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From:   "Fabio M. De Francesco" <fmdefrancesco@gmail.com>
To:     David Sterba <dsterba@suse.com>,
        Andrew Morton <akpm@linux-foundation.org>
Cc:     Chris Mason <clm@fb.com>, Josef Bacik <josef@toxicpanda.com>,
        Nick Terrell <terrelln@fb.com>, linux-btrfs@vger.kernel.org,
        linux-kernel@vger.kernel.org, Ira Weiny <ira.weiny@intel.com>,
        Matthew Wilcox <willy@infradead.org>,
        Kees Cook <keescook@chromium.org>,
        Sebastian Andrzej Siewior <bigeasy@linutronix.de>,
        "James E . J . Bottomley" <James.Bottomley@hansenpartnership.com>,
        Helge Deller <deller@gmx.de>,
        John David Anglin <dave.anglin@bell.net>,
        linux-parisc@vger.kernel.org, David Sterba <dsterba@suse.cz>
Subject: Re: [RESEND PATCH v4 1/2] highmem: Make __kunmap_{local,atomic}() take "const void *"
Date:   Mon, 27 Jun 2022 19:02:31 +0200
Message-ID: <2192593.iZASKD2KPV@opensuse>
In-Reply-To: <20220616210037.7060-2-fmdefrancesco@gmail.com>
References: <20220616210037.7060-1-fmdefrancesco@gmail.com> <20220616210037.7060-2-fmdefrancesco@gmail.com>
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On gioved=C3=AC 16 giugno 2022 23:00:35 CEST Fabio M. De Francesco wrote:
> __kunmap_ {local,atomic}() currently take pointers to void. However, this
> is semantically incorrect, since these functions do not change the memory
> their arguments point to.
>=20
> Therefore, make this semantics explicit by modifying the prototypes of
> __kunmap_{local,atomic}() to take pointers to const void.
>=20
> As a side effect, compilers will likely produce more efficient code.
>=20
> Cc: Andrew Morton <akpm@linux-foundation.org>
> Suggested-by: David Sterba <dsterba@suse.cz>
> Suggested-by: Ira Weiny <ira.weiny@intel.com>
> Signed-off-by: Fabio M. De Francesco <fmdefrancesco@gmail.com>
> ---
>=20
> v3->v4: Cc Maintainers and mailing lists I had overlooked when I sent v3.
>=20
> v2->v3: Fix compilation errors for ARCH=3Dparisc.
>         Reported-by: kernel test robot <lkp@intel.com>
>=20
> v1->v2: Change the commit message to clearly explain why these functions
>         should require pointers to const void. The fundamental argument
>         behind the commit message changes is semantic correctness.
>         Obviously, there are no changes to the code.
>         Many thanks to David Sterba and Ira Weiny for suggestions and
>         reviews.
>
>  arch/parisc/include/asm/cacheflush.h |  6 +++---
>  arch/parisc/kernel/cache.c           |  2 +-
>  include/linux/highmem-internal.h     | 10 +++++-----
>  mm/highmem.c                         |  2 +-
>  4 files changed, 10 insertions(+), 10 deletions(-)

@Andrew:

Ira Weiny asked David Sterba for taking this patch through his tree because=
=20
it is a pre-requisite for a patch to fs/btrfs. He agreed with the above-
mentioned suggestion, however I suppose that an ACK by you is needed.

Can you please take a look at this patch and say what you think about it?

Thanks,

=46abio

>=20
> diff --git a/arch/parisc/include/asm/cacheflush.h b/arch/parisc/include/
asm/cacheflush.h
> index 8d03b3b26229..0bdee6724132 100644
> --- a/arch/parisc/include/asm/cacheflush.h
> +++ b/arch/parisc/include/asm/cacheflush.h
> @@ -22,7 +22,7 @@ void flush_kernel_icache_range_asm(unsigned long,=20
unsigned long);
>  void flush_user_dcache_range_asm(unsigned long, unsigned long);
>  void flush_kernel_dcache_range_asm(unsigned long, unsigned long);
>  void purge_kernel_dcache_range_asm(unsigned long, unsigned long);
> -void flush_kernel_dcache_page_asm(void *);
> +void flush_kernel_dcache_page_asm(const void *addr);
>  void flush_kernel_icache_page(void *);
> =20
>  /* Cache flush operations */
> @@ -31,7 +31,7 @@ void flush_cache_all_local(void);
>  void flush_cache_all(void);
>  void flush_cache_mm(struct mm_struct *mm);
> =20
> -void flush_kernel_dcache_page_addr(void *addr);
> +void flush_kernel_dcache_page_addr(const void *addr);
> =20
>  #define flush_kernel_dcache_range(start,size) \
>  	flush_kernel_dcache_range_asm((start), (start)+(size));
> @@ -75,7 +75,7 @@ void flush_dcache_page_asm(unsigned long phys_addr,=20
unsigned long vaddr);
>  void flush_anon_page(struct vm_area_struct *vma, struct page *page,=20
unsigned long vmaddr);
> =20
>  #define ARCH_HAS_FLUSH_ON_KUNMAP
> -static inline void kunmap_flush_on_unmap(void *addr)
> +static inline void kunmap_flush_on_unmap(const void *addr)
>  {
>  	flush_kernel_dcache_page_addr(addr);
>  }
> diff --git a/arch/parisc/kernel/cache.c b/arch/parisc/kernel/cache.c
> index c8a11fcecf4c..824064cafd61 100644
> --- a/arch/parisc/kernel/cache.c
> +++ b/arch/parisc/kernel/cache.c
> @@ -549,7 +549,7 @@ extern void purge_kernel_dcache_page_asm(unsigned=20
long);
>  extern void clear_user_page_asm(void *, unsigned long);
>  extern void copy_user_page_asm(void *, void *, unsigned long);
> =20
> -void flush_kernel_dcache_page_addr(void *addr)
> +void flush_kernel_dcache_page_addr(const void *addr)
>  {
>  	unsigned long flags;
> =20
> diff --git a/include/linux/highmem-internal.h b/include/linux/highmem-
internal.h
> index cddb42ff0473..034b1106d022 100644
> --- a/include/linux/highmem-internal.h
> +++ b/include/linux/highmem-internal.h
> @@ -8,7 +8,7 @@
>  #ifdef CONFIG_KMAP_LOCAL
>  void *__kmap_local_pfn_prot(unsigned long pfn, pgprot_t prot);
>  void *__kmap_local_page_prot(struct page *page, pgprot_t prot);
> -void kunmap_local_indexed(void *vaddr);
> +void kunmap_local_indexed(const void *vaddr);
>  void kmap_local_fork(struct task_struct *tsk);
>  void __kmap_local_sched_out(void);
>  void __kmap_local_sched_in(void);
> @@ -89,7 +89,7 @@ static inline void *kmap_local_pfn(unsigned long pfn)
>  	return __kmap_local_pfn_prot(pfn, kmap_prot);
>  }
> =20
> -static inline void __kunmap_local(void *vaddr)
> +static inline void __kunmap_local(const void *vaddr)
>  {
>  	kunmap_local_indexed(vaddr);
>  }
> @@ -121,7 +121,7 @@ static inline void *kmap_atomic_pfn(unsigned long=20
pfn)
>  	return __kmap_local_pfn_prot(pfn, kmap_prot);
>  }
> =20
> -static inline void __kunmap_atomic(void *addr)
> +static inline void __kunmap_atomic(const void *addr)
>  {
>  	kunmap_local_indexed(addr);
>  	pagefault_enable();
> @@ -197,7 +197,7 @@ static inline void *kmap_local_pfn(unsigned long pfn)
>  	return kmap_local_page(pfn_to_page(pfn));
>  }
> =20
> -static inline void __kunmap_local(void *addr)
> +static inline void __kunmap_local(const void *addr)
>  {
>  #ifdef ARCH_HAS_FLUSH_ON_KUNMAP
>  	kunmap_flush_on_unmap(addr);
> @@ -224,7 +224,7 @@ static inline void *kmap_atomic_pfn(unsigned long=20
pfn)
>  	return kmap_atomic(pfn_to_page(pfn));
>  }
> =20
> -static inline void __kunmap_atomic(void *addr)
> +static inline void __kunmap_atomic(const void *addr)
>  {
>  #ifdef ARCH_HAS_FLUSH_ON_KUNMAP
>  	kunmap_flush_on_unmap(addr);
> diff --git a/mm/highmem.c b/mm/highmem.c
> index 1a692997fac4..e32083e4ce0d 100644
> --- a/mm/highmem.c
> +++ b/mm/highmem.c
> @@ -561,7 +561,7 @@ void *__kmap_local_page_prot(struct page *page,=20
pgprot_t prot)
>  }
>  EXPORT_SYMBOL(__kmap_local_page_prot);
> =20
> -void kunmap_local_indexed(void *vaddr)
> +void kunmap_local_indexed(const void *vaddr)
>  {
>  	unsigned long addr =3D (unsigned long) vaddr & PAGE_MASK;
>  	pte_t *kmap_pte;
> --=20
> 2.36.1
>=20
>=20