From mboxrd@z Thu Jan  1 00:00:00 1970
From: marc.zyngier@arm.com (Marc Zyngier)
Date: Thu, 11 May 2017 17:08:19 +0100
Subject: [PATCHv2] arm64/cpufeature: don't use mutex in bringup path
In-Reply-To: <232510f0-115e-b2c6-022f-03efd2606d56@arm.com>
References: <1494514878-26878-1-git-send-email-mark.rutland@arm.com>
 <498b2e16-538a-d5ea-7843-2ebbff2007df@arm.com>
 <20170511153719.GB19626@leverpostej>
 <232510f0-115e-b2c6-022f-03efd2606d56@arm.com>
Message-ID: <c6dfb0da-acec-620a-dba6-71aac6efce0b@arm.com>
To: linux-arm-kernel@lists.infradead.org
List-Id: linux-arm-kernel.lists.infradead.org

On 11/05/17 16:54, Suzuki K Poulose wrote:
> On 11/05/17 16:37, Mark Rutland wrote:
>> On Thu, May 11, 2017 at 04:15:38PM +0100, Suzuki K Poulose wrote:
>>> On 11/05/17 16:01, Mark Rutland wrote:
>>>> +static inline bool cpus_have_const_cap(int num)
>>>> +{
>>>> +	if (static_branch_likely(&arm64_const_caps_ready))
>>>> +		return __cpus_have_const_cap(num);
>>>> +	else
>>>> +		return cpus_have_cap(num);
>>>
>>> We use cpus_have_const_cap() from hyp code, via has_vhe() and we could potentially
>>> try to access unmapped kernel data from hyp if we fallback to cpus_have_cap().
>>> However, it looks like we have already set arm64_const_caps_ready, so should not
>>> hit it in practise. May be we could add a stricter version of the helper ?
>>>
>>> static inline cpus_have_const_cap_strict(int num)
>>> {
>>> 	BUG_ON(!static_branch_likely(&arm64_const_caps_ready);
>>> 	return __cpus_have_const_cap(num);
>>> }
>>
>> Just to check, is that the only user of cpus_have_const_cap() at hyp?
> 
> Uh, no we have one more, via system_supports_fpsimd() in __actvate_traps.

Indeed, and I'd definitely expect to see more of that trickling in (if
only to deal with errata).

I'm OK with the BUG_ON version, TBH. It's not pretty, but it will be
perfectly visible if it fires.

Thanks,

	M.
-- 
Jazz is not dead. It just smells funny...