From 08f051eda33b51e8ee0f45f05bcfe49d0f0caf6b Mon Sep 17 00:00:00 2001 From: Andrew Waterman Date: Wed, 25 Oct 2017 14:30:32 -0700 Subject: 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 Signed-off-by: Palmer Dabbelt --- arch/riscv/kernel/smp.c | 48 ++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 48 insertions(+) (limited to 'arch/riscv/kernel/smp.c') diff --git a/arch/riscv/kernel/smp.c b/arch/riscv/kernel/smp.c index b4a71ec..1b27ade 100644 --- a/arch/riscv/kernel/smp.c +++ b/arch/riscv/kernel/smp.c @@ -108,3 +108,51 @@ void smp_send_reschedule(int cpu) { send_ipi_message(cpumask_of(cpu), IPI_RESCHEDULE); } + +/* + * Performs an icache flush for the given MM context. RISC-V has no direct + * mechanism for instruction cache shoot downs, so instead we send an IPI that + * informs the remote harts they need to flush their local instruction caches. + * To avoid pathologically slow behavior in a common case (a bunch of + * single-hart processes on a many-hart machine, ie 'make -j') we avoid the + * IPIs for harts that are not currently executing a MM context and instead + * schedule a deferred local instruction cache flush to be performed before + * execution resumes on each hart. + */ +void flush_icache_mm(struct mm_struct *mm, bool local) +{ + unsigned int cpu; + cpumask_t others, *mask; + + preempt_disable(); + + /* Mark every hart's icache as needing a flush for this MM. */ + mask = &mm->context.icache_stale_mask; + cpumask_setall(mask); + /* Flush this hart's I$ now, and mark it as flushed. */ + cpu = smp_processor_id(); + cpumask_clear_cpu(cpu, mask); + local_flush_icache_all(); + + /* + * Flush the I$ of other harts concurrently executing, and mark them as + * flushed. + */ + cpumask_andnot(&others, mm_cpumask(mm), cpumask_of(cpu)); + local |= cpumask_empty(&others); + if (mm != current->active_mm || !local) + sbi_remote_fence_i(others.bits); + else { + /* + * It's assumed that at least one strongly ordered operation is + * performed on this hart between setting a hart's cpumask bit + * and scheduling this MM context on that hart. Sending an SBI + * remote message will do this, but in the case where no + * messages are sent we still need to order this hart's writes + * with flush_icache_deferred(). + */ + smp_mb(); + } + + preempt_enable(); +} -- cgit v1.1