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[80.187.67.108]) by smtp.gmail.com with ESMTPSA id 4fb4d7f45d1cf-5c42bc8a51dsm3510875a12.97.2024.09.17.03.20.24 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 17 Sep 2024 03:20:25 -0700 (PDT) Message-ID: <4ced9211-2bd7-4257-a9fc-32c775ceffef@redhat.com> Date: Tue, 17 Sep 2024 12:20:22 +0200 Precedence: bulk X-Mailing-List: linux-fsdevel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH V2 1/7] m68k/mm: Change pmd_val() To: Anshuman Khandual , linux-mm@kvack.org Cc: Andrew Morton , Ryan Roberts , "Mike Rapoport (IBM)" , Arnd Bergmann , x86@kernel.org, linux-m68k@lists.linux-m68k.org, linux-fsdevel@vger.kernel.org, kasan-dev@googlegroups.com, linux-kernel@vger.kernel.org, linux-perf-users@vger.kernel.org, Geert Uytterhoeven , Guo Ren , Peter Zijlstra References: <20240917073117.1531207-1-anshuman.khandual@arm.com> <20240917073117.1531207-2-anshuman.khandual@arm.com> Content-Language: en-US From: David Hildenbrand Autocrypt: addr=david@redhat.com; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 17.09.24 09:31, Anshuman Khandual wrote: > This changes platform's pmd_val() to access the pmd_t element directly like > other architectures rather than current pointer address based dereferencing > that prevents transition into pmdp_get(). > > Cc: Geert Uytterhoeven > Cc: Guo Ren > Cc: Arnd Bergmann > Cc: linux-m68k@lists.linux-m68k.org > Cc: linux-kernel@vger.kernel.org > Signed-off-by: Anshuman Khandual > --- > arch/m68k/include/asm/page.h | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/arch/m68k/include/asm/page.h b/arch/m68k/include/asm/page.h > index 8cfb84b49975..be3f2c2a656c 100644 > --- a/arch/m68k/include/asm/page.h > +++ b/arch/m68k/include/asm/page.h > @@ -19,7 +19,7 @@ > */ > #if !defined(CONFIG_MMU) || CONFIG_PGTABLE_LEVELS == 3 > typedef struct { unsigned long pmd; } pmd_t; > -#define pmd_val(x) ((&x)->pmd) > +#define pmd_val(x) ((x).pmd) > #define __pmd(x) ((pmd_t) { (x) } ) > #endif > Trying to understand what's happening here, I stumbled over commit ef22d8abd876e805b604e8f655127de2beee2869 Author: Peter Zijlstra Date: Fri Jan 31 13:45:36 2020 +0100 m68k: mm: Restructure Motorola MMU page-table layout The Motorola 68xxx MMUs, 040 (and later) have a fixed 7,7,{5,6} page-table setup, where the last depends on the page-size selected (8k vs 4k resp.), and head.S selects 4K pages. For 030 (and earlier) we explicitly program 7,7,6 and 4K pages in %tc. However, the current code implements this mightily weird. What it does is group 16 of those (6 bit) pte tables into one 4k page to not waste space. The down-side is that that forces pmd_t to be a 16-tuple pointing to consecutive pte tables. This breaks the generic code which assumes READ_ONCE(*pmd) will be word sized. Where we did #if !defined(CONFIG_MMU) || CONFIG_PGTABLE_LEVELS == 3 -typedef struct { unsigned long pmd[16]; } pmd_t; -#define pmd_val(x) ((&x)->pmd[0]) -#define __pmd(x) ((pmd_t) { { (x) }, }) +typedef struct { unsigned long pmd; } pmd_t; +#define pmd_val(x) ((&x)->pmd) +#define __pmd(x) ((pmd_t) { (x) } ) #endif So I assume this should be fine Acked-by: David Hildenbrand -- Cheers, David / dhildenb