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 0A204C46CA1 for ; Mon, 18 Sep 2023 18:08:03 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229617AbjIRSIG (ORCPT ); Mon, 18 Sep 2023 14:08:06 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:50204 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229497AbjIRSIF (ORCPT ); Mon, 18 Sep 2023 14:08:05 -0400 Received: from mail-yw1-x1149.google.com (mail-yw1-x1149.google.com [IPv6:2607:f8b0:4864:20::1149]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 7F96C11C for ; Mon, 18 Sep 2023 11:07:47 -0700 (PDT) Received: by mail-yw1-x1149.google.com with SMTP id 00721157ae682-59b5d4a8242so57946097b3.0 for ; Mon, 18 Sep 2023 11:07:47 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20230601; t=1695060466; x=1695665266; darn=vger.kernel.org; h=cc:to:from:subject:message-id:references:mime-version:in-reply-to :date:from:to:cc:subject:date:message-id:reply-to; bh=GmTnJV1ADdgeWLSdVtD0/++n9rF2F3zpNnWnlLAWBfc=; b=GgolAgTXkgd3VIcWP7ez1fL2XXc6EffJ/lZHJY+CaZmD4jVSs7DGfqajEaHeJcUNuW FkavDT6fVgLVQ5xkOGOJJnVLtWhrkkxlS1HxNL7qqHmZ/kzCz7vnHVdVkg9MKC3dEG73 AOoTgxwQoGiOaYTgW43KnWApZ6N8oLXKjkaxD+mQ+tTSSvG31kNCNO8kTIXcrmPfJ3ZF 1ObEDp++U8gHy1Ik4SdqWwJVtkmv3UCUicQmXjiJ/R8Ruxmjfu/qsZ4Sd7gxI/ix0M2D j67xIjfUbFDe2nJWRSUpW5FDCfcr3Cq1FFFQDtTEi2uBnbDtJD6OHIzX2wn+zgy5S8IK IQLQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1695060466; x=1695665266; 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=GmTnJV1ADdgeWLSdVtD0/++n9rF2F3zpNnWnlLAWBfc=; b=aOyRyydvRYS2CvOU2/RywlmdWGYAXv4sdO2H7IsphIGyb/ve5F1Xtrn3uWaXjshTZW X08yQHLIieuk7z9B1Q8pIHNX+S3zbpitTNDFbsekw+G9n6R+/t0ZnYov8uSV2O1zv4At Yxb2zHEFHt+tCUKQHMcdLrVx72ShH09RtRz5atOjelzsXvajY2o7y22gQg21H+onLAEe geG+jLPQyHgNTWz8BkUFKaG9cSYzkQx0XDrnm6I7igxoUqs8N/GqCF7YRHzUg5KxhfTM GneG02MaF6BlGb6jyjGBdaa+Q1VemwVGf0X09YoMNEdFSl4JoF7v3cEdmzP2G2LyeKkM qWcg== X-Gm-Message-State: AOJu0Yz3vFQ0ucBtSFBroL4X8Qovuimo+pUX9zVSYaVSR2iEZgFG0evc aGnhyH3vCddRVWlJMMubAt7kTAwxfT4= X-Google-Smtp-Source: AGHT+IEq7OsCrz76V3mWe/TIshYEHjDRsyEPSR2V+8pZ5m5ogKwdrddivlWbUzqfoZQCwHuHP6FyJ33Wqu8= X-Received: from zagreus.c.googlers.com ([fda3:e722:ac3:cc00:7f:e700:c0a8:5c37]) (user=seanjc job=sendgmr) by 2002:a81:af28:0:b0:584:3d8f:a425 with SMTP id n40-20020a81af28000000b005843d8fa425mr264367ywh.10.1695060466507; Mon, 18 Sep 2023 11:07:46 -0700 (PDT) Date: Mon, 18 Sep 2023 11:07:44 -0700 In-Reply-To: Mime-Version: 1.0 References: Message-ID: Subject: Re: KVM nonblocking MMU notifier with KVM_GUEST_USES_PFN looks racy [but is currently unused] From: Sean Christopherson To: Jann Horn Cc: Paolo Bonzini , David Woodhouse , kernel list , KVM list , Linux-MM , Michal Hocko Content-Type: text/plain; charset="us-ascii" Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org On Mon, Sep 18, 2023, Jann Horn wrote: > Hi! > > I haven't tested this and might be missing something, but I think that > the MMU notifier for KVM_GUEST_USES_PFN pfncache is currently a bit > broken. Except that nothing seems to actually use KVM_GUEST_USES_PFN, > so currently it's not actually a problem? Yeah, the implementation is busted, and IMO the entire concept is a dead-end[1]. David Steven's series[2] doesn't actually rip out KVM_GUEST_USES_PFN, I'll add that to the todo list. There are no users, and I don't expect any to come along, precisely because it's busted :-) [1] https://lore.kernel.org/all/ZBEEQtmtNPaEqU1i@google.com [2] https://lkml.kernel.org/r/20230911021637.1941096-1-stevensd%40google.com