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 X-Spam-Level: X-Spam-Status: No, score=-26.3 required=3.0 tests=BAYES_00,DKIMWL_WL_MED, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, USER_AGENT_GIT,USER_IN_DEF_DKIM_WL autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id B5CB8C433E2 for ; Wed, 31 Mar 2021 00:50:36 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id A1678619D7 for ; Wed, 31 Mar 2021 00:50:36 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232869AbhCaAuF (ORCPT ); Tue, 30 Mar 2021 20:50:05 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:38418 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232515AbhCaAtv (ORCPT ); Tue, 30 Mar 2021 20:49:51 -0400 Received: from mail-qk1-x749.google.com (mail-qk1-x749.google.com [IPv6:2607:f8b0:4864:20::749]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id A0E3EC061762 for ; Tue, 30 Mar 2021 17:49:50 -0700 (PDT) Received: by mail-qk1-x749.google.com with SMTP id b127so326632qkf.19 for ; Tue, 30 Mar 2021 17:49:50 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20161025; h=reply-to:date:in-reply-to:message-id:mime-version:references :subject:from:to:cc; bh=0pQ01a6Xvm310A3j8LcU50M1ntMFUct1qAGwe2for/I=; b=M9zMkM0gUqc7cw+RxOeX9G/PPlsC6SW+jLTCgvz0C/xa3gwqK4tgcFoEzmM3OCdLzr N2yPBFu/OH3lDcvhkvTonWi9HpbQshUZ8aUT5DqALEfUAoltXzstN7MDFv5FZmY54PQo PImKhz1Y2Tg1FhNQKkn6zSzJl3mU4duB7MiiVpe+w+EHXFBnsEl9khGH61hqa9Cj+L1p xmFu0rcuNN18H7VVhKb3/U45OPqOWoYJeaNYI/cWh+CSMpxn19fsUAR4rVS6GofJ+e2L 6xD13vOZxEHX9yng8jrzP/FNmRThNY/mVtW2LOW/VyJipkZyKYfg4HCJ4H/sHogLOmiy yVLg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:reply-to:date:in-reply-to:message-id :mime-version:references:subject:from:to:cc; bh=0pQ01a6Xvm310A3j8LcU50M1ntMFUct1qAGwe2for/I=; b=bVRJm3I8gT6el8fqlNq55kmQMSa/FRVXlmPS9Y+bAxwbbA54KEcV4xPZyI8uZ2cw2F oD53ulfRH44Zdcpsgqqm4WUO7bs8W383SLP31Rrv3TS142Elu7uTGfjjcOLO8e/9+rN7 kKhHV59sekJOZo0lEQzMXZ2kwKOPM0njlaPoyFj98upHB+va7RP771q+wmV4ragJR+o0 789JoPjdpNQbkJtxAAcIUj+e2yMn7+7VB9U7ycQJavPVvfAlhdBDABLxrMmEjwLoaQZX q8cayfUIJ0JceAz4vnev0hJI3kjT0TVb8EsQXjG2xweRJWZ47apUBYiVPU0h6Tq7N3BM 6PBg== X-Gm-Message-State: AOAM532E4WMPCAMpoOMXjHfYuE3dCdrfQ2NoShuO/+M15rTg/dKgtRJC ngj2yE1kyGJE87Xh5KxBuu79tnYNArc= X-Google-Smtp-Source: ABdhPJzrR2EtxZGC1kDYZcmX9KPmGp0qbO2gZiVLBiZ0lyQfYYpAA0wJAgSyOkt4jnihlIT9dxUd0jWr8Tc= X-Received: from seanjc798194.pdx.corp.google.com ([2620:15c:f:10:6c6b:5d63:9b3b:4a77]) (user=seanjc job=sendgmr) by 2002:a05:6214:8c4:: with SMTP id da4mr644183qvb.17.1617151789751; Tue, 30 Mar 2021 17:49:49 -0700 (PDT) Reply-To: Sean Christopherson Date: Tue, 30 Mar 2021 17:49:42 -0700 In-Reply-To: <20210331004942.2444916-1-seanjc@google.com> Message-Id: <20210331004942.2444916-3-seanjc@google.com> Mime-Version: 1.0 References: <20210331004942.2444916-1-seanjc@google.com> X-Mailer: git-send-email 2.31.0.291.g576ba9dcdaf-goog Subject: [PATCH 2/2] KVM: x86/mmu: Simplify code for aging SPTEs in TDP MMU From: Sean Christopherson To: Paolo Bonzini Cc: Sean Christopherson , Vitaly Kuznetsov , Wanpeng Li , Jim Mattson , Joerg Roedel , kvm@vger.kernel.org, linux-kernel@vger.kernel.org, Ben Gardon Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Use a basic NOT+AND sequence to clear the Accessed bit in TDP MMU SPTEs, as opposed to the fancy ffs()+clear_bit() logic that was copied from the legacy MMU. The legacy MMU uses clear_bit() because it is operating on the SPTE itself, i.e. clearing needs to be atomic. The TDP MMU operates on a local variable that it later writes to the SPTE, and so doesn't need to be atomic or even resident in memory. Opportunistically drop unnecessary initialization of new_spte, it's guaranteed to be written before being accessed. Using NOT+AND instead of ffs()+clear_bit() reduces the sequence from: 0x0000000000058be6 <+134>: test %rax,%rax 0x0000000000058be9 <+137>: je 0x58bf4 0x0000000000058beb <+139>: test %rax,%rdi 0x0000000000058bee <+142>: je 0x58cdc 0x0000000000058bf4 <+148>: mov %rdi,0x8(%rsp) 0x0000000000058bf9 <+153>: mov $0xffffffff,%edx 0x0000000000058bfe <+158>: bsf %eax,%edx 0x0000000000058c01 <+161>: movslq %edx,%rdx 0x0000000000058c04 <+164>: lock btr %rdx,0x8(%rsp) 0x0000000000058c0b <+171>: mov 0x8(%rsp),%r15 to: 0x0000000000058bdd <+125>: test %rax,%rax 0x0000000000058be0 <+128>: je 0x58beb 0x0000000000058be2 <+130>: test %rax,%r8 0x0000000000058be5 <+133>: je 0x58cc0 0x0000000000058beb <+139>: not %rax 0x0000000000058bee <+142>: and %r8,%rax 0x0000000000058bf1 <+145>: mov %rax,%r15 thus eliminating several memory accesses, including a locked access. Cc: Ben Gardon Signed-off-by: Sean Christopherson --- arch/x86/kvm/mmu/tdp_mmu.c | 5 ++--- 1 file changed, 2 insertions(+), 3 deletions(-) diff --git a/arch/x86/kvm/mmu/tdp_mmu.c b/arch/x86/kvm/mmu/tdp_mmu.c index 724088bea4b0..161b77925a19 100644 --- a/arch/x86/kvm/mmu/tdp_mmu.c +++ b/arch/x86/kvm/mmu/tdp_mmu.c @@ -951,7 +951,7 @@ static int age_gfn_range(struct kvm *kvm, struct kvm_memory_slot *slot, { struct tdp_iter iter; int young = 0; - u64 new_spte = 0; + u64 new_spte; rcu_read_lock(); @@ -966,8 +966,7 @@ static int age_gfn_range(struct kvm *kvm, struct kvm_memory_slot *slot, new_spte = iter.old_spte; if (spte_ad_enabled(new_spte)) { - clear_bit((ffs(shadow_accessed_mask) - 1), - (unsigned long *)&new_spte); + new_spte &= ~shadow_accessed_mask; } else { /* * Capture the dirty status of the page, so that it doesn't get -- 2.31.0.291.g576ba9dcdaf-goog