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 E4902C71150 for ; Fri, 18 Aug 2023 13:48:32 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S239615AbjHRNsC (ORCPT ); Fri, 18 Aug 2023 09:48:02 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:58762 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1377369AbjHRNri (ORCPT ); Fri, 18 Aug 2023 09:47:38 -0400 Received: from mail-pg1-x549.google.com (mail-pg1-x549.google.com [IPv6:2607:f8b0:4864:20::549]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 3A6194218 for ; Fri, 18 Aug 2023 06:46:55 -0700 (PDT) Received: by mail-pg1-x549.google.com with SMTP id 41be03b00d2f7-55c7d9edd16so1237858a12.1 for ; Fri, 18 Aug 2023 06:46:55 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20221208; t=1692366389; x=1692971189; h=cc:to:from:subject:message-id:references:mime-version:in-reply-to :date:from:to:cc:subject:date:message-id:reply-to; bh=jNlR4KxrzE72vpNuTyvfyVvbrBWXFgdYpu7h9tDZYwU=; b=vtgMMSNPRqRJdWk7DyvvesFPY2OKKk3Wr7T5UwkfgFFO5g1QQJFjlFXnDFSHqiiEhe lD1aF4LgRzwD94FWX/Pz6c0u5HK7icnntQ1CaUHS9vHM9IfBLQRx/IMRnqrJ2XvhouId 0Moq9CjzTasCUtU+i24RHqrDECGkg8c4HxeYW+3hVVSOqSMUWJWhjsUvHOJDfm1QKkX6 RjHcybduEWy7snz7CQD66T2zmTu38UEDu/nBqhGMu91SIcVhwqvGGoeO5Bpr4NZT3IDo iT5uJvB/M1Eiu/YSbP5jaRC7KPWjfci5ugAcpMnSVIZdcBjjnH/rWontMjdvVjfSl3nK j/Sg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20221208; t=1692366389; x=1692971189; 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=jNlR4KxrzE72vpNuTyvfyVvbrBWXFgdYpu7h9tDZYwU=; b=WMefzqfxzR2A6pZ8P6yizcTKjfy1Np/urwK+HIon9877rpudHf1UXGMWQbNS8HTDqg JBs1QOFP0ea63AtVZ3pYKDDH6KdgNJk0NZHKQunx+jDxXGxMGQUu09sNeX4gPTIKIHKA IJph5jrO/3R1mMRJ0deBaXLZKDf+XhqBuqEb84jTT3P/xWDFcVL68HZD7qbXAztEY67k K149U72Y67So4mqgI9aAWlz/pwf0QnBkdMP6Wplytm4nQtyXUtgy0wWeUX2/kK8sA01K 8UviDLnqjPKi1esE3gKoKcdMX1gcMxdLbLcBCGTy9h29rKbyu1P713/og+qU7IJGoSPs +RqQ== X-Gm-Message-State: AOJu0YzEvCQXFny8tKF2aWO9vBSTZBpf2UtqImk0qF8ZDjqT8XMLTMLk YK3x8Efse08S69E7DbN5eHddnIvE0HU= X-Google-Smtp-Source: AGHT+IFmESdYKpgGUbBQHEYsCSENkDJqn8Y0SDC8FdMY70toMQGagfsR2ZiXJMY8GWX5/b2Nj3MnFnTrH+0= X-Received: from zagreus.c.googlers.com ([fda3:e722:ac3:cc00:7f:e700:c0a8:5c37]) (user=seanjc job=sendgmr) by 2002:a63:7b10:0:b0:565:eb0b:6daf with SMTP id w16-20020a637b10000000b00565eb0b6dafmr443690pgc.7.1692366388693; Fri, 18 Aug 2023 06:46:28 -0700 (PDT) Date: Fri, 18 Aug 2023 06:46:26 -0700 In-Reply-To: Mime-Version: 1.0 References: <20230808085056.14644-1-yan.y.zhao@intel.com> Message-ID: Subject: Re: [PATCH 0/2] KVM: x86/mmu: .change_pte() optimization in TDP MMU From: Sean Christopherson To: Yan Zhao Cc: 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: linux-kernel@vger.kernel.org On Fri, Aug 18, 2023, Yan Zhao wrote: > On Thu, Aug 17, 2023 at 10:53:25AM -0700, Sean Christopherson wrote: > > And FWIW, removing .change_pte() entirely, even without any other optimizations, > > will also benefit those guests, as it will remove a source of mmu_lock contention > > along with all of the overhead of invoking callbacks, walking memslots, etc. And > > removing .change_pte() will benefit *all* guests by eliminating unrelated callbacks, > > i.e. callbacks when memory for the VMM takes a CoW fault. > > > If with above "always write_fault = true" solution, I think it's better. Another option would be to allow a per-mm override of use_zero_page, but I think I like the KVM memslot route more as it provides better granularity, doesn't prevent CoW for VMM memory, and works even if THP isn't being used.