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Revert "arm64: kernel: add support for cpu cache information"

PATCH New Alex Van Brunt 2 participants 5 messages Oct 29, 2015 – Oct 30, 2015

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Alex Van Brunt

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#0 lore raw

PATCH v2 1/4 Revert "arm64: kernel: add support for cpu cache information"

This reverts commit 5d425c18653731af62831d30a4fa023d532657a9.

This reverts a patch that attempt to query the CPU for cache geometry. It relied on NumSets and LineSize fields of CCSIDR to determine the cache geometry. However, the architectural documentation for these registers forbids such use:
The parameters NumSets, Associativity, and LineSize in these registers define the architecturally visible parameters that are required for the cache maintenance by Set/Way instructions. They are not guaranteed to represent the actual microarchitectural features of a design. You cannot make any inference about the actual sizes of caches based on these parameters.

Signed-off-by Alex Van Brunt <[email protected]>
Cc <[email protected]>
---
 arch/arm64/include/asm/cachetype.h |  29 ++-------
 arch/arm64/kernel/Makefile         |   2 +-
 arch/arm64/kernel/cacheinfo.c      | 128 -------------------------------------
 arch/arm64/kernel/cpuinfo.c        |  12 ++++
 4 files changed, 19 insertions(+), 152 deletions(-)
 delete mode 100644 arch/arm64/kernel/cacheinfo.c
arch/arm64/include/asm/cachetype.h +6 -23
index da2fc9e..4c631a0 100644
@@ -39,41 +39,24 @@
 
 extern unsigned long __icache_flags;
 
-/*
- * NumSets, bits[27:13] - (Number of sets in cache) - 1
- * Associativity, bits[12:3] - (Associativity of cache) - 1
- * LineSize, bits[2:0] - (Log2(Number of words in cache line)) - 2
- */
-#define CCSIDR_EL1_WRITE_THROUGH	BIT(31)
-#define CCSIDR_EL1_WRITE_BACK		BIT(30)
-#define CCSIDR_EL1_READ_ALLOCATE	BIT(29)
-#define CCSIDR_EL1_WRITE_ALLOCATE	BIT(28)
 #define CCSIDR_EL1_LINESIZE_MASK	0x7
 #define CCSIDR_EL1_LINESIZE(x)		((x) & CCSIDR_EL1_LINESIZE_MASK)
-#define CCSIDR_EL1_ASSOCIATIVITY_SHIFT	3
-#define CCSIDR_EL1_ASSOCIATIVITY_MASK	0x3ff
-#define CCSIDR_EL1_ASSOCIATIVITY(x)	\
-	(((x) >> CCSIDR_EL1_ASSOCIATIVITY_SHIFT) & CCSIDR_EL1_ASSOCIATIVITY_MASK)
+
 #define CCSIDR_EL1_NUMSETS_SHIFT	13
-#define CCSIDR_EL1_NUMSETS_MASK		0x7fff
+#define CCSIDR_EL1_NUMSETS_MASK		(0x7fff << CCSIDR_EL1_NUMSETS_SHIFT)
 #define CCSIDR_EL1_NUMSETS(x) \
-	(((x) >> CCSIDR_EL1_NUMSETS_SHIFT) & CCSIDR_EL1_NUMSETS_MASK)
-
-#define CACHE_LINESIZE(x)	(16 << CCSIDR_EL1_LINESIZE(x))
-#define CACHE_NUMSETS(x)	(CCSIDR_EL1_NUMSETS(x) + 1)
-#define CACHE_ASSOCIATIVITY(x)	(CCSIDR_EL1_ASSOCIATIVITY(x) + 1)
+	(((x) & CCSIDR_EL1_NUMSETS_MASK) >> CCSIDR_EL1_NUMSETS_SHIFT)
 
-extern u64 __attribute_const__ cache_get_ccsidr(u64 csselr);
+extern u64 __attribute_const__ icache_get_ccsidr(void);
 
-/* Helpers for Level 1 Instruction cache csselr = 1L */
 static inline int icache_get_linesize(void)
 {
-	return CACHE_LINESIZE(cache_get_ccsidr(1L));
+	return 16 << CCSIDR_EL1_LINESIZE(icache_get_ccsidr());
 }
 
 static inline int icache_get_numsets(void)
 {
-	return CACHE_NUMSETS(cache_get_ccsidr(1L));
+	return 1 + CCSIDR_EL1_NUMSETS(icache_get_ccsidr());
 }
 
 /*
arch/arm64/kernel/Makefile +1 -1
index 22dc9bc..abcf663 100644
@@ -17,7 +17,7 @@ arm64-obj-y		:= debug-monitors.o entry.o irq.o fpsimd.o		\
 			   sys.o stacktrace.o time.o traps.o io.o vdso.o	\
 			   hyp-stub.o psci.o psci-call.o cpu_ops.o insn.o	\
 			   return_address.o cpuinfo.o cpu_errata.o		\
-			   cpufeature.o alternative.o cacheinfo.o		\
+			   cpufeature.o alternative.o				\
 			   smp.o smp_spin_table.o topology.o
 
 arm64-obj-$(CONFIG_COMPAT)		+= sys32.o kuser32.o signal32.o 	\
arch/arm64/kernel/cacheinfo.c deleted +0 -128

128 lines not on this page · raw message

arch/arm64/kernel/cpuinfo.c +12 -0
index 75d5a86..540177a 100644
@@ -254,3 +254,15 @@ void __init cpuinfo_store_boot_cpu(void)
 
 	boot_cpu_data = *info;
 }
+
+u64 __attribute_const__ icache_get_ccsidr(void)
+{
+	u64 ccsidr;
+
+	WARN_ON(preemptible());
+
+	/* Select L1 I-cache and read its size ID register */
+	asm("msr csselr_el1, %1; isb; mrs %0, ccsidr_el1"
+	    : "=r"(ccsidr) : "r"(1L));
+	return ccsidr;
+}
Signature · 1 line
2.1.4
author
#1 lore raw

PATCH v2 2/4 Revert "arm64: don't flag non-aliasing VIPT I-caches as aliasing"

This reverts commit 169c018de7b6d376f821f9fae0ab23dc5c7bb549.

The reverted commit attempted to use the cache geometry as reported in CCSIDR to determine if there can be aliasing in the instruction cache. There were two problems with this:

1. CCSIDR_EL1 does not report the actual cache geometry. The architectural documentation for this register says:
The parameters NumSets, Associativity, and LineSize in these registers define the architecturally visible parameters that are required for the cache maintenance by Set/Way instructions. They are not guaranteed to represent the actual microarchitectural features of a design. You cannot make any inference about the actual sizes of caches based on these parameters.

2. The architectural definition of VIPT and PIPT as reported by CTR_EL0 is described in terms of the observable behavior rather than the inner workings of the cache hardware. The difference in the definition of VIPT and PIPT is that VIPT requires invalidating the entire instruction cache to avoid aliasing.

Therefore, even if the cache geometry was known, it is not possible to assume that there is no aliasing.

Signed-off-by Alex Van Brunt <[email protected]>
Cc <[email protected]>
---
 arch/arm64/kernel/cpuinfo.c | 14 ++------------
 1 file changed, 2 insertions(+), 12 deletions(-)
arch/arm64/kernel/cpuinfo.c +2 -12
index 540177a..e0c6c8c 100644
@@ -51,18 +51,8 @@ static void cpuinfo_detect_icache_policy(struct cpuinfo_arm64 *info)
 	unsigned int cpu = smp_processor_id();
 	u32 l1ip = CTR_L1IP(info->reg_ctr);
 
-	if (l1ip != ICACHE_POLICY_PIPT) {
-		/*
-		 * VIPT caches are non-aliasing if the VA always equals the PA
-		 * in all bit positions that are covered by the index. This is
-		 * the case if the size of a way (# of sets * line size) does
-		 * not exceed PAGE_SIZE.
-		 */
-		u32 waysize = icache_get_numsets() * icache_get_linesize();
-
-		if (l1ip != ICACHE_POLICY_VIPT || waysize > PAGE_SIZE)
-			set_bit(ICACHEF_ALIASING, &__icache_flags);
-	}
+	if (l1ip != ICACHE_POLICY_PIPT)
+		set_bit(ICACHEF_ALIASING, &__icache_flags);
 	if (l1ip == ICACHE_POLICY_AIVIVT)
 		set_bit(ICACHEF_AIVIVT, &__icache_flags);
Signature · 1 line
2.1.4
author
#2 lore raw

PATCH v2 3/4 Revert "arm64: add helper functions to read I-cache attributes"

In reply to Alex Van Brunt

This reverts commit 80c517b0ff71a4c874fed9196fd990d2d9e911f3.

This reverts a patch that attempt to query the CPU for cache geometry. It
relied on NumSets and LineSize fields of CCSIDR to determine the cache geometry. However, the architectural documentation for these registers forbids such use:
The parameters NumSets, Associativity, and LineSize in these
registers define the architecturally visible parameters that are
required for the cache maintenance by Set/Way instructions. They are
not guaranteed to represent the actual microarchitectural features
of a design. You cannot make any inference about the actual sizes of
caches based on these parameters.

Signed-off-by Alex Van Brunt <[email protected]>
Cc <[email protected]>
---
 arch/arm64/include/asm/cachetype.h | 20 --------------------
 arch/arm64/kernel/cpuinfo.c        | 14 --------------
 2 files changed, 34 deletions(-)
arch/arm64/include/asm/cachetype.h +0 -20
index 4c631a0..7a2e076 100644
@@ -39,26 +39,6 @@
 
 extern unsigned long __icache_flags;
 
-#define CCSIDR_EL1_LINESIZE_MASK	0x7
-#define CCSIDR_EL1_LINESIZE(x)		((x) & CCSIDR_EL1_LINESIZE_MASK)
-
-#define CCSIDR_EL1_NUMSETS_SHIFT	13
-#define CCSIDR_EL1_NUMSETS_MASK		(0x7fff << CCSIDR_EL1_NUMSETS_SHIFT)
-#define CCSIDR_EL1_NUMSETS(x) \
-	(((x) & CCSIDR_EL1_NUMSETS_MASK) >> CCSIDR_EL1_NUMSETS_SHIFT)
-
-extern u64 __attribute_const__ icache_get_ccsidr(void);
-
-static inline int icache_get_linesize(void)
-{
-	return 16 << CCSIDR_EL1_LINESIZE(icache_get_ccsidr());
-}
-
-static inline int icache_get_numsets(void)
-{
-	return 1 + CCSIDR_EL1_NUMSETS(icache_get_ccsidr());
-}
-
 /*
  * Whilst the D-side always behaves as PIPT on AArch64, aliasing is
  * permitted in the I-cache.
arch/arm64/kernel/cpuinfo.c +0 -14
index e0c6c8c..ae04ac1 100644
@@ -21,10 +21,8 @@
 #include <asm/cpufeature.h>
 
 #include <linux/bitops.h>
-#include <linux/bug.h>
 #include <linux/init.h>
 #include <linux/kernel.h>
-#include <linux/preempt.h>
 #include <linux/printk.h>
 #include <linux/smp.h>
 

@@ -244,15 +242,3 @@ void __init cpuinfo_store_boot_cpu(void)
 
 	boot_cpu_data = *info;
 }
-
-u64 __attribute_const__ icache_get_ccsidr(void)
-{
-	u64 ccsidr;
-
-	WARN_ON(preemptible());
-
-	/* Select L1 I-cache and read its size ID register */
-	asm("msr csselr_el1, %1; isb; mrs %0, ccsidr_el1"
-	    : "=r"(ccsidr) : "r"(1L));
-	return ccsidr;
-}
Signature · 1 line
2.1.4
author
#3 lore raw

PATCH v2 4/4 arm64: document the cache policy behavior

In reply to Alex Van Brunt

Add a comment that clairfies how the kernel should behave given the cache policy reported by the CPU.

Signed-off-by Alex Van Brunt <[email protected]>
Cc <[email protected]>
---
 arch/arm64/kernel/cpuinfo.c | 8 ++++++++
 1 file changed, 8 insertions(+)
arch/arm64/kernel/cpuinfo.c +8 -0
index ae04ac1..bf7e5e2 100644
@@ -49,6 +49,14 @@ static void cpuinfo_detect_icache_policy(struct cpuinfo_arm64 *info)
 	unsigned int cpu = smp_processor_id();
 	u32 l1ip = CTR_L1IP(info->reg_ctr);
 
+	/*
+	 * The ARM architecture defines PIPT, VIPT and AIVIVT in terms of the
+	 * the observable behavior not how the CPU implements the policy.
+	 * Specifically, the policies differentiate the correct way to
+	 * invalidate the cache. The definitions say that the only
+	 * architecturally guaranteed way to invalidate a VIPT or AIVIVT
+	 * instruction cache is to invalidate the entire instruction cache.
+	 */
 	if (l1ip != ICACHE_POLICY_PIPT)
 		set_bit(ICACHEF_ALIASING, &__icache_flags);
 	if (l1ip == ICACHE_POLICY_AIVIVT)
Signature · 1 line
2.1.4
#4 lore raw

PATCH v2 4/4 arm64: document the cache policy behavior

Quoted 1 line · Alex Van Brunt

Add a comment that clairfies how the kernel should behave given the cache

clarifies

Quoted 13 lines

policy reported by the CPU.

Signed-off-by Alex Van Brunt <[email protected]>
Cc <[email protected]>
---
 arch/arm64/kernel/cpuinfo.c | 8 ++++++++
 1 file changed, 8 insertions(+)
arch/arm64/kernel/cpuinfo.c +0 -0
index ae04ac1..bf7e5e2 100644

arch/arm64/kernel/cpuinfo.c static void cpuinfo_detect_icache_policy(struct cpuinfo_arm64 *info) · line 53

Quoted 5 lines
arch/arm64/kernel/cpuinfo.c +2 -0
@@ -49,6 +49,14 @@ static void cpuinfo_detect_icache_policy(struct cpuinfo_arm64 *info)
 	unsigned int cpu = smp_processor_id();
 	u32 l1ip = CTR_L1IP(info->reg_ctr);
 
+	/*
+	 * The ARM architecture defines PIPT, VIPT and AIVIVT in terms of the

-the

arch/arm64/kernel/cpuinfo.c static void cpuinfo_detect_icache_policy(struct cpuinfo_arm64 *info) · line 54

Quoted 1 line
arch/arm64/kernel/cpuinfo.c +1 -0
+	 * the observable behavior not how the CPU implements the policy.

s/not/rather than/

arch/arm64/kernel/cpuinfo.c static void cpuinfo_detect_icache_policy(struct cpuinfo_arm64 *info) · line 62

Quoted 8 lines
arch/arm64/kernel/cpuinfo.c +5 -0
+	 * Specifically, the policies differentiate the correct way to
+	 * invalidate the cache. The definitions say that the only
+	 * architecturally guaranteed way to invalidate a VIPT or AIVIVT
+	 * instruction cache is to invalidate the entire instruction cache.
+	 */
 	if (l1ip != ICACHE_POLICY_PIPT)
 		set_bit(ICACHEF_ALIASING, &__icache_flags);
 	if (l1ip == ICACHE_POLICY_AIVIVT)

With the minor cosmetic changes:

Acked-by Will Deacon <[email protected]>

although I don't see how we can really apply this given that we're not planning to revert the cache geometry stuff. Maybe you could spin a separate series just addressing the aliasing I-cache detection, then we can build on top of that?

Will