From nobody Sun Feb 8 23:26:53 2026 Received: from desiato.infradead.org (desiato.infradead.org [90.155.92.199]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 7344A1E4BE; Thu, 8 May 2025 20:30:19 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=90.155.92.199 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1746736223; cv=none; b=TDG0YnYUeHsenAVMuSuoVZBqgxFy+afHsq96k8yV/rY+9yNAR1/gQFwAgQAaG/0QDxGpND+kLfrZCU/kbW/SxZVPEpiRRLbwoDXeH0gXfY+l69P9a6viOEBnt9Tj++twV8GEIUAlz5HezNE6+YsWwiZEVRdvbz2rcEUDgVrmvc0= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1746736223; c=relaxed/simple; bh=EZf2OJkwOgg3s3KXPEbm0/OKkVOnsT+pfG7EyuQohjc=; h=Message-ID:Subject:From:To:Cc:Date:Content-Type:MIME-Version; b=gAiwEP/Ut2tepY4JzMRl2bTQoLJ5IurdVkqzu9UEU+mR8dOM4KdJpmNp/8Z6FY119PEyppliaOhtFUFpvUavaf3P5wfr2SlBMG3pc+dCrHERVd93N+8VgSVrBtj9JmNty9pVsyKHzdKPYn65edlGAtHjDikR/fUOWrOCvilcMYU= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=infradead.org; spf=none smtp.mailfrom=desiato.srs.infradead.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b=C4D9C+bS; arc=none smtp.client-ip=90.155.92.199 Authentication-Results: smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=infradead.org Authentication-Results: smtp.subspace.kernel.org; spf=none smtp.mailfrom=desiato.srs.infradead.org Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="C4D9C+bS" DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=desiato.20200630; h=MIME-Version:Content-Type:Date:Cc:To: From:Subject:Message-ID:Sender:Reply-To:Content-Transfer-Encoding:Content-ID: Content-Description:In-Reply-To:References; bh=kKIsRBztNYxYvEBf8AR/cHudZh+YcvoLcKwaUbZP9aM=; b=C4D9C+bSVwSBJjOqcQFuqLVvkG iqOeMmzt4D8iI/hypmN4qjQYZp6vouq9WERl3HyzR9S+4hjF5+7/nQtPSELzDxmlQYuhg2PDz8nZi gzXRklSeLRtLqSUyzIDMCJvp/M6/G34SWPGmfdkhT8GYFH7j9DV4amZ4oa0JqtusvVt32/K7E6p0Y 2GUq9EkVa8iw7chUuTe7rqu5hR6ufSAE6Bvtc0TYrdXCKXtl2+V1Eg4nJHrMCc3/K/dOQpKZi9N24 j54m2XViMA/h2zeAxTdNwPm/E+wBXoteSu2xvC1tg85kocu1LCtELbpculjBH1hajp55aRcr4/8D5 LlMvNxVQ==; Received: from 67-130-182-136.dia.static.qwest.net ([67.130.182.136] helo=freeip.amazon.com) by desiato.infradead.org with esmtpsa (Exim 4.98.1 #2 (Red Hat Linux)) id 1uD7sm-0000000G9zu-2YQT; Thu, 08 May 2025 20:30:17 +0000 Message-ID: Subject: KVM: x86/xen: Allow 'out of range' event channel ports in IRQ routing table. From: David Woodhouse To: kvm@vger.kernel.org, Sean Christopherson , "Orlov, Ivan" Cc: Paul Durrant , Paolo Bonzini , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , x86@kernel.org, "H. Peter Anvin" , linux-kernel@vger.kernel.org Date: Thu, 08 May 2025 13:30:12 -0700 Content-Type: multipart/signed; micalg="sha-256"; protocol="application/pkcs7-signature"; boundary="=-3a6t3PAWEYOsTNK0Xr8Z" User-Agent: Evolution 3.52.3-0ubuntu1 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-SRS-Rewrite: SMTP reverse-path rewritten from by desiato.infradead.org. See http://www.infradead.org/rpr.html --=-3a6t3PAWEYOsTNK0Xr8Z Content-Transfer-Encoding: quoted-printable MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" From: David Woodhouse To avoid imposing an ordering constraint on userspace, allow 'invalid' event channel targets to be configured in the IRQ routing table. This is the same as accepting interrupts targeted at vCPUs which don't exist yet, which is already the case for both Xen event channels *and* for MSIs (which don't do any filtering of permitted APIC ID targets at all). If userspace actually *triggers* an IRQ with an invalid target, that will fail cleanly, as kvm_xen_set_evtchn_fast() also does the same range check. If KVM enforced that the IRQ target must be valid at the time it is *configured*, that would force userspace to create all vCPUs and do various other parts of setup (in this case, setting the Xen long_mode) before restoring the IRQ table. Cc: stable@vger.kernel.org Signed-off-by: David Woodhouse Reviewed-by: Paul Durrant --- arch/x86/kvm/xen.c | 14 ++++++++++++-- 1 file changed, 12 insertions(+), 2 deletions(-) diff --git a/arch/x86/kvm/xen.c b/arch/x86/kvm/xen.c index 38b33cdd4232..2a593db2ea3f 100644 --- a/arch/x86/kvm/xen.c +++ b/arch/x86/kvm/xen.c @@ -1970,8 +1970,18 @@ int kvm_xen_setup_evtchn(struct kvm *kvm, { struct kvm_vcpu *vcpu; =20 - if (ue->u.xen_evtchn.port >=3D max_evtchn_port(kvm)) - return -EINVAL; + /* + * No check for being within range of max_evtchn_port() here. + * Userspace can configure what ever targets it likes; they + * just won't be delivered if/while they're invalid. Just like + * userspace can configure MSIs which target non-existent APICs. + * This means that on Live Migration and Live Update, the IRQ + * routing table and be restored *independently* of other things + * like creating vCPUs without imposing an ordering dependency on + * userspace. In this particular case, the problematic ordering + * would be with setting the Xen 'long mode' flag which changes + * max_evtchn_port() to allow 4096 instead of 1024 event channels. + */ =20 /* We only support 2 level event channels for now */ if (ue->u.xen_evtchn.priority !=3D KVM_IRQ_ROUTING_XEN_EVTCHN_PRIO_2LEVEL) --=20 2.49.0 --=-3a6t3PAWEYOsTNK0Xr8Z Content-Type: application/pkcs7-signature; name="smime.p7s" Content-Disposition: attachment; filename="smime.p7s" Content-Transfer-Encoding: base64 MIAGCSqGSIb3DQEHAqCAMIACAQExDzANBglghkgBZQMEAgEFADCABgkqhkiG9w0BBwEAAKCCD9Aw ggSOMIIDdqADAgECAhAOmiw0ECVD4cWj5DqVrT9PMA0GCSqGSIb3DQEBCwUAMGUxCzAJBgNVBAYT AlVTMRUwEwYDVQQKEwxEaWdpQ2VydCBJbmMxGTAXBgNVBAsTEHd3dy5kaWdpY2VydC5jb20xJDAi BgNVBAMTG0RpZ2lDZXJ0IEFzc3VyZWQgSUQgUm9vdCBDQTAeFw0yNDAxMzAwMDAwMDBaFw0zMTEx MDkyMzU5NTlaMEExCzAJBgNVBAYTAkFVMRAwDgYDVQQKEwdWZXJva2V5MSAwHgYDVQQDExdWZXJv a2V5IFNlY3VyZSBFbWFpbCBHMjCCASIwDQYJKoZIhvcNAQEBBQADggEPADCCAQoCggEBAMjvgLKj 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