Re: [PATCH v12 04/10] set_memory: allow querying whether set_direct_map_*() is actually enabled

Mike Rapoport
2020-11-25T12:12:30Z

On Wed, Nov 25, 2020 at 12:22:52PM +0100, David Hildenbrand wrote:
> > #include <asm-generic/cacheflush.h>
> >
> > #endif /* __ASM_CACHEFLUSH_H */
> > diff --git a/arch/arm64/include/asm/set_memory.h b/arch/arm64/include/asm/set_memory.h
> > new file mode 100644
> > index 000000000000..ecb6b0f449ab
> > --- /dev/null
> > +++ b/arch/arm64/include/asm/set_memory.h
> > @@ -0,0 +1,17 @@
> > +/* SPDX-License-Identifier: GPL-2.0-only */
> > +
> > +#ifndef _ASM_ARM64_SET_MEMORY_H
> > +#define _ASM_ARM64_SET_MEMORY_H
> > +
> > +#include <asm-generic/set_memory.h>
> > +
> > +bool can_set_direct_map(void);
> > +#define can_set_direct_map can_set_direct_map
>
> Well, that looks weird.
> [...]

We have a lot of those e.g. in linux/pgtable.h

> > }
> > +#else /* CONFIG_ARCH_HAS_SET_DIRECT_MAP */
> > +/*
> > + * Some architectures, e.g. ARM64 can disable direct map modifications at
> > + * boot time. Let them overrive this query.
> > + */
> > +#ifndef can_set_direct_map
> > +static inline bool can_set_direct_map(void)
> > +{
> > + return true;
> > +}
>
> I think we prefer __weak functions for something like that, avoids the
> ifdefery.

I'd prefer this for two reasons: first, static inline can be optimized
away and second, there is no really good place to put generic
implementation.

> Apart from that, LGTM.
>
> --
> Thanks,
>
> David / dhildenb
>

--
Sincerely yours,
Mike.