
}
static void update_cpu_ftr_reg(struct arm64_ftr_reg *reg, u64 new)
diff --git a/arch/arm64/kernel/traps.c b/arch/arm64/kernel/traps.c
index 93c5287..db2d6cb 100644
--- a/arch/arm64/kernel/traps.c
+++ b/arch/arm64/kernel/traps.c
@@ -480,6 +480,14 @@ static void user_cache_maint_handler(unsigned int esr, struct pt_regs *regs)
regs->pc += 4;
}
+static void ctr_read_handler(unsigned int esr, struct pt_regs *regs)
+{
+ int rt = (esr & ESR_ELx_SYS64_ISS_RT_MASK) >> ESR_ELx_SYS64_ISS_RT_SHIFT;
+
+ regs->regs[rt] = sys_ctr_ftr->sys_val;
+ regs->pc += 4;
+}
+
struct sys64_hook {
unsigned int esr_mask;
unsigned int esr_val;
@@ -492,6 +500,12 @@ static struct sys64_hook sys64_hooks[] = {
.esr_val = ESR_ELx_SYS64_ISS_U_CACHE_OP_VAL,
.handler = user_cache_maint_handler,
},
+ {
+ /* Trap read access to CTR_EL0 */
+ .esr_mask = ESR_ELx_SYS64_ISS_SYS_OP_MASK,
+ .esr_val = ESR_ELx_SYS64_ISS_SYS_CTR_READ,
+ .handler = ctr_read_handler,
+ },
{},
};
--
2.7.4