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 1F85DC433EF for ; Sat, 20 Nov 2021 04:53:13 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S236533AbhKTE4M (ORCPT ); Fri, 19 Nov 2021 23:56:12 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:54978 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S236230AbhKTEym (ORCPT ); Fri, 19 Nov 2021 23:54:42 -0500 Received: from mail-pl1-x64a.google.com (mail-pl1-x64a.google.com [IPv6:2607:f8b0:4864:20::64a]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id E10FCC0613FD for ; Fri, 19 Nov 2021 20:51:05 -0800 (PST) Received: by mail-pl1-x64a.google.com with SMTP id p16-20020a170902e75000b0014271728fd6so5699916plf.18 for ; Fri, 19 Nov 2021 20:51:05 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20210112; h=reply-to:date:in-reply-to:message-id:mime-version:references :subject:from:to:cc; bh=MH2AUHVRIZhtROi1wUUoi6p64S7AM5UJwN9jo7kK5K4=; b=HEAD2MGrJh1JZxqAXwtHth0dcTykme8tJfJVnbHH9ARwbHpPa6bI89XSMrWgypcvWs 4ZMSLRGthF9dbN/v8+bh/hwwm1iwI8yHxP5Qyuz7QShTYivvH2VFSUkRLi6fYUkVOCgu rIpCm1cQOkuaIvLm9y/qtbIe3c3ws1JhtX0QJjtBqo8nD4eKE6pHS3T979iRhZnP+YoE CrxkDsVJHQvTTIR/SDZQ++lWXBeyY8FFcMDz8+ZnwhPLMrVVrHSppLtosLO03ADV700K uqobkZ9AN0fNPTzulf4uKPlEFmW3fd19aYxMU99QkISBOioTV5gSnlG8FlzL0Q3VeRJ4 BOSA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:reply-to:date:in-reply-to:message-id :mime-version:references:subject:from:to:cc; bh=MH2AUHVRIZhtROi1wUUoi6p64S7AM5UJwN9jo7kK5K4=; b=BzXhCmoF5duqsiLplq98FbL8OeYMkU/llmVYaunYSWkGPf0kckX617G/LOBgSnLDLg cyHoQy1+KfsQ5ZWYz5VXgZ85EfF7A9sx25RCwH/kOivvtJWjklvZ6AaMrPz7UHisQbL4 GO/KhfeQlwJUIK7Rq5xSeelhRKBINJUCTGGo//SQGej7iF1Vj1s0XMSp8sS4YRiOnMQg 4Q0Uzb/qHvqNisyMx7Wq9A8sFMOReYlwouFcYcOymyxhQMplMZaLhDHoqxQsyiRKtHEk 53CroSTiyPn8bw6OwttDuD/AoNhYNBGoPiFQZ/qaA6M+/AWCsyfWlwAZ28yweRT4Uwo2 GHRQ== X-Gm-Message-State: AOAM533uqzv2BR6p0Z6X6AHSwacSsBTbtFElRrnX6iFc6MPUkt/CwfWt KYzB2ByiG7Vf5hHItmkWqhiuQJ6KWwA= X-Google-Smtp-Source: ABdhPJwkXsHa1ZxWg33eTBjj65cC+yUKS21/OClqJHqBL3Lo/EIK+5K+Z5udYfgnQan4eUH1w7c4a0lyBjY= X-Received: from seanjc.c.googlers.com ([fda3:e722:ac3:cc00:7f:e700:c0a8:3e5]) (user=seanjc job=sendgmr) by 2002:a17:903:1103:b0:143:a593:dc41 with SMTP id n3-20020a170903110300b00143a593dc41mr83678976plh.5.1637383865389; Fri, 19 Nov 2021 20:51:05 -0800 (PST) Reply-To: Sean Christopherson Date: Sat, 20 Nov 2021 04:50:25 +0000 In-Reply-To: <20211120045046.3940942-1-seanjc@google.com> Message-Id: <20211120045046.3940942-8-seanjc@google.com> Mime-Version: 1.0 References: <20211120045046.3940942-1-seanjc@google.com> X-Mailer: git-send-email 2.34.0.rc2.393.gf8c9666880-goog Subject: [PATCH 07/28] KVM: x86/mmu: Document that zapping invalidated roots doesn't need to flush 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, Hou Wenlong , Ben Gardon Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org Remove the misleading flush "handling" when zapping invalidated TDP MMU roots, and document that flushing is unnecessary for all flavors of MMUs when zapping invalid/obsolete roots/pages. The "handling" in the TDP MMU is dead code, as zap_gfn_range() is called with shared=true, in which case it will never return true due to the flushing being handled by tdp_mmu_zap_spte_atomic(). No functional change intended. Signed-off-by: Sean Christopherson --- arch/x86/kvm/mmu/mmu.c | 10 +++++++--- arch/x86/kvm/mmu/tdp_mmu.c | 15 ++++++++++----- 2 files changed, 17 insertions(+), 8 deletions(-) diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c index 3adac2630c4c..e00e46205730 100644 --- a/arch/x86/kvm/mmu/mmu.c +++ b/arch/x86/kvm/mmu/mmu.c @@ -5642,9 +5642,13 @@ static void kvm_zap_obsolete_pages(struct kvm *kvm) } /* - * Trigger a remote TLB flush before freeing the page tables to ensure - * KVM is not in the middle of a lockless shadow page table walk, which - * may reference the pages. + * Kick all vCPUs (via remote TLB flush) before freeing the page tables + * to ensure KVM is not in the middle of a lockless shadow page table + * walk, which may reference the pages. The remote TLB flush itself is + * not required and is simply a convenient way to kick vCPUs as needed. + * KVM performs a local TLB flush when allocating a new root (see + * kvm_mmu_load()), and the reload in the caller ensure no vCPUs are + * running with an obsolete MMU. */ kvm_mmu_commit_zap_page(kvm, &kvm->arch.zapped_obsolete_pages); } diff --git a/arch/x86/kvm/mmu/tdp_mmu.c b/arch/x86/kvm/mmu/tdp_mmu.c index 981fb0517384..4305ee8e3de3 100644 --- a/arch/x86/kvm/mmu/tdp_mmu.c +++ b/arch/x86/kvm/mmu/tdp_mmu.c @@ -833,7 +833,6 @@ void kvm_tdp_mmu_zap_invalidated_roots(struct kvm *kvm) { struct kvm_mmu_page *next_root; struct kvm_mmu_page *root; - bool flush = false; lockdep_assert_held_read(&kvm->mmu_lock); @@ -846,7 +845,16 @@ void kvm_tdp_mmu_zap_invalidated_roots(struct kvm *kvm) rcu_read_unlock(); - flush = zap_gfn_range(kvm, root, 0, -1ull, true, flush, true); + /* + * A TLB flush is unnecessary, invalidated roots are guaranteed + * to be unreachable by the guest (see kvm_tdp_mmu_put_root() + * for more details), and unlike the legacy MMU, no vCPU kick + * is needed to play nice with lockless shadow walks as the TDP + * MMU protects its paging structures via RCU. Note, zapping + * will still flush on yield, but that's a minor performance + * blip and not a functional issue. + */ + (void)zap_gfn_range(kvm, root, 0, -1ull, true, false, true); /* * Put the reference acquired in @@ -860,9 +868,6 @@ void kvm_tdp_mmu_zap_invalidated_roots(struct kvm *kvm) } rcu_read_unlock(); - - if (flush) - kvm_flush_remote_tlbs(kvm); } /* -- 2.34.0.rc2.393.gf8c9666880-goog