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X-CSE-ConnectionGUID: x/pmJqm4S5ehYT38e/xu5w== X-CSE-MsgGUID: kGebZl+VQgOcy3EOOJFngQ== X-IronPort-AV: E=McAfee;i="6800,10657,11735"; a="74145354" X-IronPort-AV: E=Sophos;i="6.23,130,1770624000"; d="scan'208";a="74145354" Received: from fmviesa009.fm.intel.com ([10.60.135.149]) by fmvoesa113.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 20 Mar 2026 12:42:28 -0700 X-CSE-ConnectionGUID: lu07U/svTcOi6H27MkjM+Q== X-CSE-MsgGUID: kCOGK3keQBSfNRoTO4D0Gg== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="6.23,130,1770624000"; d="scan'208";a="217205494" Received: from dnelso2-mobl.amr.corp.intel.com (HELO [10.125.109.109]) ([10.125.109.109]) by fmviesa009-auth.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 20 Mar 2026 12:42:27 -0700 Message-ID: <554c886f-6678-4208-8566-15aa140f6c4b@intel.com> Date: Fri, 20 Mar 2026 12:42:25 -0700 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 01/22] x86/mm: split out preallocate_sub_pgd() To: Brendan Jackman , Borislav Petkov , Dave Hansen , Peter Zijlstra , Andrew Morton , David Hildenbrand , Vlastimil Babka , Wei Xu , Johannes Weiner , Zi Yan , Lorenzo Stoakes Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, x86@kernel.org, rppt@kernel.org, Sumit Garg , derkling@google.com, reijiw@google.com, Will Deacon , rientjes@google.com, "Kalyazin, Nikita" , patrick.roy@linux.dev, "Itazuri, Takahiro" , Andy Lutomirski , David Kaplan , Thomas Gleixner , Yosry Ahmed References: <20260320-page_alloc-unmapped-v2-0-28bf1bd54f41@google.com> <20260320-page_alloc-unmapped-v2-1-28bf1bd54f41@google.com> From: Dave Hansen Content-Language: en-US Autocrypt: addr=dave.hansen@intel.com; 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charset=UTF-8 Content-Transfer-Encoding: 7bit On 3/20/26 11:23, Brendan Jackman wrote: > - /* > - * The goal here is to allocate all possibly required > - * hardware page tables pointed to by the top hardware > - * level. This comment is pretty important, IMNHO, and you zapped it. The problem here is that the per-MM carved out space is PGD-sized. You want to make sure there are page tables allocated for that space. But, if you say "go allocate a p4d" then that will collapse down to doing nothing on a 4-level system. So, this is effectively: Go allocate a p4d or pud, depending on if it's 4 or 5 level. Basically, always allocate the level that the hardware PGD points to. Could we put a comment to that effect around somewhere, please?