From mboxrd@z Thu Jan  1 00:00:00 1970
From: Suzuki.Poulose@arm.com (Suzuki K Poulose)
Date: Thu, 11 May 2017 16:54:27 +0100
Subject: [PATCHv2] arm64/cpufeature: don't use mutex in bringup path
In-Reply-To: <20170511153719.GB19626@leverpostej>
References: <1494514878-26878-1-git-send-email-mark.rutland@arm.com>
 <498b2e16-538a-d5ea-7843-2ebbff2007df@arm.com>
 <20170511153719.GB19626@leverpostej>
Message-ID: <232510f0-115e-b2c6-022f-03efd2606d56@arm.com>
To: linux-arm-kernel@lists.infradead.org
List-Id: linux-arm-kernel.lists.infradead.org

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.

Suzuki

>
> If so, I can do something like the above, patching <asm/virt.h> to use
> it for has_vhe().
>
> We don't have a BUG handler at hyp, but that should trigger a hyp panic,
> which I guess is good enough.
>
> Marc, thoughts?
>
> Thanks,
> Mark.
>