If ARCH_HAS_FLUSH_ON_KUNMAP is defined (PA-RISC case), __kunmap_local()
calls kunmap_flush_on_unmap(). The latter currently flushes the wrong
address (as confirmed by Matthew Wilcox and Helge Deller). Al Viro
proposed to call kunmap_flush_on_unmap() on an aligned-down to page
address in order to fix this issue. Consensus has been reached on this
solution.

Therefore, if ARCH_HAS_FLUSH_ON_KUNMAP is defined, call
kunmap_flush_on_unmap() on an aligned-down to page address computed with
the PTR_ALIGN_DOWN() macro.

Cc: Ira Weiny <ira.weiny@intel.com>
Suggested-by: Al Viro <viro@zeniv.linux.org.uk>
Confirmed-by: Helge Deller <deller@gmx.de>
Confirmed-by: Matthew Wilcox <willy@infradead.org>
Fixes: f3ba3c710ac5 ("mm/highmem: Provide kmap_local*")
Signed-off-by: Fabio M. De Francesco <fmdefrancesco@gmail.com>
---

I have (at least) two problems with this patch...

1) checkpatch.pl complains about the use of the non-standard
"Confirmed-by" tags. I don't know how else I can give credit to Helge
and Matthew. However, this is not the first time that I see non-standard
tags in patches applied upstream (I too had a non-standard
"Analysed-by" tag in patch which fixes a SAC bug). Any objections?

2) I'm not sure whether or not the "Fixes" tag is appropriate in this
patch. Can someone either confirm or deny it?

 include/linux/highmem-internal.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/include/linux/highmem-internal.h b/include/linux/highmem-internal.h
index 034b1106d022..e247c9ac4583 100644
--- a/include/linux/highmem-internal.h
+++ b/include/linux/highmem-internal.h
@@ -200,7 +200,7 @@ static inline void *kmap_local_pfn(unsigned long pfn)
 static inline void __kunmap_local(const void *addr)
 {
 #ifdef ARCH_HAS_FLUSH_ON_KUNMAP
-	kunmap_flush_on_unmap(addr);
+	kunmap_flush_on_unmap(PTR_ALIGN_DOWN(addr, PAGE_SIZE));
 #endif
 }
 
-- 
2.39.0

On giovedì 26 gennaio 2023 15:11:44 CET Fabio M. De Francesco wrote:
> If ARCH_HAS_FLUSH_ON_KUNMAP is defined (PA-RISC case), __kunmap_local()
> calls kunmap_flush_on_unmap(). The latter currently flushes the wrong
> address (as confirmed by Matthew Wilcox and Helge Deller). Al Viro
> proposed to call kunmap_flush_on_unmap() on an aligned-down to page
> address in order to fix this issue. Consensus has been reached on this
> solution.
> 
> Therefore, if ARCH_HAS_FLUSH_ON_KUNMAP is defined, call
> kunmap_flush_on_unmap() on an aligned-down to page address computed with
> the PTR_ALIGN_DOWN() macro.
> 
> Cc: Ira Weiny <ira.weiny@intel.com>
> Suggested-by: Al Viro <viro@zeniv.linux.org.uk>
> Confirmed-by: Helge Deller <deller@gmx.de>
> Confirmed-by: Matthew Wilcox <willy@infradead.org>
> Fixes: f3ba3c710ac5 ("mm/highmem: Provide kmap_local*")
> Signed-off-by: Fabio M. De Francesco <fmdefrancesco@gmail.com>
> ---
> 
> I have (at least) two problems with this patch...
> 
> 1) checkpatch.pl complains about the use of the non-standard
> "Confirmed-by" tags. I don't know how else I can give credit to Helge
> and Matthew. However, this is not the first time that I see non-standard
> tags in patches applied upstream (I too had a non-standard
> "Analysed-by" tag in patch which fixes a SAC bug). Any objections?
> 
> 2) I'm not sure whether or not the "Fixes" tag is appropriate in this
> patch. Can someone either confirm or deny it?
> 
>  include/linux/highmem-internal.h | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/include/linux/highmem-internal.h
> b/include/linux/highmem-internal.h index 034b1106d022..e247c9ac4583 100644
> --- a/include/linux/highmem-internal.h
> +++ b/include/linux/highmem-internal.h
> @@ -200,7 +200,7 @@ static inline void *kmap_local_pfn(unsigned long pfn)
>  static inline void __kunmap_local(const void *addr)
>  {
>  #ifdef ARCH_HAS_FLUSH_ON_KUNMAP
> -	kunmap_flush_on_unmap(addr);
> +	kunmap_flush_on_unmap(PTR_ALIGN_DOWN(addr, PAGE_SIZE));
>  #endif
>  }
> 
> --
> 2.39.0

I just realized that I forgot to Cc Thomas Gleixner. Therefore, I think I'd 
better add him to the list and resend this patch. 

I'm doing it immediately, so please drop this.

Thanks,

Fabio