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

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Date:   Tue, 16 Aug 2022 21:29:36 -0700 (PDT)
From:   Palmer Dabbelt <palmer@...belt.com>
To:     atishp@...shpatra.org
CC:     ajones@...tanamicro.com, linux-riscv@...ts.infradead.org,
        kvm-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org,
        daolu@...osinc.com, jszhang@...nel.org, Conor.Dooley@...rochip.com,
        re@...z.net, apatel@...tanamicro.com
Subject:     Re: [PATCH] riscv: Ensure isa-ext static keys are writable

On Tue, 16 Aug 2022 16:41:46 PDT (-0700), atishp@...shpatra.org wrote:
> On Tue, Aug 16, 2022 at 9:31 AM Andrew Jones <ajones@...tanamicro.com> 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@...tanamicro.com>
>> ---
>>  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@...ts.infradead.org
>> 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@...osinc.com>

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.

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