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 X-Spam-Level: X-Spam-Status: No, score=-7.2 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_2 autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 98BDEC63798 for ; Thu, 26 Nov 2020 21:48:45 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id C962020DD4 for ; Thu, 26 Nov 2020 21:48:44 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="QWrduoIm" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2387747AbgKZVso (ORCPT ); Thu, 26 Nov 2020 16:48:44 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:49200 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726178AbgKZVsn (ORCPT ); Thu, 26 Nov 2020 16:48:43 -0500 Received: from merlin.infradead.org (merlin.infradead.org [IPv6:2001:8b0:10b:1231::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 7525EC0613D4 for ; Thu, 26 Nov 2020 13:48:43 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=merlin.20170209; 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=2NxskwwXj6JKO6WeYrz+qbTBn3wJ/RAiu2A7wUf1Cik=; b=QWrduoImx9XhhSRvZmzDMATE3J ReS/bg+rt2wjcUupVwQz38ZCfUevsmrFxs2Y7CdFjR4Q+J4dhXbw1iLsgQ550zEiFVIt/GR5XUfW/ AdSJfZke8ge0f7iuGqQLYlTpwWSdRbOju277Wj48OxsZVGuXuOXPMg7+mExG8bu+j4ItGE2QcgNDH nYCMJ96sV+/Fh2W5JPSzFlcd9yqwOclpe20w1YrDMWx84AudbEA1/w9O63JMpF1Nmn6yuDwGrXlJF M23K0Tk5cXceN9qsGIDV59E/Cvt4N4PimSQp+dpSP3ipI6W7LA6SFrJ2baY0qYVkjMXOurpHkQqj4 AgaQvd2w==; Received: from [54.239.6.185] (helo=freeip.amazon.com) by merlin.infradead.org with esmtpsa (Exim 4.92.3 #3 (Red Hat Linux)) id 1kiP7w-00047k-Ok; Thu, 26 Nov 2020 21:48:33 +0000 Message-ID: <6e7060415fe321a3969a76330b643116a5ab44d1.camel@infradead.org> Subject: Re: [RFC PATCH] Fix split-irqchip vs interrupt injection window request. From: David Woodhouse To: Paolo Bonzini , Sean Christopherson , "Borghorst, Hendrik" Cc: kvm , "Sironi, Filippo" , "Raslan, KarimAllah" , Matt Gingell , Steve Rutherford , liran@amazon.com Date: Thu, 26 Nov 2020 21:48:29 +0000 In-Reply-To: <26940473-6bd0-fc2b-f9bd-35a6a502baff@redhat.com> References: <62918f65ec78f8990278a6a0db0567968fa23e49.camel@infradead.org> <017de9019136b5d2ec34132b96b9f0273c21d6f1.camel@infradead.org> <20201125211955.GA450871@google.com> <99a9c1dfbb21744e5081d924291d3b09ab055813.camel@infradead.org> <95c0c9a01ea9692b3b18ac677d7e7c6e7636bfe4.camel@infradead.org> <26940473-6bd0-fc2b-f9bd-35a6a502baff@redhat.com> Content-Type: multipart/signed; micalg="sha-256"; protocol="application/x-pkcs7-signature"; boundary="=-WOR6iS0swi94ZaHTsdj2" X-Mailer: Evolution 3.28.5-0ubuntu0.18.04.2 Mime-Version: 1.0 X-SRS-Rewrite: SMTP reverse-path rewritten from by merlin.infradead.org. See http://www.infradead.org/rpr.html Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org --=-WOR6iS0swi94ZaHTsdj2 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable On Thu, 2020-11-26 at 18:59 +0100, Paolo Bonzini wrote: > On 26/11/20 18:29, David Woodhouse wrote: > > On Thu, 2020-11-26 at 11:10 +0000, David Woodhouse wrote: > > >=20 > > > > whether or not there's an IRQ in the > > > > LAPIC should be irrelevant when deciding to exit to userspace. Not= e, the > > > > reinjection check covers vcpu->arch.interrupt.injected for the case= where LAPIC > > > > is in userspace. > > > >=20 > > > > return kvm_arch_interrupt_allowed(vcpu) && > > > > (!lapic_in_kernel(vcpu) || !kvm_cpu_has_extint(vcp= u)) && > > > > !kvm_event_needs_reinjection(vcpu) && > > > > kvm_cpu_accept_dm_intr(vcpu); > > > > } > > >=20 > > > Makes sense. I'm putting this version through some testing and will > > > post it later... > >=20 > > Hm, that survived enough test iterations to persuade me to post it, but > > then seems to have fallen over later. I'm reverting to the > > kvm_cpu_has_injectable_intr() version to leave that one running too and > > be sure it's gone in that. FWIW I've just reproduced that hang on one of the iterations *without* "noapic" on its command line at all; this one was just with 'clearcpuid=3D450'. That's clearing the ARAT bit to force it to use the HPET+MSI for timers. The earlier one that had failed was 'noapic clearcpuid=3D450'. So that one looks like a separate bug, and I get to go frown at our HPET emulation instead. It probably wasn't a failure of the fix we're looking at here. I'm going to go and check if I can reproduce that even with the in- kernel irqchip mode, and claim it's someone else's problem for now :) > !kvm_cpu_has_injectable_intr(vcpu) boils down (assuming no nested virt) t= o >=20 > if (!lapic_in_kernel(v)) > return !v->arch.interrupt.injected; >=20 > if (kvm_cpu_has_extint(v)) > return 0; >=20 > return 1; >=20 > and Sean's proposal instead is the same indeed (the first "if" doesn't= =20 > matter), so there may be more than one bug. >=20 > But it turns out that with some more inlining and Boolean algebra, we=20 > can actually figure out what the code does. :) I had just finished=20 > writing a looong review of your patch starting from that idea, so I'll= =20 > post it. Neat. Your version, once I made it build, ought to be functionally identical to the one I posted; just a bit neater. Although I do kind of like the symmetry of my original version using kvm_cpu_has_injectable_intr(), which is the condition used in vcpu_enter_guest() for enabling the interrupt window vmexit in the first place. It makes sense for those to match. We enable the irq window if kvm_cpu_has_injectable_intr() or if userspace asks. And when the exit happens, we feed it to userspace unless kvm_cpu_has_injectable_intr(). If we go with your simpler version, I wonder if it makes sense to make similar changes to the conditions in vcpu_enter_guest() to make it clearer that they match? --=-WOR6iS0swi94ZaHTsdj2 Content-Type: application/x-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 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