[PATCH v4 2/9] riscv: smp: fail booting up smp if inconsistent vlen is detected

[Andy Chiu]

On Thu, Apr 25, 2024 at 4:01 AM Alexandre Ghiti <alex at ghiti.fr> wrote:
>
> Hi Andy,
>
> On 12/04/2024 08:48, Andy Chiu wrote:
> > Currently we only support Vector for SMP platforms, that is, all SMP
> > cores have the same vlenb. If we happen to detect a mismatching vlen, it
> > is better to just fail bootting it up to prevent further race/scheduling
> > issues.
> >
> > Also, move .Lsecondary_park forward and chage `tail smp_callin` into a
> > regular call in the early assembly. So a core would be parked right
> > after a return from smp_callin. Note that a successful smp_callin
> > does not return.
> >
> > Fixes: 7017858eb2d7 ("riscv: Introduce riscv_v_vsize to record size of Vector context")
> > Reported-by: Conor Dooley <conor.dooley at microchip.com>
> > Closes: https://lore.kernel.org/linux-riscv/20240228-vicinity-cornstalk-4b8eb5fe5730@spud/
> > Signed-off-by: Andy Chiu <andy.chiu at sifive.com>
> > ---
> > Changelog v4:
> >   - update comment also in the assembly code (Yunhui)
> > Changelog v2:
> >   - update commit message to explain asm code change (Conor)
> > ---
> >   arch/riscv/kernel/head.S    | 19 ++++++++++++-------
> >   arch/riscv/kernel/smpboot.c | 14 +++++++++-----
> >   2 files changed, 21 insertions(+), 12 deletions(-)
> >
> > diff --git a/arch/riscv/kernel/head.S b/arch/riscv/kernel/head.S
> > index 4236a69c35cb..a00f7523cb91 100644
> > --- a/arch/riscv/kernel/head.S
> > +++ b/arch/riscv/kernel/head.S
> > @@ -165,9 +165,20 @@ secondary_start_sbi:
> >   #endif
> >       call .Lsetup_trap_vector
> >       scs_load_current
> > -     tail smp_callin
> > +     call smp_callin
> >   #endif /* CONFIG_SMP */
> >
> > +.align 2
> > +.Lsecondary_park:
> > +     /*
> > +      * Park this hart if we:
> > +      *  - have too many harts on CONFIG_RISCV_BOOT_SPINWAIT
> > +      *  - receive an early trap, before setup_trap_vector finished
> > +      *  - fail in smp_callin(), as a successful one wouldn't return
> > +      */
> > +     wfi
> > +     j .Lsecondary_park
> > +
> >   .align 2
> >   .Lsetup_trap_vector:
> >       /* Set trap vector to exception handler */
> > @@ -181,12 +192,6 @@ secondary_start_sbi:
> >       csrw CSR_SCRATCH, zero
> >       ret
> >
> > -.align 2
> > -.Lsecondary_park:
> > -     /* We lack SMP support or have too many harts, so park this hart */
> > -     wfi
> > -     j .Lsecondary_park
> > -
> >   SYM_CODE_END(_start)
> >
> >   SYM_CODE_START(_start_kernel)
> > diff --git a/arch/riscv/kernel/smpboot.c b/arch/riscv/kernel/smpboot.c
> > index d41090fc3203..673437ccc13d 100644
> > --- a/arch/riscv/kernel/smpboot.c
> > +++ b/arch/riscv/kernel/smpboot.c
> > @@ -214,6 +214,15 @@ asmlinkage __visible void smp_callin(void)
> >       struct mm_struct *mm = &init_mm;
> >       unsigned int curr_cpuid = smp_processor_id();
> >
> > +     if (has_vector()) {
> > +             /*
> > +              * Return as early as possible so the hart with a mismatching
> > +              * vlen won't boot.
> > +              */
> > +             if (riscv_v_setup_vsize())
> > +                     return;
> > +     }
> > +
> >       /* All kernel threads share the same mm context.  */
> >       mmgrab(mm);
> >       current->active_mm = mm;
> > @@ -226,11 +235,6 @@ asmlinkage __visible void smp_callin(void)
> >       numa_add_cpu(curr_cpuid);
> >       set_cpu_online(curr_cpuid, 1);
> >
> > -     if (has_vector()) {
> > -             if (riscv_v_setup_vsize())
> > -                     elf_hwcap &= ~COMPAT_HWCAP_ISA_V;
> > -     }
> > -
> >       riscv_user_isa_enable();
> >
> >       /*
> >
>
> So this should go into -fixes, would you mind sending a single patch for
> this fix?

I thought it would be magically picked up by a bot as long as we have
a fix tag. Am I assuming something wrong?

>
> Your patch 8 is actually already fixed by Clement's patch
> https://lore.kernel.org/linux-riscv/20240409143839.558784-1-cleger@rivosinc.com/

Okay, I will drop it at the next revision.

> and I already mentioned this one to Palmer.
>
> Thanks,
>
> Alex
>

Thanks,
Andy