[PATCH RFC v3 08/12] arm64: kernel: implement HW breakpoints CPU PM notifier
From: Will Deacon <hidden>
Date: 2013-12-20 17:29:07
Also in:
linux-pm
Hi Lorenzo, On Thu, Nov 21, 2013 at 11:24:15AM +0000, Lorenzo Pieralisi wrote:
When a CPU is shutdown either through CPU idle or suspend to RAM, the content of HW breakpoint registers must be reset or restored to proper values when CPU resume from low power states. This patch adds debug register restore operations to the HW breakpoint control function and implements a CPU PM notifier that allows to restore the content of HW breakpoint registers to allow proper suspend/resume operations.
This looks mostly fine to me, but I have one questions you might be able to answer...
quoted hunk ↗ jump to hunk
@@ -840,18 +847,36 @@ void hw_breakpoint_thread_switch(struct task_struct *next) /* * CPU initialisation. */ -static void reset_ctrl_regs(void *unused) +static void hw_breakpoint_reset(void *unused) { int i; - - for (i = 0; i < core_num_brps; ++i) { - write_wb_reg(AARCH64_DBG_REG_BCR, i, 0UL); - write_wb_reg(AARCH64_DBG_REG_BVR, i, 0UL); + struct perf_event **slots; + /* + * When a CPU goes through cold-boot, it does not have any installed + * slot, so it is safe to share the same function for restoring and + * resetting breakpoints; when a CPU is hotplugged in, it goes + * through the slots, which are all empty, hence it just resets control + * and value for debug registers. + * When this function is triggered on warm-boot through a CPU PM + * notifier some slots might be initialized; if so they are + * reprogrammed according to the debug slots content. + */ + for (slots = this_cpu_ptr(bp_on_reg), i = 0; i < core_num_brps; ++i) { + if (slots[i]) { + hw_breakpoint_control(slots[i], HW_BREAKPOINT_RESTORE); + } else { + write_wb_reg(AARCH64_DBG_REG_BCR, i, 0UL); + write_wb_reg(AARCH64_DBG_REG_BVR, i, 0UL); + }
When this runs on warm-boot and starts restoring debug state, are debug exceptions guaranteed to be masked? I think that the debug restoration should appear atomic to a debugger (i.e. you can't take a debug exception half-way through the restore). Providing that's the case: Acked-by: Will Deacon [off-list ref] Will