From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 71406C433EF for ; Wed, 18 May 2022 16:36:58 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S240367AbiERQg4 (ORCPT ); Wed, 18 May 2022 12:36:56 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:35272 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S240526AbiERQga (ORCPT ); Wed, 18 May 2022 12:36:30 -0400 Received: from mga02.intel.com (mga02.intel.com [134.134.136.20]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 8C84D205C6 for ; Wed, 18 May 2022 09:36:29 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1652891789; x=1684427789; h=date:from:to:cc:subject:message-id:references: mime-version:in-reply-to; bh=nfxk6QHzxTv2778lb7oSutOL+8TQsowLGTPneGlEfdk=; b=np1D3I2P8vPJU91+uO9KSc4MtyVPqitXnHHMGgUq8J2YNJtiNhCsG/az U2h2bSUBA1yodBowRjvDP+uNsPSOErfwk8CmHZQvopOYQ0j7/KlvjWA2n hIut5T+YIfTNArKd61QCMFxbWNjNfo1qh2fi6i53xP0R4SiS360GIT+bi jSTdtuHdGxbeKmQLxaH3pfdWQEjRlcb0gV1CJFuPWO0Qrn8Wjs8saQNWV bjMt1wawr4/pIubll45Vk5mHBtWIQLH7TUoHAEsg4T0TAcuCl1fBdzdbm coYv7AcLkvCiD+P11+imZ0K4c9CJTjLbtGqXBf4RTgGUy97iNwjpAJnhE g==; X-IronPort-AV: E=McAfee;i="6400,9594,10351"; a="259332717" X-IronPort-AV: E=Sophos;i="5.91,235,1647327600"; d="scan'208";a="259332717" Received: from orsmga001.jf.intel.com ([10.7.209.18]) by orsmga101.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 18 May 2022 09:34:21 -0700 X-IronPort-AV: E=Sophos;i="5.91,235,1647327600"; d="scan'208";a="605971356" Received: from fyu1.sc.intel.com ([172.25.103.126]) by orsmga001-auth.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 18 May 2022 09:34:21 -0700 Date: Wed, 18 May 2022 09:34:48 -0700 From: Fenghua Yu To: Reinette Chatre Cc: Stephane Eranian , linux-kernel@vger.kernel.org, babu.moger@amd.com, x86@kernel.org Subject: Re: [PATCH v2] x86/resctrl: Fix zero cbm for AMD in cbm_validate Message-ID: References: <20220517001234.3137157-1-eranian@google.com> <5a634c10-103e-6f3e-e51b-db26b2bc90a5@intel.com> <0077efdf-ab64-2924-c290-cd940977b818@intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <0077efdf-ab64-2924-c290-cd940977b818@intel.com> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi, Babu, On Tue, May 17, 2022 at 11:10:40AM -0700, Reinette Chatre wrote: > On 5/17/2022 10:27 AM, Fenghua Yu wrote: > > On Tue, May 17, 2022 at 09:49:22AM -0700, Reinette Chatre wrote: > >> On 5/17/2022 9:33 AM, Fenghua Yu wrote: > >>> On Mon, May 16, 2022 at 05:12:34PM -0700, Stephane Eranian wrote: > >>>> AMD supports cbm with no bits set as reflected in rdt_init_res_defs_amd() by: > >>> ... > >>>> @@ -107,6 +107,10 @@ static bool cbm_validate(char *buf, u32 *data, struct rdt_resource *r) > >>>> first_bit = find_first_bit(&val, cbm_len); > >>>> zero_bit = find_next_zero_bit(&val, cbm_len, first_bit); > >>>> > >>>> + /* no need to check bits if arch supports no bits set */ > >>>> + if (r->cache.arch_has_empty_bitmaps && val == 0) > >>>> + goto done; > >>>> + > >>>> /* Are non-contiguous bitmaps allowed? */ > >>>> if (!r->cache.arch_has_sparse_bitmaps && > >>>> (find_next_bit(&val, cbm_len, zero_bit) < cbm_len)) { > >>>> @@ -119,7 +123,7 @@ static bool cbm_validate(char *buf, u32 *data, struct rdt_resource *r) > >>>> r->cache.min_cbm_bits); > >>>> return false; > >>>> } > >>>> - > >>>> +done: > >>>> *data = val; > >>>> return true; > >>>> } > >>> > >>> Isn't it AMD supports 0 minimal CBM bits? Then should set its min_cbm_bits as 0. > >>> Is the following patch a better fix? I don't have AMD machine and cannot > >>> test the patch. > >>> > >>> diff --git a/arch/x86/kernel/cpu/resctrl/core.c b/arch/x86/kernel/cpu/resctrl/core.c > >>> index 6055d05af4cc..031d77dd982d 100644 > >>> --- a/arch/x86/kernel/cpu/resctrl/core.c > >>> +++ b/arch/x86/kernel/cpu/resctrl/core.c > >>> @@ -909,6 +909,7 @@ static __init void rdt_init_res_defs_amd(void) > >>> r->cache.arch_has_sparse_bitmaps = true; > >>> r->cache.arch_has_empty_bitmaps = true; > >>> r->cache.arch_has_per_cpu_cfg = true; > >>> + r->cache.min_cbm_bits = 0; > >>> } else if (r->rid == RDT_RESOURCE_MBA) { > >>> hw_res->msr_base = MSR_IA32_MBA_BW_BASE; > >>> hw_res->msr_update = mba_wrmsr_amd; > >> > >> That is actually what Stephane's V1 [1] did and I proposed that > >> he fixes it with (almost) what he has in V2 (I think the check > >> can be moved earlier before any bits are searched for). > >> > >> The reasons why I proposed this change are: > >> - min_cbm_bits is a value that is exposed to user space and from the > >> time AMD was supported this has always been 1 for those systems. I > >> do not know how user space uses this value and unless I can be certain > >> making this 0 will not affect user space I would prefer not to > >> make such a change. > > > > But a user visible mismatch is created by the V2 patch: > > No. V2 does not create a user visible change, it restores original behavior. > > > User queries min_cbm_bits and finds it is 1 but turns out 0 can be written > > to the schemata. > > > > Is it an acceptable behavior? Shouldn't user read right min_cbm_bits (0) > > on AMD? > > Original AMD enabling set min_cbm_bits as 1 while also supporting 0 to > be written to schemata file. Supporting 0 to be written to schemata file > was unintentionally broken during one of the MPAM prep patches. This > patch fixes that. > > You are proposing a change to original AMD support that impacts user > space API while I find fixing to restore original behavior to > be the safest option. Perhaps Babu could pick the preferred solution > and I would step aside if you prefer to go with (an improved) V1. Is it OK for you to set min_cbm_bits to 0 on AMD? Thanks. -Fenghua