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Message-ID: <c0b15ad6-4385-41bb-82a6-a43107c0e0a1.guoren@linux.alibaba.com>
Date: Sat, 27 Jun 2020 00:28:38 +0800
From: "guoren" <guoren@...ux.alibaba.com>
To: "Greentime Hu" <greentime.hu@...ive.com>,
"linux-riscv" <linux-riscv@...ts.infradead.org>,
"linux-kernel" <linux-kernel@...r.kernel.org>,
"aou" <aou@...s.berkeley.edu>, "palmer" <palmer@...belt.com>,
"paul.walmsley" <paul.walmsley@...ive.com>,
"guoren" <guoren@...ux.alibaba.com>
Subject: Re: [PATCH 2/2] riscv: Enable context tracking
Hi Greentime,
On 2020/6/23 9:28 下午, Greentime Hu wrote:
> This patch implements and enables context tracking for riscv (which is a
> prerequisite for CONFIG_NO_HZ_FULL support)
>
> It adds checking for previous state in the entry that all excepttions and
> interrupts goes to and calls context_tracking_user_exit() if it comes from
> user space. It also calls context_tracking_user_enter() if it will return
> to user space before restore_all.
>
> This patch is tested with the dynticks-testing testcase in
> qemu-system-riscv64 virt machine and Unleashed board.
> git://git.kernel.org/pub/scm/linux/kernel/git/frederic/dynticks-testing.git
>
> We can see the log here. The tick got mostly stopped during the execution
> of the user loop.
>
> _-----=> irqs-off
> / _----=> need-resched
> | / _---=> hardirq/softirq
> || / _--=> preempt-depth
> ||| / delay
> TASK-PID CPU# |||| TIMESTAMP FUNCTION
> | | | |||| | |
> <idle>-0 [001] d..2 604.183512: sched_switch: prev_comm=swapper/1 prev_pid=0 prev_prio=120 prev_state=R ==> next_comm=taskset next_pid=273 next_prio=120
> user_loop-273 [001] d.h1 604.184788: hrtimer_expire_entry: hrtimer=000000002eda5fab function=tick_sched_timer now=604176096300
> user_loop-273 [001] d.s2 604.184897: workqueue_queue_work: work struct=00000000383402c2 function=vmstat_update workqueue=00000000f36d35d4 req_cpu=1 cpu=1
> user_loop-273 [001] dns2 604.185039: tick_stop: success=0 dependency=SCHED
> user_loop-273 [001] dn.1 604.185103: tick_stop: success=0 dependency=SCHED
> user_loop-273 [001] d..2 604.185154: sched_switch: prev_comm=taskset prev_pid=273 prev_prio=120 prev_state=R+ ==> next_comm=kworker/1:1 next_pid=46 next_prio=120
> <...>-46 [001] .... 604.185194: workqueue_execute_start: work struct 00000000383402c2: function vmstat_update
> <...>-46 [001] d..2 604.185266: sched_switch: prev_comm=kworker/1:1 prev_pid=46 prev_prio=120 prev_state=I ==> next_comm=taskset next_pid=273 next_prio=120
> user_loop-273 [001] d.h1 604.188812: hrtimer_expire_entry: hrtimer=000000002eda5fab function=tick_sched_timer now=604180133400
> user_loop-273 [001] d..1 604.189050: tick_stop: success=1 dependency=NONE
> user_loop-273 [001] d..2 614.251386: sched_switch: prev_comm=user_loop prev_pid=273 prev_prio=120 prev_state=X ==> next_comm=swapper/1 next_pid=0 next_prio=120
> <idle>-0 [001] d..2 614.315391: sched_switch: prev_comm=swapper/1 prev_pid=0 prev_prio=120 prev_state=R ==> next_comm=taskset next_pid=276 next_prio=120
>
> Signed-off-by: Greentime Hu<greentime.hu@...ive.com>
> ---
> arch/riscv/Kconfig | 1 +
> arch/riscv/kernel/entry.S | 23 +++++++++++++++++++++++
> 2 files changed, 24 insertions(+)
>
> diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
> index 128192e14ff2..17520e11815b 100644
> --- a/arch/riscv/Kconfig
> +++ b/arch/riscv/Kconfig
> @@ -52,6 +52,7 @@ config RISCV
> select HAVE_ARCH_SECCOMP_FILTER
> select HAVE_ARCH_TRACEHOOK
> select HAVE_ASM_MODVERSIONS
> + select HAVE_CONTEXT_TRACKING
> select HAVE_COPY_THREAD_TLS
> select HAVE_DMA_CONTIGUOUS if MMU
> select HAVE_EBPF_JIT if MMU
> diff --git a/arch/riscv/kernel/entry.S b/arch/riscv/kernel/entry.S
> index cae7e6d4c7ef..6ed579fc1073 100644
> --- a/arch/riscv/kernel/entry.S
> +++ b/arch/riscv/kernel/entry.S
> @@ -97,6 +97,14 @@ _save_context:
> la gp, __global_pointer$
> .option pop
>
> +#ifdef CONFIG_CONTEXT_TRACKING
> + /* If previous state is in user mode, call context_tracking_user_exit. */
> + andi a0, s1, SR_SPP
> + bnez a0, skip_context_tracking
> + call context_tracking_user_exit
It will destroy s1-s5 which are used in entry.S like these:
REG_S s0, PT_SP(sp)
REG_S s1, PT_STATUS(sp)
REG_S s2, PT_EPC(sp)
REG_S s3, PT_BADADDR(sp)
REG_S s4, PT_CAUSE(sp)
REG_S s5, PT_TP(sp)
...
/*
* MSB of cause differentiates between
* interrupts and exceptions
*/
bge s4, zero, 1f
...
/*
* Exceptions run with interrupts enabled or disabled depending
on the
* state of SR_PIE in m/sstatus.
*/
andi t0, s1, SR_PIE
...
/* Handle syscalls */
li t0, EXC_SYSCALL
beq s4, t0, handle_syscall
...
I also solved it in my lockdep patches, please have a look:
https://lore.kernel.org/linux-riscv/1592323021-98541-4-git-send-email-guoren@kernel.org/T/#u
Best Regards
Guo Ren
> +
> +skip_context_tracking:
> +#endif
> la ra, ret_from_exception
> /*
> * MSB of cause differentiates between
> @@ -137,6 +145,17 @@ _save_context:
> tail do_trap_unknown
>
> handle_syscall:
> +#ifdef CONFIG_CONTEXT_TRACKING
> + /* Recover a0 - a7 for system calls */
> + REG_L x10, PT_A0(sp)
> + REG_L x11, PT_A1(sp)
> + REG_L x12, PT_A2(sp)
> + REG_L x13, PT_A3(sp)
> + REG_L x14, PT_A4(sp)
> + REG_L x15, PT_A5(sp)
> + REG_L x16, PT_A6(sp)
> + REG_L x17, PT_A7(sp)
> +#endif
> /* save the initial A0 value (needed in signal handlers) */
> REG_S a0, PT_ORIG_A0(sp)
> /*
> @@ -205,6 +224,10 @@ resume_userspace:
> andi s1, s0, _TIF_WORK_MASK
> bnez s1, work_pending
>
> +#ifdef CONFIG_CONTEXT_TRACKING
> + call context_tracking_user_enter
> +#endif
> +
> /* Save unwound kernel stack pointer in thread_info */
> addi s0, sp, PT_SIZE_ON_STACK
> REG_S s0, TASK_TI_KERNEL_SP(tp)
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