linux-kernel - Re: [RESEND PATCH v4 1/2] highmem: Make __kunmap

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Message-ID: <Yr8qEp+us0e+FS/g@iweiny-desk3>
Date:   Fri, 1 Jul 2022 10:08:34 -0700
From:   Ira Weiny <ira.weiny@...el.com>
To:     "Fabio M. De Francesco" <fmdefrancesco@...il.com>
CC:     David Sterba <dsterba@...e.com>, Chris Mason <clm@...com>,
        Josef Bacik <josef@...icpanda.com>,
        Nick Terrell <terrelln@...com>, <linux-btrfs@...r.kernel.org>,
        <linux-mm@...ck.org>, <linux-kernel@...r.kernel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Matthew Wilcox <willy@...radead.org>,
        Kees Cook <keescook@...omium.org>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        "James E. J. Bottomley" <James.Bottomley@...senpartnership.com>,
        Helge Deller <deller@....de>,
        "John David Anglin" <dave.anglin@...l.net>,
        <linux-parisc@...r.kernel.org>, "David Sterba" <dsterba@...e.cz>
Subject: Re: [RESEND PATCH v4 1/2] highmem: Make __kunmap_{local,atomic}()
 take "const void *"

On Tue, Jun 28, 2022 at 04:46:49PM +0200, 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.
> 
> Therefore, make this semantics explicit by modifying the
> __kunmap_{local,atomic}() prototypes to take pointers to const void.
> 
> As a side effect, compilers will likely produce more efficient code.
> 
> Cc: Andrew Morton <akpm@...ux-foundation.org>
> Suggested-by: David Sterba <dsterba@...e.cz>
> Suggested-by: Ira Weiny <ira.weiny@...el.com>

Reviewed-by: Ira Weiny <ira.weiny@...el.com>

> Signed-off-by: Fabio M. De Francesco <fmdefrancesco@...il.com>
> ---
> 
> This is a resend of the same patch CC'ed to linux-mm.
> 
> v3->v4: Cc Maintainers and mailing lists I had overlooked when I sent v3.
> 
> v2->v3: Fix compilation errors for ARCH=parisc.
>         Reported-by: kernel test robot <lkp@...el.com>
> 
> 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(-)
> 
> 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, 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 *);
>  
>  /* 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);
>  
> -void flush_kernel_dcache_page_addr(void *addr);
> +void flush_kernel_dcache_page_addr(const void *addr);
>  
>  #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, unsigned long vaddr);
>  void flush_anon_page(struct vm_area_struct *vma, struct page *page, unsigned long vmaddr);
>  
>  #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 a9bc578e4c52..993999a65e54 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 long);
>  extern void clear_user_page_asm(void *, unsigned long);
>  extern void copy_user_page_asm(void *, void *, unsigned long);
>  
> -void flush_kernel_dcache_page_addr(void *addr)
> +void flush_kernel_dcache_page_addr(const void *addr)
>  {
>  	unsigned long flags;
>  
> 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);
>  }
>  
> -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 pfn)
>  	return __kmap_local_pfn_prot(pfn, kmap_prot);
>  }
>  
> -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));
>  }
>  
> -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 pfn)
>  	return kmap_atomic(pfn_to_page(pfn));
>  }
>  
> -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, pgprot_t prot)
>  }
>  EXPORT_SYMBOL(__kmap_local_page_prot);
>  
> -void kunmap_local_indexed(void *vaddr)
> +void kunmap_local_indexed(const void *vaddr)
>  {
>  	unsigned long addr = (unsigned long) vaddr & PAGE_MASK;
>  	pte_t *kmap_pte;
> -- 
> 2.36.1
> 
>