RISC-V: Flush I$ when making a dirty page executable

The RISC-V ISA allows for instruction caches that are not coherent WRT
stores, even on a single hart.  As a result, we need to explicitly flush
the instruction cache whenever marking a dirty page as executable in
order to preserve the correct system behavior.

Local instruction caches aren't that scary (our implementations actually
flush the cache, but RISC-V is defined to allow higher-performance
implementations to exist), but RISC-V defines no way to perform an
instruction cache shootdown.  When explicitly asked to do so we can
shoot down remote instruction caches via an IPI, but this is a bit on
the slow side.

Instead of requiring an IPI to all harts whenever marking a page as
executable, we simply flush the currently running harts.  In order to
maintain correct behavior, we additionally mark every other hart as
needing a deferred instruction cache which will be taken before anything
runs on it.

Signed-off-by: Andrew Waterman <andrew@sifive.com>
Signed-off-by: Palmer Dabbelt <palmer@sifive.com>

1 files changed, 4 insertions, 0 deletions

diff --git a/arch/riscv/include/asm/mmu.h b/arch/riscv/include/asm/mmu.h
index 66805cba9a27..5df2dccdba12 100644
--- a/arch/riscv/include/asm/mmu.h
+++ b/arch/riscv/include/asm/mmu.h
@@ -19,6 +19,10 @@
 
 typedef struct {
 	void *vdso;
+#ifdef CONFIG_SMP
+	/* A local icache flush is needed before user execution can resume. */
+	cpumask_t icache_stale_mask;
+#endif
 } mm_context_t;
 
 #endif /* __ASSEMBLY__ */