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Tue, 13 Oct 2020 16:15:00 +0000 From: Steve Capper Subject: Re: [PATCH v2 1/4] arm64: mm: use single quantity to represent the PA to VA translation To: Ard Biesheuvel , linux-arm-kernel@lists.infradead.org References: <20201008153602.9467-1-ardb@kernel.org> <20201008153602.9467-2-ardb@kernel.org> Message-ID: Date: Tue, 13 Oct 2020 17:14:52 +0100 User-Agent: Mozilla/5.0 (Windows NT 10.0; rv:78.0) Gecko/20100101 Thunderbird/78.3.2 In-Reply-To: <20201008153602.9467-2-ardb@kernel.org> Content-Language: en-GB X-Originating-IP: [217.140.99.251] X-ClientProxiedBy: DM5PR17CA0065.namprd17.prod.outlook.com (2603:10b6:3:13f::27) To DB8PR08MB4986.eurprd08.prod.outlook.com (2603:10a6:10:e0::18) MIME-Version: 1.0 X-MS-Exchange-MessageSentRepresentingType: 1 Received: from [10.57.17.169] (217.140.99.251) by DM5PR17CA0065.namprd17.prod.outlook.com (2603:10b6:3:13f::27) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.3455.23 via Frontend Transport; Tue, 13 Oct 2020 16:14:58 +0000 X-MS-PublicTrafficType: Email X-MS-Office365-Filtering-HT: Tenant X-MS-Office365-Filtering-Correlation-Id: a1823606-741e-4043-a3d4-08d86f9897d2 X-MS-TrafficTypeDiagnostic: DBBPR08MB6219:|DBAPR08MB5749: X-MS-Exchange-Transport-Forked: True X-Microsoft-Antispam-PRVS: x-checkrecipientrouted: true NoDisclaimer: true X-MS-Oob-TLC-OOBClassifiers: OLM:10000;OLM:10000; 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charset="us-ascii"; Format="flowed" Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org Hi Ard, On 08/10/2020 16:35, Ard Biesheuvel wrote: > On arm64, the global variable memstart_addr represents the physical > address of PAGE_OFFSET, and so physical to virtual translations or > vice versa used to come down to simple additions or subtractions > involving the values of PAGE_OFFSET and memstart_addr. > > When support for 52-bit virtual addressing was introduced, we had to > deal with PAGE_OFFSET potentially being outside of the region that > can be covered by the virtual range (as the 52-bit VA capable build > needs to be able to run on systems that are only 48-bit VA capable), > and for this reason, another translation was introduced, and recorded > in the global variable physvirt_offset. > > However, if we go back to the original definition of memstart_addr, > i.e., the physical address of PAGE_OFFSET, it turns out that there is > no need for two separate translations: instead, we can simply subtract > the size of the unaddressable VA space from memstart_addr to make the > available physical memory appear in the 48-bit addressable VA region. > > This simplifies things, but also fixes a bug on KASLR builds, which > may update memstart_addr later on in arm64_memblock_init(), but fails > to update vmemmap and physvirt_offset accordingly. > Apologies, I didn't spot that before. > Fixes: 5383cc6efed13 ("arm64: mm: Introduce vabits_actual") > Signed-off-by: Ard Biesheuvel Thanks for this. It is much better to modify memstart_addr rather than introducing needless complexity. Reviewed-by: Steve Capper Cheers, -- Steve _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel