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 D375AC77B7A for ; Thu, 25 May 2023 15:54:48 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S241851AbjEYPyr (ORCPT ); Thu, 25 May 2023 11:54:47 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:43956 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S241833AbjEYPyp (ORCPT ); Thu, 25 May 2023 11:54:45 -0400 Received: from mail-yb1-xb4a.google.com (mail-yb1-xb4a.google.com [IPv6:2607:f8b0:4864:20::b4a]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id ADB71E6A for ; Thu, 25 May 2023 08:54:17 -0700 (PDT) Received: by mail-yb1-xb4a.google.com with SMTP id 3f1490d57ef6-bacfa4eefd3so327033276.3 for ; Thu, 25 May 2023 08:54:17 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20221208; t=1685030057; x=1687622057; h=cc:to:from:subject:message-id:references:mime-version:in-reply-to :date:from:to:cc:subject:date:message-id:reply-to; bh=GDMfJuRmq9XZO6/bauwZ7gEniL7UaZKK/szKYWOECa4=; b=uMzuO2hejV9q/GN2+mr53TGXW2G+ALCx8dieU7LqMmMLbcaqzK1NaU8E2yc8PK0igu jFHKEAaHn6USjw1Oht6H19ZSLCERzzjA9yQ5NzU23BgBhevTKU2/RQnclcNfzmjZPRkJ PH0DyeRi8go2kvRzxdXV4sVjXux8EXvzbNTkU0oiVP4oPzOnP9yTyt9YtHpCPDBAyULl hsyGthIPgWmaC2JGf6OYQiQFbeOlj+CJhrllYORLxcMO6/aPCrN7sCa6MNCoaeEa42+1 KMpimxF8pf5qhphDP1fpMcHC5tRUAnhGFoVpjOJH9ozC20ilS6SCH7hRcwJQ84UpFvtS opDw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20221208; t=1685030057; x=1687622057; h=cc:to:from:subject:message-id:references:mime-version:in-reply-to :date:x-gm-message-state:from:to:cc:subject:date:message-id:reply-to; bh=GDMfJuRmq9XZO6/bauwZ7gEniL7UaZKK/szKYWOECa4=; b=cxU9AaAxfb1kXGn44TB/K0Kg7TFm8bSWAyx23QQ7O+DJU4ixdqq7ixK5wKcYgjvpKb mXFrzvG5xxfV1oKphWaaH6Y8nqovyaUBooCQzjBSkAAo5PBBHM48S7JJdsl7UwEixYUp 0NJcYCfekBWBT+BJS9VyYaC9iF/8D5tPFiQ9ukWTOwjhozzFUWdzvI7yu+Olvi2x1Q4d GkrvRHpz2Qt6MaGJJ6dKo0yumzBhSFei36UVNNsgKVdo9PR/BzfLv34D4p1rJmU5lx8H AfQKzbEVw2a+kXcDUKIY7ltJdKU3mujcHGYlcMTA7e+xZHPAf66m6vSBM/rzg0eJjX90 FSrQ== X-Gm-Message-State: AC+VfDwwf69fXx6oDlxd9e5CNzfV9FU+rzBZqQqEN0f1H/No2L6bk7Wx ZD8JLtL+DwPyQD8noAnDjQmCcZUo67E= X-Google-Smtp-Source: ACHHUZ5WNd8rnwxWFJ/9rjJtw4n6PnCBnYKp2t3jItxGv4IVuMiB2nneyF+evn/DmfL4ZExcKzHQYX87Xtg= X-Received: from zagreus.c.googlers.com ([fda3:e722:ac3:cc00:7f:e700:c0a8:5c37]) (user=seanjc job=sendgmr) by 2002:a25:5442:0:b0:ba8:8ab3:3806 with SMTP id i63-20020a255442000000b00ba88ab33806mr2419407ybb.13.1685030056585; Thu, 25 May 2023 08:54:16 -0700 (PDT) Date: Thu, 25 May 2023 08:54:15 -0700 In-Reply-To: Mime-Version: 1.0 References: <20230509134825.1523-1-yan.y.zhao@intel.com> <20230509135006.1604-1-yan.y.zhao@intel.com> Message-ID: Subject: Re: [PATCH v2 1/6] KVM: x86/mmu: add a new mmu zap helper to indicate memtype changes From: Sean Christopherson To: Yan Zhao Cc: Chao Gao , kvm@vger.kernel.org, linux-kernel@vger.kernel.org, pbonzini@redhat.com Content-Type: text/plain; charset="us-ascii" Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org On Thu, May 25, 2023, Yan Zhao wrote: > On Wed, May 24, 2023 at 07:50:24AM -0700, Sean Christopherson wrote: > > bool __kvm_mmu_honors_guest_mtrrs(struct kvm *kvm, bool vm_has_noncoherent_dma); > > > > static inline bool kvm_mmu_honors_guest_mtrrs(struct kvm *kvm) > > { > > > > return __kvm_mmu_honors_guest_mtrrs(kvm, kvm_arch_has_noncoherent_dma(kvm)); > > } > > This should work and it centralizes the comments into one place, though I dislike > having to pass true as vm_has_noncoherent_dma in case of 1->0 transition. :) Yeah, I don't love it either, but the whole 1=>0 transition is awkward. FWIW, KVM doesn't strictly need to zap in that case since the guest isn't relying on WB for functionality, i.e. we could just skip it. > > > diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c > > > index 41d7bb51a297..ad0c43d7f532 100644 > > > --- a/arch/x86/kvm/x86.c > > > +++ b/arch/x86/kvm/x86.c > > > @@ -13146,13 +13146,19 @@ EXPORT_SYMBOL_GPL(kvm_arch_has_assigned_device); > > > > > > void kvm_arch_register_noncoherent_dma(struct kvm *kvm) > > > { > > > - atomic_inc(&kvm->arch.noncoherent_dma_count); > > > + if (atomic_inc_return(&kvm->arch.noncoherent_dma_count) == 1) { > > > + if (kvm_mmu_cap_honors_guest_mtrrs(kvm)) > > > + kvm_zap_gfn_range(kvm, 0, ~0ULL); > > > > No need for multiple if statements. Though rather than have identical code in > > both the start/end paths, how about this? That provides a single location for a > > comment. Or maybe first/last instead of start/end? > > > > static void kvm_noncoherent_dma_start_or_end(struct kvm *kvm) > What does start_or_end or first_or_last stand for? Start/End of device (un)assignment, or First/Last device (un)assigned. Definitely feel free to pick a better name.