Re: [PATCH v2 3/6] RISC-V: Check scalar unaligned access on all CPUs

Charlie Jenkins
2024-06-17T23:57:20Z

On Fri, Jun 14, 2024 at 09:22:47AM +0100, Conor Dooley wrote:
> On Thu, Jun 13, 2024 at 03:16:12PM -0400, Jesse Taube wrote:
> > Originally, the check_unaligned_access_emulated_all_cpus function
> > only checked the boot hart. This fixes the function to check all
> > harts.
>
> This seems like it should be split out and get a Fixes: tag & a cc:
> stable.

These changes are great Jesse! I agree with Conor, please split these
changes into two different patches with a fixes tag for
71c54b3d169d ("riscv: report misaligned accesses emulation to hwprobe").

- Charlie

>
> > Check for Zicclsm before checking for unaligned access. This will
> > greatly reduce the boot up time as finding the access speed is no longer
> > necessary.
> >
> > Signed-off-by: Jesse Taube <jesse@rivosinc.com>
> > ---
> > V1 -> V2:
> > - New patch
> > ---
> > arch/riscv/kernel/traps_misaligned.c | 23 ++++++----------------
> > arch/riscv/kernel/unaligned_access_speed.c | 23 +++++++++++++---------
> > 2 files changed, 20 insertions(+), 26 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();
> > - }
> > -
> > - 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;
> > diff --git a/arch/riscv/kernel/unaligned_access_speed.c b/arch/riscv/kernel/unaligned_access_speed.c
> > index a9a6bcb02acf..70c1588fc353 100644
> > --- a/arch/riscv/kernel/unaligned_access_speed.c
> > +++ b/arch/riscv/kernel/unaligned_access_speed.c
> > @@ -259,23 +259,28 @@ static int check_unaligned_access_speed_all_cpus(void)
> > kfree(bufs);
> > return 0;
> > }
> > +#endif /* CONFIG_RISCV_PROBE_UNALIGNED_ACCESS */
> >
> > static int check_unaligned_access_all_cpus(void)
> > {
> > - bool all_cpus_emulated = check_unaligned_access_emulated_all_cpus();
> > + bool all_cpus_emulated;
> > + int cpu;
> >
> > + if (riscv_has_extension_unlikely(RISCV_ISA_EXT_ZICCLSM)) {
> > + for_each_online_cpu(cpu) {
> > + per_cpu(misaligned_access_speed, cpu) = RISCV_HWPROBE_MISALIGNED_FAST;
> > + }
> > + return 0;
> > + }
> > +
> > + all_cpus_emulated = check_unaligned_access_emulated_all_cpus();
> > +
> > +#ifdef CONFIG_RISCV_PROBE_UNALIGNED_ACCESS
>
> Can we make this an IS_ENABLED() please?
>
>
> Thanks,
> Conor.
>
> > if (!all_cpus_emulated)
> > return check_unaligned_access_speed_all_cpus();
> > +#endif
> >
> > return 0;
> > }
> > -#else /* CONFIG_RISCV_PROBE_UNALIGNED_ACCESS */
> > -static int check_unaligned_access_all_cpus(void)
> > -{
> > - check_unaligned_access_emulated_all_cpus();
> > -
> > - return 0;
> > -}
> > -#endif
> >
> > arch_initcall(check_unaligned_access_all_cpus);
> > --
> > 2.43.0
> >