From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from shelob.surriel.com (shelob.surriel.com [96.67.55.147]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id B608917548 for ; Sat, 29 Mar 2025 17:29:37 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=96.67.55.147 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1743269393; cv=none; b=kEFF4Xw1MaL6c1bp6AcG+c3iGO2FaYfUmtujo0EmxuwvAP7VpC4nMsVtieb+Ei4ftaI9pevOYdQJkPO1OhUc2J4br0O5MADgoS6oi7tMYdflZVRbulz3amZWZWBaBmy7fTo6iO3acoOSpLofL3LNJd0u/URgRWbWJH3CXNhjfGI= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1743269393; c=relaxed/simple; bh=imUYZ/W/GVleMNjiWv15mGu860oaVQw7PlgELqcSTqw=; h=Message-ID:Subject:From:To:Cc:Date:In-Reply-To:References: Content-Type:MIME-Version; b=dfDVq7/3tM8NgS7/06YcJvzuDpazJLc9zptuCkTdFI1XhoaS6GtZxmRsjEl6esysBG8B+y2osTEOZWHb9rDW0vlePr3EyPgBXtxwuuxCEo5ocuzUu5xZVO99J8WnDj3c7y6HLIA3BMDiS2vx8PjS8BXKf5yvOqFEN386TtkmUnk= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=surriel.com; spf=pass smtp.mailfrom=shelob.surriel.com; arc=none smtp.client-ip=96.67.55.147 Authentication-Results: smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=surriel.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=shelob.surriel.com Received: from fangorn.home.surriel.com ([10.0.13.7]) by shelob.surriel.com with esmtpsa (TLS1.2) tls TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 (Exim 4.97.1) (envelope-from ) id 1tyZzp-000000006vT-45Ph; Sat, 29 Mar 2025 13:29:25 -0400 Message-ID: Subject: Re: [PATCH 1/3] x86/mm: Correct the actual count of available global ASIDs From: Rik van Riel To: Hou Wenlong , linux-kernel@vger.kernel.org Cc: Dave Hansen , Andy Lutomirski , Peter Zijlstra , Thomas Gleixner , Ingo Molnar , Borislav Petkov , x86@kernel.org, "H. Peter Anvin" Date: Sat, 29 Mar 2025 13:29:25 -0400 In-Reply-To: <0954cb7ec766d6d1e0b66a93876762b516ae9bae.1743250122.git.houwenlong.hwl@antgroup.com> References: <0954cb7ec766d6d1e0b66a93876762b516ae9bae.1743250122.git.houwenlong.hwl@antgroup.com> Autocrypt: addr=riel@surriel.com; prefer-encrypt=mutual; keydata=mQENBFIt3aUBCADCK0LicyCYyMa0E1lodCDUBf6G+6C5UXKG1jEYwQu49cc/gUBTTk33A eo2hjn4JinVaPF3zfZprnKMEGGv4dHvEOCPWiNhlz5RtqH3SKJllq2dpeMS9RqbMvDA36rlJIIo47 Z/nl6IA8MDhSqyqdnTY8z7LnQHqq16jAqwo7Ll9qALXz4yG1ZdSCmo80VPetBZZPw7WMjo+1hByv/ lvdFnLfiQ52tayuuC1r9x2qZ/SYWd2M4p/f5CLmvG9UcnkbYFsKWz8bwOBWKg1PQcaYHLx06sHGdY dIDaeVvkIfMFwAprSo5EFU+aes2VB2ZjugOTbkkW2aPSWTRsBhPHhV6dABEBAAG0HlJpayB2YW4gU mllbCA8cmllbEByZWRoYXQuY29tPokBHwQwAQIACQUCW5LcVgIdIAAKCRDOed6ShMTeg05SB/986o gEgdq4byrtaBQKFg5LWfd8e+h+QzLOg/T8mSS3dJzFXe5JBOfvYg7Bj47xXi9I5sM+I9Lu9+1XVb/ r2rGJrU1DwA09TnmyFtK76bgMF0sBEh1ECILYNQTEIemzNFwOWLZZlEhZFRJsZyX+mtEp/WQIygHV WjwuP69VJw+fPQvLOGn4j8W9QXuvhha7u1QJ7mYx4dLGHrZlHdwDsqpvWsW+3rsIqs1BBe5/Itz9o 6y9gLNtQzwmSDioV8KhF85VmYInslhv5tUtMEppfdTLyX4SUKh8ftNIVmH9mXyRCZclSoa6IMd635 Jq1Pj2/Lp64tOzSvN5Y9zaiCc5FucXtB9SaWsgdmFuIFJpZWwgPHJpZWxAc3VycmllbC5jb20+iQE +BBMBAgAoBQJSLd2lAhsjBQkSzAMABgsJCAcDAgYVCAIJCgsEFgIDAQIeAQIXgAAKCRDOed6ShMTe g4PpB/0ZivKYFt0LaB22ssWUrBoeNWCP1NY/lkq2QbPhR3agLB7ZXI97PF2z/5QD9Fuy/FD/jddPx KRTvFCtHcEzTOcFjBmf52uqgt3U40H9GM++0IM0yHusd9EzlaWsbp09vsAV2DwdqS69x9RPbvE/Ne fO5subhocH76okcF/aQiQ+oj2j6LJZGBJBVigOHg+4zyzdDgKM+jp0bvDI51KQ4XfxV593OhvkS3z 3FPx0CE7l62WhWrieHyBblqvkTYgJ6dq4bsYpqxxGJOkQ47WpEUx6onH+rImWmPJbSYGhwBzTo0Mm G1Nb1qGPG+mTrSmJjDRxrwf1zjmYqQreWVSFEt26tBpSaWsgdmFuIFJpZWwgPHJpZWxAZmIuY29tP okBPgQTAQIAKAUCW5LbiAIbIwUJEswDAAYLCQgHAwIGFQgCCQoLBBYCAwECHgECF4AACgkQznneko TE3oOUEQgAsrGxjTC1bGtZyuvyQPcXclap11Ogib6rQywGYu6/Mnkbd6hbyY3wpdyQii/cas2S44N cQj8HkGv91JLVE24/Wt0gITPCH3rLVJJDGQxprHTVDs1t1RAbsbp0XTksZPCNWDGYIBo2aHDwErhI omYQ0Xluo1WBtH/UmHgirHvclsou1Ks9jyTxiPyUKRfae7GNOFiX99+ZlB27P3t8CjtSO831Ij0Ip QrfooZ21YVlUKw0Wy6Ll8EyefyrEYSh8KTm8dQj4O7xxvdg865TLeLpho5PwDRF+/mR3qi8CdGbkE c4pYZQO8UDXUN4S+pe0aTeTqlYw8rRHWF9TnvtpcNzZw== Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable User-Agent: Evolution 3.54.3 (3.54.3-1.fc41) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Sender: riel@surriel.com On Sat, 2025-03-29 at 21:05 +0800, Hou Wenlong wrote: >=20 > +++ b/arch/x86/mm/tlb.c > @@ -279,7 +279,7 @@ static DEFINE_RAW_SPINLOCK(global_asid_lock); > =C2=A0static u16 last_global_asid =3D MAX_ASID_AVAILABLE; > =C2=A0static DECLARE_BITMAP(global_asid_used, MAX_ASID_AVAILABLE); > =C2=A0static DECLARE_BITMAP(global_asid_freed, MAX_ASID_AVAILABLE); > -static int global_asid_available =3D MAX_ASID_AVAILABLE - > TLB_NR_DYN_ASIDS - 1; > +static int global_asid_available =3D MAX_ASID_AVAILABLE - > TLB_NR_DYN_ASIDS; Unfortunately we are limited by the PCID space. A process with ASID N will get PCID N+1. The PCID space has the same size (and maximum value) as the ASID space. That means we cannot use the top ASID value. Alternatively, I suppose we could have ASID and PCID line up, and always exclude ASID 0 from being used. That might (maybe) be prettier code, but it isn't what we have today. --=20 All Rights Reversed.