Re: [PATCH] riscv: Ensure isa-ext static keys are writable

[Palmer Dabbelt]

On Tue, 16 Aug 2022 16:41:46 PDT (-0700), atishp@xxxxxxxxxxxxxx wrote:
> On Tue, Aug 16, 2022 at 9:31 AM Andrew Jones <ajones@xxxxxxxxxxxxxxxx> wrote:
> > riscv_isa_ext_keys[] is an array of static keys used in the unified
> > ISA extension framework. The keys added to this array may be used
> > anywhere, including in modules. Ensure the keys remain writable by
> > placing them in the data section.
> >
> > The need to change riscv_isa_ext_keys[]'s section was found when the
> > kvm module started failing to load. Commit 8eb060e10185 ("arch/riscv:
> > add Zihintpause support") adds a static branch check for a newly
> > added isa-ext key to cpu_relax(), which kvm uses.
> >
> > Fixes: c360cbec3511 ("riscv: introduce unified static key mechanism for ISA extensions")
> > Signed-off-by: Andrew Jones <ajones@xxxxxxxxxxxxxxxx>
> > ---
> >  arch/riscv/kernel/cpufeature.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/arch/riscv/kernel/cpufeature.c b/arch/riscv/kernel/cpufeature.c
> > index 553d755483ed..3b5583db9d80 100644
> > --- a/arch/riscv/kernel/cpufeature.c
> > +++ b/arch/riscv/kernel/cpufeature.c
> > @@ -28,7 +28,7 @@ unsigned long elf_hwcap __read_mostly;
> >  /* Host ISA bitmap */
> >  static DECLARE_BITMAP(riscv_isa, RISCV_ISA_EXT_MAX) __read_mostly;
> >
> > -__ro_after_init DEFINE_STATIC_KEY_ARRAY_FALSE(riscv_isa_ext_keys, RISCV_ISA_EXT_KEY_MAX);
> > +DEFINE_STATIC_KEY_ARRAY_FALSE(riscv_isa_ext_keys, RISCV_ISA_EXT_KEY_MAX);
> >  EXPORT_SYMBOL(riscv_isa_ext_keys);
> >
> >  /**
> > --
> > 2.37.1
> >
> >
> > --
> > kvm-riscv mailing list
> > kvm-riscv@xxxxxxxxxxxxxxxxxxx
> > http://lists.infradead.org/mailman/listinfo/kvm-riscv
>
> Thanks for the quick fix. Tested with kvm guests booting in Qemu.
>
> Tested-by: Atish Patra <atishp@xxxxxxxxxxxx>

Thanks, I hadn't realized how static keys work but looks like having them as
__ro_after_init was always bogus.  Sorry to break stuff, looks like I should be
loading some module (probably KVM, as it's in the defconfig) during testing.

This is on fixes, I'm planning on sending it up later this week.