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=-8.3 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_2 autolearn=ham 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 BC58DC388F7 for ; Thu, 12 Nov 2020 13:03:46 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 30A4122201 for ; Thu, 12 Nov 2020 13:03:46 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="OznJhtF0" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728254AbgKLNDp (ORCPT ); Thu, 12 Nov 2020 08:03:45 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:45826 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728134AbgKLNDo (ORCPT ); Thu, 12 Nov 2020 08:03:44 -0500 Received: from merlin.infradead.org (merlin.infradead.org [IPv6:2001:8b0:10b:1231::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 92E5EC0613D1 for ; Thu, 12 Nov 2020 05:03:44 -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:Date:Cc:To: From:Subject:Message-ID:Sender:Reply-To:Content-Transfer-Encoding:Content-ID: Content-Description:In-Reply-To:References; bh=Ain4p74aeMuMv/rK1nTwcANb7HDsGwcGYCFm+acwIPs=; b=OznJhtF0JIUSvFlS3eDVIkPmPf APRItYNW4qkDjfWQeEI2wdUY1OHHYkG016G1rOWFGnZKwMw6BJxHAsiA24eNREtp0yXh7C5SAcYN/ kK4mGvn99tQ9nlgg1kQNw8ZsNsGcymYdmfuEczixD2LitVMKb3zd4zcrtcODXWgvwLLwXATofd1CH wov2ZJIkqiQXSxUB5M7KrjGyow1R7CjC8ygkx7pmob13U6hhYocRgauxtUHgl7WIUJSsci7QEWUAL BjA/9F72fJjEOPltwZbKVP812jFeaOBt6anZpNzxR/fbAcOqoc1Q6c2mF6ELOE8Td/qPS64EQ5GEh HGl87orA==; Received: from 54-240-197-238.amazon.com ([54.240.197.238] helo=u3832b3a9db3152.ant.amazon.com) by merlin.infradead.org with esmtpsa (Exim 4.92.3 #3 (Red Hat Linux)) id 1kdCGK-0006gt-0a; Thu, 12 Nov 2020 13:03:40 +0000 Message-ID: <62918f65ec78f8990278a6a0db0567968fa23e49.camel@infradead.org> Subject: [RFC] Further hack request_interrupt_window handling to work around kvm_cpu_has_interrupt() nesting breakage From: David Woodhouse To: kvm Cc: "Sironi, Filippo" , "Raslan, KarimAllah" Date: Thu, 12 Nov 2020 13:03:38 +0000 Content-Type: multipart/signed; micalg="sha-256"; protocol="application/x-pkcs7-signature"; boundary="=-5KtFOFqM+knAaWOipgHq" 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 --=-5KtFOFqM+knAaWOipgHq Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable In kvm_cpu_has_interrupt() we see the following FIXME: /* * FIXME: interrupt.injected represents an interrupt that it's * side-effects have already been applied (e.g. bit from IRR * already moved to ISR). Therefore, it is incorrect to rely * on interrupt.injected to know if there is a pending * interrupt in the user-mode LAPIC. * This leads to nVMX/nSVM not be able to distinguish * if it should exit from L2 to L1 on EXTERNAL_INTERRUPT on * pending interrupt or should re-inject an injected * interrupt. */ I'm using nested VMX for testing, while I add split-irqchip support to my VMM. I see the vCPU lock up when attempting to deliver an interrupt. What seems to happen is that request_interrupt_window is set, causing an immediate vmexit because an IRQ *can* be delivered. But then kvm_vcpu_ready_for_interrupt_injection() returns false, because kvm_cpu_has_interrupt() is true. Because that returns false, the kernel just continues looping in vcpu_run(), constantly vmexiting and going right back in. This utterly na=C3=AFve hack makes my L2 guest boot properly, by not enabling the irq window when we were going to ignore the exit anyway. Is there a better fix? I must also confess I'm working on a slightly older kernel in L1, and have forward-ported to a more recent tree without actually testing because from inspection it looks like exactly the same issue still exists. diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index 397f599b20e5..e23f0c8b4a16 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -8830,7 +8830,10 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu) } =20 inject_pending_event(vcpu, &req_immediate_exit); - if (req_int_win) + /* Don't enable the interrupt window for userspace if + * kvm_cpu_has_interrupt() is set and we'd never actually + * exit with ready_for_interrupt_window set anyway. */ + if (req_int_win && !kvm_cpu_has_interrupt(vcpu) kvm_x86_ops.enable_irq_window(vcpu); =20 if (kvm_lapic_enabled(vcpu)) { --=-5KtFOFqM+knAaWOipgHq Content-Type: application/x-pkcs7-signature; name="smime.p7s" Content-Disposition: attachment; filename="smime.p7s" Content-Transfer-Encoding: base64 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