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Message-ID: <CAHCEeh+8wzxLGEU7Mr18j6bTzYCG8fUtHBAKv6AJ7ZnEkjNr=w@mail.gmail.com>
Date: Sat, 11 Jul 2020 09:47:33 +0800
From: Greentime Hu <greentime.hu@...ive.com>
To: Palmer Dabbelt <palmer@...belt.com>
Cc: linux-riscv <linux-riscv@...ts.infradead.org>,
Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
Albert Ou <aou@...s.berkeley.edu>,
Paul Walmsley <paul.walmsley@...ive.com>,
Guo Ren <guoren@...ux.alibaba.com>
Subject: Re: [PATCH v2 2/2] riscv: Enable context tracking
Palmer Dabbelt <palmer@...belt.com> 於 2020年7月11日 週六 上午1:30寫道：
>
> On Wed, 24 Jun 2020 02:03:16 PDT (-0700), greentime.hu@...ive.com 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
>
> I've changed that to SR_PP, as I don't see any reason why this should depend on
> MMU.
>
> I think this is correct: we're using scratch==0 elsewhere to detect recursive
> traps, but we've blown that away by this point so it's not an option. I don't
> know of any reason why PP wouldn't be accurate.
Hi Palmer,
Thank you. That makes sense to me.
>
> > + bnez a0, skip_context_tracking
> > + call context_tracking_user_exit
> > +
> > +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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