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X-CSE-ConnectionGUID: 3jZNrUcyQd66t2bOX5BGzA== X-CSE-MsgGUID: uwSlBacqRZWoAQLYqik5SQ== X-IronPort-AV: E=McAfee;i="6800,10657,11754"; a="76800907" X-IronPort-AV: E=Sophos;i="6.23,170,1770624000"; d="scan'208";a="76800907" Received: from orviesa001.jf.intel.com ([10.64.159.141]) by orvoesa110.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 09 Apr 2026 13:10:50 -0700 X-CSE-ConnectionGUID: afiw+rXDTcCnMhPvEjc1ZA== X-CSE-MsgGUID: Rht8fcv0SEyBGnk6fJ4FFQ== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="6.23,170,1770624000"; d="scan'208";a="266847968" Received: from ray2.jf.intel.com (HELO [10.24.81.183]) ([10.24.81.183]) by smtpauth.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 09 Apr 2026 13:10:49 -0700 Message-ID: <631bceef-d32b-475f-9d1a-644593aceddc@intel.com> Date: Thu, 9 Apr 2026 13:10:27 -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 v3 10/10] mm: thp: x86: cleanup PSE feature bit usage To: Zi Yan , Luiz Capitulino Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, david@kernel.org, baolin.wang@linux.alibaba.com, ryan.roberts@arm.com, akpm@linux-foundation.org, lorenzo.stoakes@oracle.com, Dave Hansen , Thomas Gleixner , Ingo Molnar , Borislav Petkov References: <16fe2db0becab98db70f53e4ce1422450a9f40ee.1775679721.git.luizcap@redhat.com> Content-Language: en-US From: Dave Hansen Autocrypt: addr=dave.hansen@intel.com; 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charset=UTF-8 Content-Transfer-Encoding: 7bit On 4/9/26 08:57, Zi Yan wrote: > Historically, THP support on x86 checked the PSE feature bit to enable > THP. On 64-bit, this check is redundant since PSE is always enabled by > default for compatibility. What do you mean by "PSE is always enabled by default"? A hypervisor is completely free to not enumerate PSE support to a guest. Any kernel can disable PSE with clearcpuid=3 on the command-line. PSE is also disabled for at least one erratum (which I think includes some 64-bit CPUs). Here's a snippet in a 64-bit VM of /proc/cpuinfo on a normal boot: DirectMap4k: 83836 kB DirectMap2M: 1939456 kB DirectMap1G: 1048576 kB and with clearcpuid=3: DirectMap4k: 3071868 kB DirectMap2M: 0 kB Just to show that it's possible. So perhaps I'm reading into the changelog too much, but this doesn't quite seem right to me.