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[68.111.84.250]) by smtp.gmail.com with ESMTPSA id y10sm12205852pjr.2.2020.11.07.20.54.14 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Sat, 07 Nov 2020 20:54:15 -0800 (PST) Subject: Re: [PATCH] mm/zsmalloc: include sparsemem.h for MAX_PHYSMEM_BITS To: Stefan Agner , Andrew Morton Cc: minchan@kernel.org, ngupta@vflare.org, sergey.senozhatsky.work@gmail.com, sjenning@linux.vnet.ibm.com, gregkh@linuxfoundation.org, arnd@arndb.de, linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <20201107165645.1b139b595b6b64feaca61bcb@linux-foundation.org> From: Florian Fainelli Message-ID: <29cb13a4-e10d-a394-3c00-1d7721a2dc0a@gmail.com> Date: Sat, 7 Nov 2020 20:54:13 -0800 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:78.0) Gecko/20100101 Firefox/78.0 Thunderbird/78.4.1 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 11/7/2020 5:16 PM, Stefan Agner wrote: > On 2020-11-08 01:56, Andrew Morton wrote: >> On Sat, 7 Nov 2020 16:22:06 +0100 Stefan Agner wrote: >> >>> Most architectures define MAX_PHYSMEM_BITS in asm/sparsemem.h and don't >>> include it in asm/pgtable.h. Include asm/sparsemem.h directly to get >>> the MAX_PHYSMEM_BITS define on all architectures. >>> >>> This fixes a crash when accessing zram on 32-bit ARM platform with LPAE and >>> more than 4GB of memory: >>> Unable to handle kernel NULL pointer dereference at virtual address 00000000 >> >> Mysterious. Presumably without this include, some compilation unit is >> picking up the wrong value of MAX_PHYSMEM_BITS? But I couldn't >> actually see where/how this occurs. Can you please explain further? > > Not sure if I got that right, but from what I understand if > MAX_PHYSMEM_BITS is not set in mm/zsmalloc.c it will set > MAX_PHYSMEM_BITS to BITS_PER_LONG. And this is 32-bit, too short when > LPAE is in use... You should probably include this in your commit message since that is describing the bug and then your fix makes complete sense. -- Florian