linux-kernel - [PATCH] mm/highmem: Align-down to page the address for kunmap_flush_on

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Message-Id: <20230126141144.11042-1-fmdefrancesco@gmail.com>
Date:   Thu, 26 Jan 2023 15:11:44 +0100
From:   "Fabio M. De Francesco" <fmdefrancesco@...il.com>
To:     Andrew Morton <akpm@...ux-foundation.org>,
        "Fabio M. De Francesco" <fmdefrancesco@...il.com>,
        Ira Weiny <ira.weiny@...el.com>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        Alexander Potapenko <glider@...gle.com>,
        Andrey Konovalov <andreyknvl@...il.com>,
        Tony Luck <tony.luck@...el.com>,
        Bagas Sanjaya <bagasdotme@...il.com>,
        David Sterba <dsterba@...e.com>,
        Kees Cook <keescook@...omium.org>,
        "Matthew Wilcox (Oracle)" <willy@...radead.org>,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org
Cc:     Al Viro <viro@...iv.linux.org.uk>, Helge Deller <deller@....de>
Subject: [PATCH] mm/highmem: Align-down to page the address for kunmap_flush_on_unmap()

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@...el.com>
Suggested-by: Al Viro <viro@...iv.linux.org.uk>
Confirmed-by: Helge Deller <deller@....de>
Confirmed-by: Matthew Wilcox <willy@...radead.org>
Fixes: f3ba3c710ac5 ("mm/highmem: Provide kmap_local*")
Signed-off-by: Fabio M. De Francesco <fmdefrancesco@...il.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