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=-5.3 required=3.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED,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 3080FC433DF for ; Fri, 14 Aug 2020 14:14:32 +0000 (UTC) Received: from lists.xenproject.org (lists.xenproject.org [192.237.175.120]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id F3C9020866 for ; Fri, 14 Aug 2020 14:14:31 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="gcYd/8PP" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org F3C9020866 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=infradead.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=xen-devel-bounces@lists.xenproject.org Received: from localhost ([127.0.0.1] helo=lists.xenproject.org) by lists.xenproject.org with esmtp (Exim 4.92) (envelope-from ) id 1k6aT7-0001Qe-HP; Fri, 14 Aug 2020 14:14:05 +0000 Received: from us1-rack-iad1.inumbo.com ([172.99.69.81]) by lists.xenproject.org with esmtp (Exim 4.92) (envelope-from ) id 1k6aT5-0001QZ-HD for xen-devel@lists.xenproject.org; Fri, 14 Aug 2020 14:14:04 +0000 X-Inumbo-ID: 91c05911-af9d-4a53-8283-bf705358506a Received: from merlin.infradead.org (unknown [2001:8b0:10b:1231::1]) by us1-rack-iad1.inumbo.com (Halon) with ESMTPS id 91c05911-af9d-4a53-8283-bf705358506a; Fri, 14 Aug 2020 14:14:01 +0000 (UTC) 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=CfIj3x2vL5eBfQB1HcjPWo5BFeX/jcwSWoYS+6IhKzA=; b=gcYd/8PPyHYcppVnTaZ9tkTpqC MlE6ZfCrR1Z/6EUpCTolYz8eimUYhYTrpWKIZPVmEp778HJzP8MuzWTE3Q1u3/1SViATrddSCH1U5 QRH1n5uq6/2K5tlK3NowNrgpT+Jl0JHHXUPqPBvBrY0fAa9N2LJOtTK+AsDVDfVV9dl+oDr/xVi+b XoHzyg2oatKFKxSQYmutSCBColVrAeGEWGSoq3l3sC0b+T5Ne4WEKMnHVh40xt0KxV/TETvHegQLm Lc7fJakdHtx86uuaWegUh7cJSMwd4SZzU9uUL7Y9NhBisI2bn2vbsCnekzR7Ear5zl/lKu+3nLLUf /v2KnPRA==; Received: from 54-240-197-230.amazon.com ([54.240.197.230] helo=freeip.amazon.com) by merlin.infradead.org with esmtpsa (Exim 4.92.3 #3 (Red Hat Linux)) id 1k6aSv-0006py-CQ; Fri, 14 Aug 2020 14:13:53 +0000 Message-ID: <999f185404fcedc03d8cf1bd1f47a492219b8e9b.camel@infradead.org> Subject: Re: [Xen-devel] [PATCH v2] x86/hvm: re-work viridian APIC assist code From: David Woodhouse To: Roger Pau =?ISO-8859-1?Q?Monn=E9?= , paul@xen.org Cc: xen-devel@lists.xenproject.org, 'Eslam Elnikety' , 'Andrew Cooper' , 'Shan Haitao' , 'Jan Beulich' Date: Fri, 14 Aug 2020 15:13:51 +0100 In-Reply-To: <20200813094555.GF975@Air-de-Roger> References: <20180118151059.1336-1-paul.durrant@citrix.com> <1535153880.24926.28.camel@infradead.org> <7547be305e3ede9edb897e2be898fe54e0b4065c.camel@infradead.org> <002d01d67149$37404b00$a5c0e100$@xen.org> <20200813094555.GF975@Air-de-Roger> Content-Type: multipart/signed; micalg="sha-256"; protocol="application/x-pkcs7-signature"; boundary="=-vIdiQ002Xf9wMKagiTMP" 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 X-BeenThere: xen-devel@lists.xenproject.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Xen developer discussion List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Errors-To: xen-devel-bounces@lists.xenproject.org Sender: "Xen-devel" --=-vIdiQ002Xf9wMKagiTMP Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable On Thu, 2020-08-13 at 11:45 +0200, Roger Pau Monn=C3=A9 wrote: > > The loop appears to be there to handle the case where multiple > > devices assigned to a domain have MSIs programmed with the same > > dest/vector... which seems like an odd thing for a guest to do but I > > guess it is at liberty to do it. Does it matter whether they are > > maskable or not? >=20 > Such configuration would never work properly, as lapic vectors are > edge triggered and thus can't be safely shared between devices? >=20 > I think the iteration is there in order to get the hvm_pirq_dpci > struct that injected that specific vector, so that you can perform the > ack if required. Having lapic EOI callbacks should simply this, as you > can pass a hvm_pirq_dpci when injecting a vector, and that would be > forwarded to the EOI callback, so there should be no need to iterate > over the list of hvm_pirq_dpci for a domain. If we didn't have the loop =E2=80=94 or more to the point if we didn't grab= the domain-global d->event_lock that protects it =E2=80=94 then I wouldn't even care about optimising the whole thing away for the modern MSI case. It isn't the act of not doing any work in the _hvm_dpci_msi_eoi() function that takes the time. It's that domain-global lock, and a little bit the retpoline-stalled indirect call from pt_pirq_interate(). I suppose with Roger's series, we'll still suffer the retpoline stall for a callback that ultimately does nothing, but it's nowhere near as expensive as the lock. --=-vIdiQ002Xf9wMKagiTMP 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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