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Date:   Wed, 25 Nov 2020 14:11:38 +0200
From:   Mike Rapoport <rppt@linux.ibm.com>
To:     David Hildenbrand <david@redhat.com>
Cc:     Mike Rapoport <rppt@kernel.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Alexander Viro <viro@zeniv.linux.org.uk>,
        Andy Lutomirski <luto@kernel.org>,
        Arnd Bergmann <arnd@arndb.de>, Borislav Petkov <bp@alien8.de>,
        Catalin Marinas <catalin.marinas@arm.com>,
        Christopher Lameter <cl@linux.com>,
        Dan Williams <dan.j.williams@intel.com>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        Elena Reshetova <elena.reshetova@intel.com>,
        "H. Peter Anvin" <hpa@zytor.com>, Ingo Molnar <mingo@redhat.com>,
        James Bottomley <jejb@linux.ibm.com>,
        "Kirill A. Shutemov" <kirill@shutemov.name>,
        Matthew Wilcox <willy@infradead.org>,
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Subject: Re: [PATCH v12 04/10] set_memory: allow querying whether
 set_direct_map_*() is actually enabled
Message-ID: <20201125121138.GJ123287@linux.ibm.com>
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 <5ea6eacd-79e8-0645-da39-d3461f60e627@redhat.com>
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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.