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 mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 92E76C433EF for ; Fri, 12 Nov 2021 15:27:16 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 7915F60ED5 for ; Fri, 12 Nov 2021 15:27:16 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233445AbhKLPaF (ORCPT ); Fri, 12 Nov 2021 10:30:05 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:54836 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232887AbhKLPaC (ORCPT ); Fri, 12 Nov 2021 10:30:02 -0500 Received: from bombadil.infradead.org (bombadil.infradead.org [IPv6:2607:7c80:54:e::133]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 23922C061766 for ; Fri, 12 Nov 2021 07:27:11 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=bombadil.20210309; h=MIME-Version:Content-Type:References: In-Reply-To:Date:Cc:To:From:Subject:Message-ID:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=qnXVD13ONHio3A2VogXepvdymQMZpoyeIZelCm19r3E=; b=oQ/rv0o+NVtfJpQXpaod4Ivc9D BFutr0K7i49wfCkmyMYxvG2E0wEBNZvvMUaAYxM0PPtKI/PGoqUsvZ+6wT17j82W225YHi57cd0HE Ve7bBro6zt3R6f/ZvvCuWIbIZFZgdWWXmtl++AFwFB2zkljZyXcTQ7Iju56lpoGHMKLOpdGOnUkkd FQ9tKa419N/gCdFSablrM27V4MHCcHXKXrS7qUMNkfv525B8RRpj9U2j2W0mc5iZOo3bZV7Nc8OQI ttDv5zF+syS3HpNRqgCBYJEtr+RGL9UjB+8x1Goy4lLafutyHcOgHaL57KsSVy4M5j9t5Oy1pO/wb 1rQ4PX9g==; Received: from [2001:8b0:10b:1::3ae] (helo=u3832b3a9db3152.infradead.org) by bombadil.infradead.org with esmtpsa (Exim 4.94.2 #2 (Red Hat Linux)) id 1mlYSJ-00B4ad-JF; Fri, 12 Nov 2021 15:27:07 +0000 Message-ID: Subject: Re: [PATCH v3] KVM: x86: Fix recording of guest steal time / preempted status From: David Woodhouse To: Paolo Bonzini , kvm Cc: Boris Ostrovsky , Joao Martins , "jmattson@google.com" , "wanpengli@tencent.com" , "seanjc@google.com" , "vkuznets@redhat.com" , "mtosatti@redhat.com" , "joro@8bytes.org" , karahmed@amazon.com Date: Fri, 12 Nov 2021 15:27:04 +0000 In-Reply-To: <7e4b895b-8f36-69cb-10a9-0b4139b9eb79@redhat.com> References: <5d4002373c3ae614cb87b72ba5b7cdc161a0cd46.camel@infradead.org> <4369bbef7f0c2b239da419c917f9a9f2ca6a76f1.camel@infradead.org> <624bc910-1bec-e6dd-b09a-f86dc6cdbef0@redhat.com> <0372987a52b5f43963721b517664830e7e6f1818.camel@infradead.org> <1f326c33-3acf-911a-d1ef-c72f0a570761@redhat.com> <3645b9b889dac6438394194bb5586a46b68d581f.camel@infradead.org> <309f61f7-72fd-06a2-84b4-97dfc3fab587@redhat.com> <96cef64bf7927b6a0af2173b0521032f620551e4.camel@infradead.org> <40d7d808-dce6-a541-18dc-b0c7f4d6586c@redhat.com> <2b400dbb16818da49fb599b9182788ff9896dcda.camel@infradead.org> <32b00203-e093-8ffc-a75b-27557b5ee6b1@redhat.com> <28435688bab2dc1e272acc02ce92ba9a7589074f.camel@infradead.org> <4c37db19-14ed-46b8-eabe-0381ba879e5c@redhat.com> <537fdcc6af80ba6285ae0cdecdb615face25426f.camel@infradead.org> <7e4b895b-8f36-69cb-10a9-0b4139b9eb79@redhat.com> Content-Type: multipart/signed; micalg="sha-256"; protocol="application/pkcs7-signature"; boundary="=-H6IJfII0a5z8a8uS2Xf2" User-Agent: Evolution 3.36.5-0ubuntu1 MIME-Version: 1.0 X-SRS-Rewrite: SMTP reverse-path rewritten from by bombadil.infradead.org. See http://www.infradead.org/rpr.html Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org --=-H6IJfII0a5z8a8uS2Xf2 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable On Fri, 2021-11-12 at 15:56 +0100, Paolo Bonzini wrote: > On 11/12/21 14:28, David Woodhouse wrote: > > A back-to-back write_lock/write_unlock*without* setting the address to > > KVM_UNMAPPED_PAGE? I'm not sure I see how that protects the IRQ > > delivery from accessing the (now stale) physical page after the MMU > > notifier has completed? Not unless it's going to call hva_to_pfn again > > for itself under the read_lock, every time it delivers an IRQ? >=20 > Yeah, you're right, it still has to invalidate it somehow. So > KVM_UNMAPPED_PAGE would go in the hva field of the gfn_to_pfn cache > (merged with kvm_host_map). Or maybe one can use an invalid generation, > too. Right. Or now you have me adding *flags* anyway, so I might just use one of those to mark it invalid. We do need to keep the original hva pointer around to unmap it anyway, even if it's become invalid. That's why my existing code has a separate kvm->arch.xen.shared_info pointer in *addition* to the map->hva pointer; the latter of which *isn't* wiped on invalidation. > > > 2) for memremap/memunmap, all you really care about is reacting to > > > changes in the memslots, so the MMU notifier integration has nothing > > > to do. You still need to call the same hook as > > > kvm_mmu_notifier_invalidate_range() when memslots change, so that > > > the update is done outside atomic context. > >=20 > > Hm, we definitely *do* care about reacting to MMU notifiers in this > > case too. Userspace can do memory overcommit / ballooning etc. > > *without* changing the memslots, and only mmap/munmap/userfault_fd on > > the corresponding HVA ranges. >=20 > Can it do so for VM_IO/VM_PFNMAP memory? 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