Re: [PATCH v3 3/8] RISC-V: Check scalar unaligned access on all CPUs

[Jesse Taube]

On 7/10/24 11:55, Evan Green wrote:
> On Mon, Jun 24, 2024 at 5:51 PM Jesse Taube <jesse@xxxxxxxxxxxx> wrote:
> > Originally, the check_unaligned_access_emulated_all_cpus function
> > only checked the boot hart. This fixes the function to check all
> > harts.
> >
> > Fixes: 71c54b3d169d ("riscv: report misaligned accesses emulation to hwprobe")
> > Signed-off-by: Jesse Taube <jesse@xxxxxxxxxxxx>
> > Cc: stable@xxxxxxxxxxxxxxx
> > ---
> > V1 -> V2:
> >   - New patch
> > V2 -> V3:
> >   - Split patch
> > ---
> >   arch/riscv/kernel/traps_misaligned.c | 23 ++++++-----------------
> >   1 file changed, 6 insertions(+), 17 deletions(-)
> >
> > diff --git a/arch/riscv/kernel/traps_misaligned.c b/arch/riscv/kernel/traps_misaligned.c
> > index b62d5a2f4541..8fadbe00dd62 100644
> > --- a/arch/riscv/kernel/traps_misaligned.c
> > +++ b/arch/riscv/kernel/traps_misaligned.c
> > @@ -526,31 +526,17 @@ int handle_misaligned_store(struct pt_regs *regs)
> >          return 0;
> >   }
> >
> > -static bool check_unaligned_access_emulated(int cpu)
> > +static void check_unaligned_access_emulated(struct work_struct *unused)
> >   {
> > +       int cpu = smp_processor_id();
> >          long *mas_ptr = per_cpu_ptr(&misaligned_access_speed, cpu);
> >          unsigned long tmp_var, tmp_val;
> > -       bool misaligned_emu_detected;
> >
> >          *mas_ptr = RISCV_HWPROBE_MISALIGNED_UNKNOWN;
> >
> >          __asm__ __volatile__ (
> >                  "       "REG_L" %[tmp], 1(%[ptr])\n"
> >                  : [tmp] "=r" (tmp_val) : [ptr] "r" (&tmp_var) : "memory");
> > -
> > -       misaligned_emu_detected = (*mas_ptr == RISCV_HWPROBE_MISALIGNED_EMULATED);
> > -       /*
> > -        * If unaligned_ctl is already set, this means that we detected that all
> > -        * CPUS uses emulated misaligned access at boot time. If that changed
> > -        * when hotplugging the new cpu, this is something we don't handle.
> > -        */
> > -       if (unlikely(unaligned_ctl && !misaligned_emu_detected)) {
> > -               pr_crit("CPU misaligned accesses non homogeneous (expected all emulated)\n");
> > -               while (true)
> > -                       cpu_relax();
> > -       }
>
> This chunk was meant to detect and refuse to run on a system where a
> heterogeneous CPU is hotplugged into a previously homogenous system.
> The commit message doesn't mention this change, how come you
> deleted it?

Sorry for the long wait.
I do not remember why I removed this.
Your right it shouldn't be removed, I added it back.

Thanks,
Jesse Taube
> > -
> > -       return misaligned_emu_detected;
> >   }
> >
> >   bool check_unaligned_access_emulated_all_cpus(void)
> > @@ -562,8 +548,11 @@ bool check_unaligned_access_emulated_all_cpus(void)
> >           * accesses emulated since tasks requesting such control can run on any
> >           * CPU.
> >           */
> > +       schedule_on_each_cpu(check_unaligned_access_emulated);
> > +
> >          for_each_online_cpu(cpu)
> > -               if (!check_unaligned_access_emulated(cpu))
> > +               if (per_cpu(misaligned_access_speed, cpu)
> > +                   != RISCV_HWPROBE_MISALIGNED_EMULATED)
> >                          return false;
> >
> >          unaligned_ctl = true;
> > --
> > 2.45.2