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 E128CC433F5 for ; Fri, 12 Nov 2021 11:29:25 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id C023260F55 for ; Fri, 12 Nov 2021 11:29:25 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234811AbhKLLcL (ORCPT ); Fri, 12 Nov 2021 06:32:11 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:56340 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233619AbhKLLcL (ORCPT ); Fri, 12 Nov 2021 06:32:11 -0500 Received: from bombadil.infradead.org (bombadil.infradead.org [IPv6:2607:7c80:54:e::133]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id A0EA9C061766 for ; Fri, 12 Nov 2021 03:29:20 -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=F3cRrP1AgMLJj2LL6ZKseeS2xGCQbV9YhyL+BhhxfDs=; b=zxwkL/dIdeT13Z8Di9OS3VYW2b wxNbQpi4NkKoLwP2y2AKoSiKdLdwPhUXQ/D2FLilLz3B8F+ThvikkbDd/OZUpTPwQSJhAZlTywWyE Sju8tE/uKzu+1HBKukGwT6TLJ4pvnoyxO57wPKEHdiBrRtqKG0AjFcpsvLk9/wXSFqeBk0yKoXEo5 c91jF1uB/LS9/S3XBVWRANDe3oG8FcxQoN63g1B24O9oo6ND5MlCkCcc9YDJafcqErocEqL048YsW ZZijt2ekTPG4bd0Hn6d0RV1dd3Sj4MST0Q8dhHtyREdBCWGAvXzmMjxpZKSaE2vUBWUuQKDHfERzd PgvbuKEw==; 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 1mlUk3-00A8w2-Iw; Fri, 12 Nov 2021 11:29:11 +0000 Message-ID: <28435688bab2dc1e272acc02ce92ba9a7589074f.camel@infradead.org> 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 11:29:07 +0000 In-Reply-To: <32b00203-e093-8ffc-a75b-27557b5ee6b1@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> Content-Type: multipart/signed; micalg="sha-256"; protocol="application/pkcs7-signature"; boundary="=-VMrAPuKNR7Iw26WFefsZ" 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 --=-VMrAPuKNR7Iw26WFefsZ Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable On Fri, 2021-11-12 at 11:49 +0100, Paolo Bonzini wrote: > > That would have worked nicely if the MMU notifier could call > > scru_synchronize() on invalidation. Can it kick the vCPU and wait for > > it to exit though? >=20 > Yes, there's kvm_make_all_cpus_request (see=20 > kvm_arch_mmu_notifier_invalidate_range). It can sleep, which is=20 > theoretically wrong---but in practice non-blockable invalidations only= =20 > occur from the OOM reaper, so no CPU can be running. If we care, we can= =20 > return early from kvm_arch_mmu_notifier_invalidate_range for=20 > non-blockable invalidations. OK, so these don't actually want any of that stuff with the rwlock and the invalidation setting the pointer to KVM_UNMAPPED_PAGE that I did in https://lore.kernel.org/kvm/20211101190314.17954-6-dwmw2@infradead.org/ for Xen event channels. It looks like they want their own way of handling it; if the GPA being invalidated matches posted_intr_desc_addr or virtual_apic_page_addr then the MMU notifier just needs to call kvm_make_all_cpus_request() with some suitable checking/WARN magic around the "we will never need to sleep when we shouldn't" assertion that you made above. (And a little bit more thinking about ordering for the case of concurrent invalidation occurring while we are entering the L2 guest, but I think that works out OK.) We *could* use the rwlock thing for steal time reporting, but I still don't really think it's worth doing so. Again, if it was truly going to be a generic mechanism that would solve lots of other problems, I'd be up for it. But if steal time would be the *only* other user of a generic version of the rwlock thing, that just seems like overengineering. I'm still mostly inclined to stand by my original observation that it has a perfectly serviceable HVA that it can use instead. --=-VMrAPuKNR7Iw26WFefsZ Content-Type: application/pkcs7-signature; name="smime.p7s" Content-Disposition: attachment; filename="smime.p7s" Content-Transfer-Encoding: base64 MIAGCSqGSIb3DQEHAqCAMIACAQExDzANBglghkgBZQMEAgEFADCABgkqhkiG9w0BBwEAAKCCECow ggUcMIIEBKADAgECAhEA4rtJSHkq7AnpxKUY8ZlYZjANBgkqhkiG9w0BAQsFADCBlzELMAkGA1UE BhMCR0IxGzAZBgNVBAgTEkdyZWF0ZXIgTWFuY2hlc3RlcjEQMA4GA1UEBxMHU2FsZm9yZDEaMBgG A1UEChMRQ09NT0RPIENBIExpbWl0ZWQxPTA7BgNVBAMTNENPTU9ETyBSU0EgQ2xpZW50IEF1dGhl bnRpY2F0aW9uIGFuZCBTZWN1cmUgRW1haWwgQ0EwHhcNMTkwMTAyMDAwMDAwWhcNMjIwMTAxMjM1 OTU5WjAkMSIwIAYJKoZIhvcNAQkBFhNkd213MkBpbmZyYWRlYWQub3JnMIIBIjANBgkqhkiG9w0B AQEFAAOCAQ8AMIIBCgKCAQEAsv3wObLTCbUA7GJqKj9vHGf+Fa+tpkO+ZRVve9EpNsMsfXhvFpb8 RgL8vD+L133wK6csYoDU7zKiAo92FMUWaY1Hy6HqvVr9oevfTV3xhB5rQO1RHJoAfkvhy+wpjo7Q cXuzkOpibq2YurVStHAiGqAOMGMXhcVGqPuGhcVcVzVUjsvEzAV9Po9K2rpZ52FE4rDkpDK1pBK+ 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