Re: [PATCH V2] arm64/cpufeature: Add get_arm64_ftr_reg_nowarn()

Suzuki K Poulose
2020-05-26T13:59:42Z

On 05/26/2020 02:39 PM, Anshuman Khandual wrote:
> There is no way to proceed when requested register could not be searched in
> arm64_ftr_reg[]. Requesting for a non present register would be an error as
> well. Hence lets just WARN_ON() when search fails in get_arm64_ftr_reg()
> rather than checking for return value and doing a BUG_ON() instead in some
> individual callers. But there are also caller instances that dont error out
> when register search fails. Add a new helper get_arm64_ftr_reg_nowarn() for
> such cases.
>
> Cc: Catalin Marinas <catalin.marinas@arm.com>
> Cc: Will Deacon <will@kernel.org>
> Cc: Suzuki K Poulose <suzuki.poulose@arm.com>
> Cc: Mark Brown <broonie@kernel.org>
> Cc: linux-arm-kernel@lists.infradead.org
> Cc: linux-kernel@vger.kernel.org
> Signed-off-by: Anshuman Khandual <anshuman.khandual@arm.com>
> ---
> Changes in V2:
>
> - Added get_arm64_ftr_reg_nowarn() per Will
> - read_sanitised_ftr_reg() returns 0 when register search fails per Catalin
>
> Changes in V1: (https://patchwork.kernel.org/patch/11559083/)
>
> arch/arm64/kernel/cpufeature.c | 42 +++++++++++++++++++++++-----------
> 1 file changed, 29 insertions(+), 13 deletions(-)
>
> diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
> index bc5048f152c1..f4555b9d145c 100644
> --- a/arch/arm64/kernel/cpufeature.c
> +++ b/arch/arm64/kernel/cpufeature.c
> @@ -548,16 +548,16 @@ static int search_cmp_ftr_reg(const void *id, const void *regp)
> }
>

...

> static u64 arm64_ftr_set_value(const struct arm64_ftr_bits *ftrp, s64 reg,
> s64 ftr_val)
> {
> @@ -632,8 +654,6 @@ static void __init init_cpu_ftr_reg(u32 sys_reg, u64 new)
> const struct arm64_ftr_bits *ftrp;
> struct arm64_ftr_reg *reg = get_arm64_ftr_reg(sys_reg);
>
> - BUG_ON(!reg);
> -
> for (ftrp = reg->ftr_bits; ftrp->width; ftrp++) {
> u64 ftr_mask = arm64_ftr_mask(ftrp);
> s64 ftr_new = arm64_ftr_value(ftrp, new);
> @@ -762,7 +782,6 @@ static int check_update_ftr_reg(u32 sys_id, int cpu, u64 val, u64 boot)
> {
> struct arm64_ftr_reg *regp = get_arm64_ftr_reg(sys_id);
>
> - BUG_ON(!regp);
> update_cpu_ftr_reg(regp, val);
> if ((boot & regp->strict_mask) == (val & regp->strict_mask))
> return 0;
> @@ -776,9 +795,6 @@ static void relax_cpu_ftr_reg(u32 sys_id, int field)
> const struct arm64_ftr_bits *ftrp;
> struct arm64_ftr_reg *regp = get_arm64_ftr_reg(sys_id);
>
> - if (WARN_ON(!regp))
> - return;
> -

You need to return here, on !regp. Rest looks fine to me.

Suzuki