From: Will Deacon <will@kernel.org>
To: Anshuman Khandual <anshuman.khandual@arm.com>
Cc: mark.rutland@arm.com, Suzuki K Poulose <suzuki.poulose@arm.com>,
Catalin Marinas <catalin.marinas@arm.com>,
linux-kernel@vger.kernel.org, Mark Brown <broonie@kernel.org>,
linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH V2] arm64/cpufeature: Add get_arm64_ftr_reg_nowarn()
Date: Wed, 27 May 2020 08:53:04 +0100 [thread overview]
Message-ID: <20200527075303.GC9887@willie-the-truck> (raw)
In-Reply-To: <ca38b2c0-533f-9b98-46a2-37ba8bf21d83@arm.com>
On Wed, May 27, 2020 at 07:56:30AM +0530, Anshuman Khandual wrote:
>
>
> On 05/27/2020 01:16 AM, Will Deacon wrote:
> > On Tue, May 26, 2020 at 04:01:35PM +0100, Catalin Marinas wrote:
> >> On Tue, May 26, 2020 at 07:09:13PM +0530, Anshuman Khandual wrote:
> >>> @@ -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;
> >>
> >> I think Will wanted an early return in all these functions not just
> >> removing the BUG_ON(). I'll let him clarify.
> >
> > Yes, the callers need to check the pointer and return early.
>
> Sure, will do. But for check_update_ftr_reg(), a feature register search
> failure should be treated as a success (0) or a failure (1). What should
> it return ? Seems bit tricky, as there are good reasons to go either way.
We're unable to check it so return 0, otherwise we'll randomly taint the
kernel and print a weird message.
Will
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prev parent reply other threads:[~2020-05-27 7:53 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-05-26 13:39 [PATCH V2] arm64/cpufeature: Add get_arm64_ftr_reg_nowarn() Anshuman Khandual
2020-05-26 14:04 ` Suzuki K Poulose
2020-05-26 14:03 ` Anshuman Khandual
2020-05-26 15:01 ` Catalin Marinas
2020-05-26 19:46 ` Will Deacon
2020-05-27 2:26 ` Anshuman Khandual
2020-05-27 7:53 ` Will Deacon [this message]
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