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Message-ID: Date: Tue, 20 Aug 2024 12:48:13 +0100 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v3 2/4] xen: make VMAP only support in MMU system Content-Language: en-GB To: Julien Grall , Ayan Kumar Halder Cc: xen-devel@lists.xenproject.org, Penny Zheng , Wei Chen , sstabellini@kernel.org, bertrand.marquis@arm.com, michal.orzel@amd.com, Jan Beulich , Volodymyr_Babchuk@epam.com References: <20240813171356.46760-1-ayan.kumar.halder@amd.com> <20240813171356.46760-3-ayan.kumar.halder@amd.com> <6d333d94-80ad-485c-b024-a45a388b96a4@suse.com> <597b358e-3b45-4fba-922d-31208b55d15a@amd.com> <9fd1801c-1460-44e5-b066-f6da1167543b@xen.org> <1a328f00-3b0d-4e9c-856c-97c3a80dfdef@amd.com> <55a91ace-a76f-40b9-bdb2-49f816006612@xen.org> From: Ayan Kumar Halder In-Reply-To: <55a91ace-a76f-40b9-bdb2-49f816006612@xen.org> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-ClientProxiedBy: LO2P265CA0112.GBRP265.PROD.OUTLOOK.COM (2603:10a6:600:c::28) To PH8PR12MB7326.namprd12.prod.outlook.com (2603:10b6:510:216::7) MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: PH8PR12MB7326:EE_|DS0PR12MB7726:EE_ X-MS-Office365-Filtering-Correlation-Id: 675598e4-811f-40a2-32d6-08dcc10dfbf8 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|1800799024|376014|366016; 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This has the benefit that the change can be >>> contained within arch/arm if we do the following :- >>> >>> diff --git a/xen/arch/arm/setup.c b/xen/arch/arm/setup.c >>> index cb2c0a16b8..26f7406278 100644 >>> --- a/xen/arch/arm/setup.c >>> +++ b/xen/arch/arm/setup.c >>> @@ -329,7 +329,9 @@ void asmlinkage __init start_xen(unsigned long >>> boot_phys_offset, >>> >>>       setup_mm(); >>> >>> +#ifdef CONFIG_MMU >>>       vm_init(); >>> +#endif >>> >>>       /* Parse the ACPI tables for possible boot-time configuration */ >>>       acpi_boot_table_init(); >>> >>> Are we ok with this ? >>> >>> The definition of vm_init() is in xen/include/xen/vmap.h. If I >>> enclose it using any CONFIG_XXX (like I have done in the current >>> patch), then I need to introduce it in common/Kconfig and define it >>> for x86 and PPC. I would prefer to contain the change within >>> arch/arm only if possible. >> >> Just to clarify, are you suggesting to just protect the call >> vm_init(). In other word, common/vmap.c would still be included in >> the final binary for the MPU? >> >> If yes, then I think it would be a bit odd... Someone could still >> call vmap() and this would not break until runtime. >> >> So I don't see how we could get away from modifying the common code. > > Readying my previous reply again. I think the confusion comes from: > > > But maybe ARCH_VMAP was an incorrect suggestion. It might be better > to gate with the !MMU (IIRC this would imply MPU). > > This was specifically referring to the branch predictor Kconfig. This > was not a suggestion to avoid introducing ARCH_VMAP. Thanks for clarifying this. Yes, I misunderstood your previous comment. So I will do :- 1. HARDEN_BRANCH_PREDICTOR will depend on MMU. 2. ARCH_VMAP will be selected by PPC and RISCV. The reason is below. 3. xen/common/vmap.c will be conditionally compiled on ARCH_VMAP and the "#ifdef VMAP_VIRT_START .. endif" will be from removed within the file. As VMAP_VIRT_START is defined by RISCV and PPC, thus #2 is needed. Julien, Jan :- Please let me know if you are ok with #3. This was in response to Michal's comment. While his suggestion makes sense, I am not sure if extending the changes to other architectures is the correct approach. Or do you prefer keeping xen/common/vmap.c unchanged. Kind regards, Ayan > > Cheers, >