Merge patch series "riscv: Create and document PR_RISCV_SET_ICACHE_FLUSH_CTX prctl"

Charlie Jenkins <charlie@rivosinc.com> says:

Improve the performance of icache flushing by creating a new prctl flag
PR_RISCV_SET_ICACHE_FLUSH_CTX. The interface is left generic to allow
for future expansions such as with the proposed J extension [1].

Documentation is also provided to explain the use case.

Patch sent to add PR_RISCV_SET_ICACHE_FLUSH_CTX to man-pages [2].

[1] https://github.com/riscv/riscv-j-extension
[2] https://lore.kernel.org/linux-man/20240124-fencei_prctl-v1-1-0bddafcef331@rivosinc.com

* b4-shazam-merge:
  cpumask: Add assign cpu
  documentation: Document PR_RISCV_SET_ICACHE_FLUSH_CTX prctl
  riscv: Include riscv_set_icache_flush_ctx prctl
  riscv: Remove unnecessary irqflags processor.h include

Link: https://lore.kernel.org/r/20240312-fencei-v13-0-4b6bdc2bbf32@rivosinc.com
Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>

1 files changed, 11 insertions, 8 deletions

diff --git a/arch/riscv/mm/context.c b/arch/riscv/mm/context.c
index ba8eb3944687..9b6db024103b 100644
--- a/arch/riscv/mm/context.c
+++ b/arch/riscv/mm/context.c
@@ -15,6 +15,7 @@
 #include <asm/tlbflush.h>
 #include <asm/cacheflush.h>
 #include <asm/mmu_context.h>
+#include <asm/switch_to.h>
 
 #ifdef CONFIG_MMU
 
@@ -297,21 +298,23 @@ static inline void set_mm(struct mm_struct *prev,
  *
  * The "cpu" argument must be the current local CPU number.
  */
-static inline void flush_icache_deferred(struct mm_struct *mm, unsigned int cpu)
+static inline void flush_icache_deferred(struct mm_struct *mm, unsigned int cpu,
+					 struct task_struct *task)
 {
 #ifdef CONFIG_SMP
-	cpumask_t *mask = &mm->context.icache_stale_mask;
-
-	if (cpumask_test_cpu(cpu, mask)) {
-		cpumask_clear_cpu(cpu, mask);
+	if (cpumask_test_and_clear_cpu(cpu, &mm->context.icache_stale_mask)) {
 		/*
 		 * Ensure the remote hart's writes are visible to this hart.
 		 * This pairs with a barrier in flush_icache_mm.
 		 */
 		smp_mb();
-		local_flush_icache_all();
-	}
 
+		/*
+		 * If cache will be flushed in switch_to, no need to flush here.
+		 */
+		if (!(task && switch_to_should_flush_icache(task)))
+			local_flush_icache_all();
+	}
 #endif
 }
 
@@ -334,5 +337,5 @@ void switch_mm(struct mm_struct *prev, struct mm_struct *next,
 
 	set_mm(prev, next, cpu);
 
-	flush_icache_deferred(next, cpu);
+	flush_icache_deferred(next, cpu, task);
 }