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X-CSE-ConnectionGUID: CzvrluA6TUWV/9iheJMNTg== X-CSE-MsgGUID: qABAhx6ESz2HlCXfb72o7w== X-IronPort-AV: E=McAfee;i="6800,10657,11733"; a="74898854" X-IronPort-AV: E=Sophos;i="6.23,127,1770624000"; d="scan'208";a="74898854" Received: from orviesa005.jf.intel.com ([10.64.159.145]) by orvoesa109.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 18 Mar 2026 11:33:33 -0700 X-CSE-ConnectionGUID: BefRO6t1SPK9nlBjb0fong== X-CSE-MsgGUID: c60uFcnvReOWhYL/C0QfwA== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="6.23,127,1770624000"; d="scan'208";a="227666471" Received: from sghuge-mobl2.amr.corp.intel.com (HELO [10.125.109.14]) ([10.125.109.14]) by orviesa005-auth.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 18 Mar 2026 11:33:32 -0700 Message-ID: <0b568da8-d9c3-4e8b-9cce-e3b20add4a14@intel.com> Date: Wed, 18 Mar 2026 11:33:31 -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 From: Dave Hansen Subject: Re: [PATCH] x86/cpu: Add INVLPGB CPU feature flag to /proc/cpuinfo To: Yongting Lin Cc: babu.moger@amd.com, bp@alien8.de, dave.hansen@linux.intel.com, hpa@zytor.com, linux-kernel@vger.kernel.org, mingo@redhat.com, pawan.kumar.gupta@linux.intel.com, riel@surriel.com, seanjc@google.com, tglx@kernel.org, x86@kernel.org, xin@zytor.com References: <8012d986-0d1f-47a2-8892-2b2dcc1339db@intel.com> <20260318182341.26756-1-linyongting@bytedance.com> Content-Language: en-US Autocrypt: addr=dave.hansen@intel.com; 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charset=UTF-8 Content-Transfer-Encoding: 7bit On 3/18/26 11:23, Yongting Lin wrote: > On Wed, 18 Mar 2026 10:58:26 -0700, Dave Hansen wrote: >> On 3/18/26 10:52, Yongting Lin wrote: >>> commit 767ae437a32d ("x86/mm: Add INVLPGB feature and Kconfig entry") >>> introduced support for the INVLPGB instruction as a fast TLB >>> invalidation mechanism. However, no corresponding CPU feature flag is >>> exposed via /proc/cpuinfo. >> >> The patch is probably OK, but the changelog is insufficient. Could you >> please read through: >> >> Documentation/arch/x86/cpuinfo.rst >> >> and use that structure to construct a justification for why this feature >> is needed? > > Hi Dave, the invlpgb is a new ISA for newly AMD processors to issue a BROADCAST > operation to invalidate TLB entry in all remote CPUS, avoiding a cost of > IPI tlb flush operations. Heh, thanks for the background. > It should be visible to Linux user to be aware of this new feature as well > as application programs. I get it. But this doesn't tell me *why*. Did you happen to read the documentation I referenced above and asked you to read? I was hoping after you read it, you would understand which kinds of features we want in /proc/cpuinfo and which ones we don't. Then, you would be prepared to make a strong case for *why*.