Re: [PATCH v8 09/11] RISC-V: Add supported for ordered booting method using HSM

[Anup Patel <anup@brainfault.org>]

On Wed, Feb 12, 2020 at 7:21 AM Atish Patra <atish.patra@wdc.com> wrote:
>
> Currently, all harts have to jump Linux in RISC-V. This complicates the
> multi-stage boot process as every transient stage also has to ensure all
> harts enter to that stage and jump to Linux afterwards. It also obstructs
> a clean Kexec implementation.
>
> SBI HSM extension provides alternate solutions where only a single hart
> need to boot and enter Linux. The booting hart can bring up secondary
> harts one by one afterwards.
>
> Add SBI HSM based cpu_ops that implements an ordered booting method in
> RISC-V. This change is also backward compatible with older firmware not
> implementing HSM extension. If a latest kernel is used with older
> firmware, it will continue to use the default spinning booting method.
>
> Signed-off-by: Atish Patra <atish.patra@wdc.com>
> ---
>  arch/riscv/kernel/cpu_ops.c     | 10 +++++++++-
>  arch/riscv/kernel/cpu_ops_sbi.c | 31 +++++++++++++++++++++++++++++++
>  arch/riscv/kernel/head.S        | 26 ++++++++++++++++++++++++++
>  arch/riscv/kernel/smpboot.c     |  2 +-
>  arch/riscv/kernel/traps.c       |  2 +-
>  5 files changed, 68 insertions(+), 3 deletions(-)
>
> diff --git a/arch/riscv/kernel/cpu_ops.c b/arch/riscv/kernel/cpu_ops.c
> index 1085def3735a..6221bbedaea4 100644
> --- a/arch/riscv/kernel/cpu_ops.c
> +++ b/arch/riscv/kernel/cpu_ops.c
> @@ -18,6 +18,7 @@ const struct cpu_operations *cpu_ops[NR_CPUS] __ro_after_init;
>  void *__cpu_up_stack_pointer[NR_CPUS];
>  void *__cpu_up_task_pointer[NR_CPUS];
>
> +extern const struct cpu_operations cpu_ops_sbi;
>  extern const struct cpu_operations cpu_ops_spinwait;
>
>  void cpu_update_secondary_bootdata(unsigned int cpuid,
> @@ -34,7 +35,14 @@ void cpu_update_secondary_bootdata(unsigned int cpuid,
>
>  int __init cpu_set_ops(int cpuid)
>  {
> -       cpu_ops[cpuid] = &cpu_ops_spinwait;
> +#if IS_ENABLED(CONFIG_RISCV_SBI)
> +       if (sbi_probe_extension(SBI_EXT_HSM) > 0) {
> +               if (!cpuid)
> +                       pr_info("SBI v0.2 HSM extension detected\n");
> +               cpu_ops[cpuid] = &cpu_ops_sbi;
> +       } else
> +#endif
> +               cpu_ops[cpuid] = &cpu_ops_spinwait;
>
>         return 0;
>  }
> diff --git a/arch/riscv/kernel/cpu_ops_sbi.c b/arch/riscv/kernel/cpu_ops_sbi.c
> index 9bdb60e0a4df..31487a80c3b8 100644
> --- a/arch/riscv/kernel/cpu_ops_sbi.c
> +++ b/arch/riscv/kernel/cpu_ops_sbi.c
> @@ -7,9 +7,13 @@
>
>  #include <linux/init.h>
>  #include <linux/mm.h>
> +#include <asm/cpu_ops.h>
>  #include <asm/sbi.h>
>  #include <asm/smp.h>
>
> +extern char secondary_start_sbi[];
> +const struct cpu_operations cpu_ops_sbi;
> +
>  static int sbi_hsm_hart_stop(void)
>  {
>         struct sbiret ret;
> @@ -46,3 +50,30 @@ static int sbi_hsm_hart_get_status(unsigned long hartid)
>         else
>                 return ret.value;
>  }
> +
> +static int sbi_cpu_start(unsigned int cpuid, struct task_struct *tidle)
> +{
> +       int rc;
> +       unsigned long boot_addr = __pa_symbol(secondary_start_sbi);
> +       int hartid = cpuid_to_hartid_map(cpuid);
> +
> +       cpu_update_secondary_bootdata(cpuid, tidle);
> +       rc = sbi_hsm_hart_start(hartid, boot_addr, 0);
> +
> +       return rc;
> +}
> +
> +static int sbi_cpu_prepare(unsigned int cpuid)
> +{
> +       if (!cpu_ops_sbi.cpu_start) {
> +               pr_err("cpu start method not defined for CPU [%d]\n", cpuid);
> +               return -ENODEV;
> +       }
> +       return 0;
> +}
> +
> +const struct cpu_operations cpu_ops_sbi = {
> +       .name           = "sbi",
> +       .cpu_prepare    = sbi_cpu_prepare,
> +       .cpu_start      = sbi_cpu_start,
> +};
> diff --git a/arch/riscv/kernel/head.S b/arch/riscv/kernel/head.S
> index c1be597d22a1..8386cfafba98 100644
> --- a/arch/riscv/kernel/head.S
> +++ b/arch/riscv/kernel/head.S
> @@ -99,11 +99,37 @@ relocate:
>         ret
>  #endif /* CONFIG_MMU */
>  #ifdef CONFIG_SMP
> +       .global secondary_start_sbi
> +secondary_start_sbi:
> +       /* Mask all interrupts */
> +       csrw CSR_IE, zero
> +       csrw CSR_IP, zero
> +
> +       /* Load the global pointer */
> +       .option push
> +       .option norelax
> +               la gp, __global_pointer$
> +       .option pop
> +
> +       /*
> +        * Disable FPU to detect illegal usage of
> +        * floating point in kernel space
> +        */
> +       li t0, SR_FS
> +       csrc CSR_STATUS, t0
> +
>         /* Set trap vector to spin forever to help debug */
>         la a3, .Lsecondary_park
>         csrw CSR_TVEC, a3
>
>         slli a3, a0, LGREG
> +       la a4, __cpu_up_stack_pointer
> +       la a5, __cpu_up_task_pointer
> +       add a4, a3, a4
> +       add a5, a3, a5
> +       REG_L sp, (a4)
> +       REG_L tp, (a5)
> +
>         .global secondary_start_common
>  secondary_start_common:
>
> diff --git a/arch/riscv/kernel/smpboot.c b/arch/riscv/kernel/smpboot.c
> index 2ee41c779a16..2c56ac70e64d 100644
> --- a/arch/riscv/kernel/smpboot.c
> +++ b/arch/riscv/kernel/smpboot.c
> @@ -146,7 +146,7 @@ void __init smp_cpus_done(unsigned int max_cpus)
>  /*
>   * C entry point for a secondary processor.
>   */
> -asmlinkage __visible void __init smp_callin(void)
> +asmlinkage __visible void smp_callin(void)
>  {
>         struct mm_struct *mm = &init_mm;
>
> diff --git a/arch/riscv/kernel/traps.c b/arch/riscv/kernel/traps.c
> index f4cad5163bf2..0063dd7318d6 100644
> --- a/arch/riscv/kernel/traps.c
> +++ b/arch/riscv/kernel/traps.c
> @@ -147,7 +147,7 @@ int is_valid_bugaddr(unsigned long pc)
>  }
>  #endif /* CONFIG_GENERIC_BUG */
>
> -void __init trap_init(void)
> +void trap_init(void)
>  {
>         /*
>          * Set sup0 scratch register to 0, indicating to exception vector
> --
> 2.24.0
>

Overall, this patch looks good but SBI HSM helper functions
from PATCH8 should be moved to this patch.

Reviewed-by: Anup Patel <anup@brainfault.org>

Regards,
Anup