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Message-ID: <CAAhSdy2BqJseXoNRQJ7d69ExDFu=DfRW-Q_inZoDcPzAWDTToQ@mail.gmail.com>
Date: Mon, 13 Dec 2021 18:20:52 +0530
From: Anup Patel <anup@...infault.org>
To: Atish Patra <atishp@...shpatra.org>
Cc: "linux-kernel@...r.kernel.org List" <linux-kernel@...r.kernel.org>,
Atish Patra <atishp@...osinc.com>,
Alexandre Ghiti <alex@...ti.fr>,
Anup Patel <anup.patel@....com>,
Greentime Hu <greentime.hu@...ive.com>,
Guo Ren <guoren@...ux.alibaba.com>,
Heinrich Schuchardt <xypron.glpk@....de>,
Ingo Molnar <mingo@...nel.org>,
Jisheng Zhang <jszhang@...nel.org>,
kvm-riscv@...ts.infradead.org, KVM General <kvm@...r.kernel.org>,
linux-riscv <linux-riscv@...ts.infradead.org>,
Marc Zyngier <maz@...nel.org>,
Nanyong Sun <sunnanyong@...wei.com>,
Nick Kossifidis <mick@....forth.gr>,
Palmer Dabbelt <palmer@...belt.com>,
Paul Walmsley <paul.walmsley@...ive.com>,
Pekka Enberg <penberg@...nel.org>,
Vincent Chen <vincent.chen@...ive.com>,
Vitaly Wool <vitaly.wool@...sulko.com>
Subject: Re: [RFC 3/6] RISC-V: Use __cpu_up_stack/task_pointer only for
spinwait method
On Sat, Dec 4, 2021 at 5:51 AM Atish Patra <atishp@...shpatra.org> wrote:
>
> From: Atish Patra <atishp@...osinc.com>
>
> The __cpu_up_stack/task_pointer array is only used for spinwait method
> now. The per cpu array based lookup is also fragile for platforms with
> discontiguous/sparse hartids. The spinwait method is only used for
> M-mode Linux or older firmwares without SBI HSM extension. For general
> Linux systems, ordered booting method is preferred anyways to support
> cpu hotplug and kexec.
>
> Make sure that __cpu_up_stack/task_pointer is only used for spinwait
> method. Take this opportunity to rename it to
> __cpu_spinwait_stack/task_pointer to emphasize the purpose as well.
>
> Signed-off-by: Atish Patra <atishp@...osinc.com>
Looks good to me.
Reviewed-by: Anup Patel <anup@...infault.org>
Regards,
Anup
> ---
> arch/riscv/include/asm/cpu_ops.h | 2 --
> arch/riscv/kernel/cpu_ops.c | 16 ----------------
> arch/riscv/kernel/cpu_ops_spinwait.c | 27 ++++++++++++++++++++++++++-
> arch/riscv/kernel/head.S | 4 ++--
> arch/riscv/kernel/head.h | 4 ++--
> 5 files changed, 30 insertions(+), 23 deletions(-)
>
> diff --git a/arch/riscv/include/asm/cpu_ops.h b/arch/riscv/include/asm/cpu_ops.h
> index a8ec3c5c1bd2..134590f1b843 100644
> --- a/arch/riscv/include/asm/cpu_ops.h
> +++ b/arch/riscv/include/asm/cpu_ops.h
> @@ -40,7 +40,5 @@ struct cpu_operations {
>
> extern const struct cpu_operations *cpu_ops[NR_CPUS];
> void __init cpu_set_ops(int cpu);
> -void cpu_update_secondary_bootdata(unsigned int cpuid,
> - struct task_struct *tidle);
>
> #endif /* ifndef __ASM_CPU_OPS_H */
> diff --git a/arch/riscv/kernel/cpu_ops.c b/arch/riscv/kernel/cpu_ops.c
> index 3f5a38b03044..c1e30f403c3b 100644
> --- a/arch/riscv/kernel/cpu_ops.c
> +++ b/arch/riscv/kernel/cpu_ops.c
> @@ -8,31 +8,15 @@
> #include <linux/of.h>
> #include <linux/string.h>
> #include <linux/sched.h>
> -#include <linux/sched/task_stack.h>
> #include <asm/cpu_ops.h>
> #include <asm/sbi.h>
> #include <asm/smp.h>
>
> const struct cpu_operations *cpu_ops[NR_CPUS] __ro_after_init;
>
> -void *__cpu_up_stack_pointer[NR_CPUS] __section(".data");
> -void *__cpu_up_task_pointer[NR_CPUS] __section(".data");
> -
> extern const struct cpu_operations cpu_ops_sbi;
> extern const struct cpu_operations cpu_ops_spinwait;
>
> -void cpu_update_secondary_bootdata(unsigned int cpuid,
> - struct task_struct *tidle)
> -{
> - int hartid = cpuid_to_hartid_map(cpuid);
> -
> - /* Make sure tidle is updated */
> - smp_mb();
> - WRITE_ONCE(__cpu_up_stack_pointer[hartid],
> - task_stack_page(tidle) + THREAD_SIZE);
> - WRITE_ONCE(__cpu_up_task_pointer[hartid], tidle);
> -}
> -
> void __init cpu_set_ops(int cpuid)
> {
> #if IS_ENABLED(CONFIG_RISCV_SBI)
> diff --git a/arch/riscv/kernel/cpu_ops_spinwait.c b/arch/riscv/kernel/cpu_ops_spinwait.c
> index b2c957bb68c1..9f398eb94f7a 100644
> --- a/arch/riscv/kernel/cpu_ops_spinwait.c
> +++ b/arch/riscv/kernel/cpu_ops_spinwait.c
> @@ -6,11 +6,36 @@
> #include <linux/errno.h>
> #include <linux/of.h>
> #include <linux/string.h>
> +#include <linux/sched/task_stack.h>
> #include <asm/cpu_ops.h>
> #include <asm/sbi.h>
> #include <asm/smp.h>
>
> const struct cpu_operations cpu_ops_spinwait;
> +void *__cpu_spinwait_stack_pointer[NR_CPUS] __section(".data");
> +void *__cpu_spinwait_task_pointer[NR_CPUS] __section(".data");
> +
> +static void cpu_update_secondary_bootdata(unsigned int cpuid,
> + struct task_struct *tidle)
> +{
> + int hartid = cpuid_to_hartid_map(cpuid);
> +
> + /*
> + * The hartid must be less than NR_CPUS to avoid out-of-bound access
> + * errors for __cpu_spinwait_stack/task_pointer. That is not always possible
> + * for platforms with discontiguous hartid numbering scheme. That's why
> + * spinwait booting is not the recommended approach for any platforms
> + * and will be removed in future.
> + */
> + if (hartid == INVALID_HARTID || hartid >= NR_CPUS)
> + return;
> +
> + /* Make sure tidle is updated */
> + smp_mb();
> + WRITE_ONCE(__cpu_spinwait_stack_pointer[hartid],
> + task_stack_page(tidle) + THREAD_SIZE);
> + WRITE_ONCE(__cpu_spinwait_task_pointer[hartid], tidle);
> +}
>
> static int spinwait_cpu_prepare(unsigned int cpuid)
> {
> @@ -28,7 +53,7 @@ static int spinwait_cpu_start(unsigned int cpuid, struct task_struct *tidle)
> * selects the first cpu to boot the kernel and causes the remainder
> * of the cpus to spin in a loop waiting for their stack pointer to be
> * setup by that main cpu. Writing to bootdata
> - * (i.e __cpu_up_stack_pointer) signals to the spinning cpus that they
> + * (i.e __cpu_spinwait_stack_pointer) signals to the spinning cpus that they
> * can continue the boot process.
> */
> cpu_update_secondary_bootdata(cpuid, tidle);
> diff --git a/arch/riscv/kernel/head.S b/arch/riscv/kernel/head.S
> index 40d4c625513c..6f8e99eac6a1 100644
> --- a/arch/riscv/kernel/head.S
> +++ b/arch/riscv/kernel/head.S
> @@ -347,9 +347,9 @@ clear_bss_done:
> csrw CSR_TVEC, a3
>
> slli a3, a0, LGREG
> - la a1, __cpu_up_stack_pointer
> + la a1, __cpu_spinwait_stack_pointer
> XIP_FIXUP_OFFSET a1
> - la a2, __cpu_up_task_pointer
> + la a2, __cpu_spinwait_task_pointer
> XIP_FIXUP_OFFSET a2
> add a1, a3, a1
> add a2, a3, a2
> diff --git a/arch/riscv/kernel/head.h b/arch/riscv/kernel/head.h
> index aabbc3ac3e48..5393cca77790 100644
> --- a/arch/riscv/kernel/head.h
> +++ b/arch/riscv/kernel/head.h
> @@ -16,7 +16,7 @@ asmlinkage void __init setup_vm(uintptr_t dtb_pa);
> asmlinkage void __init __copy_data(void);
> #endif
>
> -extern void *__cpu_up_stack_pointer[];
> -extern void *__cpu_up_task_pointer[];
> +extern void *__cpu_spinwait_stack_pointer[];
> +extern void *__cpu_spinwait_task_pointer[];
>
> #endif /* __ASM_HEAD_H */
> --
> 2.33.1
>
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