[PATCH] arm64: Clarify ARM64_WORKAROUND_REPEAT_TLBI semantics

[PATCH] arm64: Clarify ARM64_WORKAROUND_REPEAT_TLBI semantics

[Mark Rutland]

Will notes that the ARM64_WORKAROUND_REPEAT_TLBI name is potentially
misleading, and that it would be nice to rename that and add some
documentation. See:

  https://lore.kernel.org/linux-arm-kernel/ajKn_Pt50CmOUrsP@willie-the-truck/

To that end, I've renamed the Kconfig symbol and hwcap from:

  [CONFIG_]ARM64_WORKAROUND_REPEAT_TLBI

... to:

  [CONFIG_]ARM64_WORKAROUND_REPEAT_TLBI_SYNC

... and I've added some rationale alongside the Kconfig. As the Kconfig
symbol isn't user selectable, the usual 'help' section won't appear in
menuconfig, so I've added this as a comment.

The rename was scripted with:

  git grep -l REPEAT_TLBI | while read F; do
    sed -i '{ s/WORKAROUND_REPEAT_TLBI\>/WORKAROUND_REPEAT_TLBI_SYNC/g }' $F;
  done

Bikeshedding-wise, I considered a few names, including:

* ARM64_WORKAROUND_REPEAT_TLBI_SYNC
* ARM64_WORKAROUND_TLBI_REPEAT_SYNC
* ARM64_WORKAROUND_BROADCAST_TLBI_REPEAT_SYNC

... and I settled on ARM64_WORKAROUND_REPEAT_TLBI_SYNC to try keep
things simple, and to avoid unnecessary churn caused by moving
definitions to retain alphabetical order. I'm happy to defer to Will and
Catalin's preference.

Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Will Deacon <will@kernel.org>
---
 arch/arm64/Kconfig                | 34 +++++++++++++++++++++++++------
 arch/arm64/include/asm/cpucaps.h  |  4 ++--
 arch/arm64/include/asm/tlbflush.h |  2 +-
 arch/arm64/kernel/cpu_errata.c    |  6 +++---
 arch/arm64/tools/cpucaps          |  2 +-
 5 files changed, 35 insertions(+), 13 deletions(-)

diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
index b3afe0688919b..7571104215435 100644
--- a/arch/arm64/Kconfig
+++ b/arch/arm64/Kconfig
@@ -701,12 +701,34 @@ config ARM64_ERRATUM_1530923
 
 	  If unsure, say Y.
 
-config ARM64_WORKAROUND_REPEAT_TLBI
+config ARM64_WORKAROUND_REPEAT_TLBI_SYNC
 	bool
+	# This workaround is (only) suitable for TLB invalidation errata where
+	# all of the following conditions are true:
+	#
+	# - The effects of the errata are only a loss of ordering/completion
+	#   for explicit memory accesses when the TLBI is completed with a DSB.
+	#   The removal of TLB entries is not affected.
+	#
+	#   Note that architecturally, S2-only invalidation does not remove
+	#   combined S1+S2 entries, and does not complete accesses translated
+	#   via those S1+S2 entries. Consequently, where this condition holds,
+	#   the errata do not affect S2-only invalidation.
+	#
+	# - The errata only affect broadcast TLB invalidation operations (e.g.
+	#   TLBI VMALLE1IS), and do not affect local TLB invalidation
+	#   operations (e.g. TLBI VMALLE1).
+	#
+	# - After any number of affected TLBI operations are completed with a
+	#   DSB, the errata can be mitigated by executing a single arbitrary
+	#   broadcast TLBI (which targets an arbitrary translation regime),
+	#   followed by a DSB.
+	#
+	# For more rationale, see commit a8f78680ee6bf795.
 
 config ARM64_ERRATUM_2441007
 	bool "Cortex-A55: Completion of affected memory accesses might not be guaranteed by completion of a TLBI (rare)"
-	select ARM64_WORKAROUND_REPEAT_TLBI
+	select ARM64_WORKAROUND_REPEAT_TLBI_SYNC
 	help
 	  This option adds a workaround for ARM Cortex-A55 erratum #2441007.
 
@@ -722,7 +744,7 @@ config ARM64_ERRATUM_2441007
 
 config ARM64_ERRATUM_1286807
 	bool "Cortex-A76: Modification of the translation table for a virtual address might lead to read-after-read ordering violation (rare)"
-	select ARM64_WORKAROUND_REPEAT_TLBI
+	select ARM64_WORKAROUND_REPEAT_TLBI_SYNC
 	help
 	  This option adds a workaround for ARM Cortex-A76 erratum 1286807.
 
@@ -944,7 +966,7 @@ config ARM64_ERRATUM_2224489
 
 config ARM64_ERRATUM_2441009
 	bool "Cortex-A510: Completion of affected memory accesses might not be guaranteed by completion of a TLBI (rare)"
-	select ARM64_WORKAROUND_REPEAT_TLBI
+	select ARM64_WORKAROUND_REPEAT_TLBI_SYNC
 	help
 	  This option adds a workaround for ARM Cortex-A510 erratum #2441009.
 
@@ -1156,7 +1178,7 @@ config ARM64_ERRATUM_4193714
 config ARM64_ERRATUM_4118414
 	bool "Various: Completion of affected memory accesses might not be guaranteed by completion of a TLBI"
 	default y
-	select ARM64_WORKAROUND_REPEAT_TLBI
+	select ARM64_WORKAROUND_REPEAT_TLBI_SYNC
 	help
 	  This option adds a workaround for the following errata:
 
@@ -1340,7 +1362,7 @@ config QCOM_FALKOR_ERRATUM_1003
 config QCOM_FALKOR_ERRATUM_1009
 	bool "Falkor E1009: Prematurely complete a DSB after a TLBI"
 	default y
-	select ARM64_WORKAROUND_REPEAT_TLBI
+	select ARM64_WORKAROUND_REPEAT_TLBI_SYNC
 	help
 	  On Falkor v1, the CPU may prematurely complete a DSB following a
 	  TLBI xxIS invalidate maintenance operation. Repeat the TLBI operation
diff --git a/arch/arm64/include/asm/cpucaps.h b/arch/arm64/include/asm/cpucaps.h
index 25c61cda901c5..76350b38f0d7a 100644
--- a/arch/arm64/include/asm/cpucaps.h
+++ b/arch/arm64/include/asm/cpucaps.h
@@ -60,8 +60,8 @@ cpucap_is_possible(const unsigned int cap)
 		return IS_ENABLED(CONFIG_CAVIUM_ERRATUM_23154);
 	case ARM64_WORKAROUND_DISABLE_CNP:
 		return IS_ENABLED(CONFIG_ARM64_WORKAROUND_DISABLE_CNP);
-	case ARM64_WORKAROUND_REPEAT_TLBI:
-		return IS_ENABLED(CONFIG_ARM64_WORKAROUND_REPEAT_TLBI);
+	case ARM64_WORKAROUND_REPEAT_TLBI_SYNC:
+		return IS_ENABLED(CONFIG_ARM64_WORKAROUND_REPEAT_TLBI_SYNC);
 	case ARM64_WORKAROUND_SPECULATIVE_SSBS:
 		return IS_ENABLED(CONFIG_ARM64_ERRATUM_3194386);
 	case ARM64_WORKAROUND_4193714:
diff --git a/arch/arm64/include/asm/tlbflush.h b/arch/arm64/include/asm/tlbflush.h
index d52ac8c17190d..bd68ca6df62ba 100644
--- a/arch/arm64/include/asm/tlbflush.h
+++ b/arch/arm64/include/asm/tlbflush.h
@@ -268,7 +268,7 @@ static inline void __tlbi_level(tlbi_op op, u64 addr, u32 level)
 
 #define __repeat_tlbi_sync(op, arg...)						\
 do {										\
-	if (!alternative_has_cap_unlikely(ARM64_WORKAROUND_REPEAT_TLBI))	\
+	if (!alternative_has_cap_unlikely(ARM64_WORKAROUND_REPEAT_TLBI_SYNC))	\
 		break;								\
 	__tlbi(op, ##arg);							\
 	dsb(ish);								\
diff --git a/arch/arm64/kernel/cpu_errata.c b/arch/arm64/kernel/cpu_errata.c
index 1995e1198648e..685077d44ad17 100644
--- a/arch/arm64/kernel/cpu_errata.c
+++ b/arch/arm64/kernel/cpu_errata.c
@@ -309,7 +309,7 @@ static void cpu_enable_impdef_pmuv3_traps(const struct arm64_cpu_capabilities *_
 	sysreg_clear_set_s(SYS_HACR_EL2, 0, BIT(56));
 }
 
-#ifdef CONFIG_ARM64_WORKAROUND_REPEAT_TLBI
+#ifdef CONFIG_ARM64_WORKAROUND_REPEAT_TLBI_SYNC
 static const struct arm64_cpu_capabilities arm64_repeat_tlbi_list[] = {
 #ifdef CONFIG_QCOM_FALKOR_ERRATUM_1009
 	{
@@ -733,10 +733,10 @@ const struct arm64_cpu_capabilities arm64_errata[] = {
 		.match_list = qcom_erratum_1003_list,
 	},
 #endif
-#ifdef CONFIG_ARM64_WORKAROUND_REPEAT_TLBI
+#ifdef CONFIG_ARM64_WORKAROUND_REPEAT_TLBI_SYNC
 	{
 		.desc = "Broken broadcast TLBI completion",
-		.capability = ARM64_WORKAROUND_REPEAT_TLBI,
+		.capability = ARM64_WORKAROUND_REPEAT_TLBI_SYNC,
 		.type = ARM64_CPUCAP_LOCAL_CPU_ERRATUM,
 		.matches = cpucap_multi_entry_cap_matches,
 		.match_list = arm64_repeat_tlbi_list,
diff --git a/arch/arm64/tools/cpucaps b/arch/arm64/tools/cpucaps
index 9b85a84f6fd49..f8368e5d81a8e 100644
--- a/arch/arm64/tools/cpucaps
+++ b/arch/arm64/tools/cpucaps
@@ -124,7 +124,7 @@ WORKAROUND_DISABLE_CNP
 WORKAROUND_PMUV3_IMPDEF_TRAPS
 WORKAROUND_QCOM_FALKOR_E1003
 WORKAROUND_QCOM_ORYON_CNTVOFF
-WORKAROUND_REPEAT_TLBI
+WORKAROUND_REPEAT_TLBI_SYNC
 WORKAROUND_SPECULATIVE_AT
 WORKAROUND_SPECULATIVE_SSBS
 WORKAROUND_SPECULATIVE_UNPRIV_LOAD
-- 
2.30.2

Re: [PATCH] arm64: Clarify ARM64_WORKAROUND_REPEAT_TLBI semantics

[Vladimir Murzin]

Hi Mark,

On 6/29/26 11:09, Mark Rutland wrote:
> Will notes that the ARM64_WORKAROUND_REPEAT_TLBI name is potentially
> misleading, and that it would be nice to rename that and add some
> documentation. See:
> 
>   https://lore.kernel.org/linux-arm-kernel/ajKn_Pt50CmOUrsP@willie-the-truck/
> 
> To that end, I've renamed the Kconfig symbol and hwcap from:
> 
>   [CONFIG_]ARM64_WORKAROUND_REPEAT_TLBI
> 
> ... to:
> 
>   [CONFIG_]ARM64_WORKAROUND_REPEAT_TLBI_SYNC
> 
> ... and I've added some rationale alongside the Kconfig. As the Kconfig
> symbol isn't user selectable, the usual 'help' section won't appear in
> menuconfig, so I've added this as a comment.
> 

Although it won't appear in menuconfig, 3rd party tools that
index config symbols may still consume the help section.
I'm not sure how much we care about such tools...

Cheers
Vladimir