6.6-stable review patch. If anyone has any objections, please let me know.
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From: Will Deacon will@kernel.org
[ Upstream commit cfb00a35786414e7c0e6226b277d9f09657eae74 ]
Although the Arm architecture permits concurrent modification and execution of NOP and branch instructions, it still requires some synchronisation to ensure that other CPUs consistently execute the newly written instruction:
When the modified instructions are observable, each PE that is executing the modified instructions must execute an ISB or perform a context synchronizing event to ensure execution of the modified instructions
Prior to commit f6cc0c501649 ("arm64: Avoid calling stop_machine() when patching jump labels"), the arm64 jump_label patching machinery performed synchronisation using stop_machine() after each modification, however this was problematic when flipping static keys from atomic contexts (namely, the arm_arch_timer CPU hotplug startup notifier) and so we switched to the _nosync() patching routines to avoid "scheduling while atomic" BUG()s during boot.
In hindsight, the analysis of the issue in f6cc0c501649 isn't quite right: it cites the use of IPIs in the default patching routines as the cause of the lockup, whereas stop_machine() does not rely on IPIs and the I-cache invalidation is performed using __flush_icache_range(), which elides the call to kick_all_cpus_sync(). In fact, the blocking wait for other CPUs is what triggers the BUG() and the problem remains even after f6cc0c501649, for example because we could block on the jump_label_mutex. Eventually, the arm_arch_timer driver was fixed to avoid the static key entirely in commit a862fc2254bd ("clocksource/arm_arch_timer: Remove use of workaround static key").
This all leaves the jump_label patching code in a funny situation on arm64 as we do not synchronise with other CPUs to reduce the likelihood of a bug which no longer exists. Consequently, toggling a static key on one CPU cannot be assumed to take effect on other CPUs, leading to potential issues, for example with missing preempt notifiers.
Rather than revert f6cc0c501649 and go back to stop_machine() for each patch site, implement arch_jump_label_transform_apply() and kick all the other CPUs with an IPI at the end of patching.
Cc: Alexander Potapenko glider@google.com Cc: Mark Rutland mark.rutland@arm.com Cc: Marc Zyngier maz@kernel.org Fixes: f6cc0c501649 ("arm64: Avoid calling stop_machine() when patching jump labels") Signed-off-by: Will Deacon will@kernel.org Reviewed-by: Catalin Marinas catalin.marinas@arm.com Reviewed-by: Marc Zyngier maz@kernel.org Link: https://lore.kernel.org/r/20240731133601.3073-1-will@kernel.org Signed-off-by: Catalin Marinas catalin.marinas@arm.com Signed-off-by: Sasha Levin sashal@kernel.org --- arch/arm64/include/asm/jump_label.h | 1 + arch/arm64/kernel/jump_label.c | 11 +++++++++-- 2 files changed, 10 insertions(+), 2 deletions(-)
diff --git a/arch/arm64/include/asm/jump_label.h b/arch/arm64/include/asm/jump_label.h index 6aafbb7899916..4b99159150829 100644 --- a/arch/arm64/include/asm/jump_label.h +++ b/arch/arm64/include/asm/jump_label.h @@ -13,6 +13,7 @@ #include <linux/types.h> #include <asm/insn.h>
+#define HAVE_JUMP_LABEL_BATCH #define JUMP_LABEL_NOP_SIZE AARCH64_INSN_SIZE
static __always_inline bool arch_static_branch(struct static_key * const key, diff --git a/arch/arm64/kernel/jump_label.c b/arch/arm64/kernel/jump_label.c index faf88ec9c48e8..f63ea915d6ad2 100644 --- a/arch/arm64/kernel/jump_label.c +++ b/arch/arm64/kernel/jump_label.c @@ -7,11 +7,12 @@ */ #include <linux/kernel.h> #include <linux/jump_label.h> +#include <linux/smp.h> #include <asm/insn.h> #include <asm/patching.h>
-void arch_jump_label_transform(struct jump_entry *entry, - enum jump_label_type type) +bool arch_jump_label_transform_queue(struct jump_entry *entry, + enum jump_label_type type) { void *addr = (void *)jump_entry_code(entry); u32 insn; @@ -25,4 +26,10 @@ void arch_jump_label_transform(struct jump_entry *entry, }
aarch64_insn_patch_text_nosync(addr, insn); + return true; +} + +void arch_jump_label_transform_apply(void) +{ + kick_all_cpus_sync(); }