Re: [PATCHv2] arm64/cpufeature: don't use mutex in bringup path

[Suzuki K Poulose]

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.