From nobody Tue Sep 16 21:34:09 2025 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 vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 25D60C3DA7A for ; Thu, 29 Dec 2022 21:00:38 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233939AbiL2VAg (ORCPT ); Thu, 29 Dec 2022 16:00:36 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:33352 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230458AbiL2VAe (ORCPT ); Thu, 29 Dec 2022 16:00:34 -0500 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id BB647140A0 for ; Thu, 29 Dec 2022 12:59:49 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1672347588; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding; bh=oveyZKRFVQVj32wP0L+KhIamsge517dBdnS11SNoodQ=; b=K0cfRcBvJK+cVkt2euBXYph8z45rCxL0do3/R2Vt/yS75W28CA3MpfNJ3FYsUAXp8db8On wkPniFcpOfukJjKbYURz7Tot/wTwztp2saxUKCRMnUQfvN8myc7qDTMwS6C16dQDKQgBVP YW+2vyoQiPeeEhsZJlKTBZ2Jrc1BgHk= Received: from mimecast-mx02.redhat.com (mx3-rdu2.redhat.com [66.187.233.73]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-398-pwk1Y4LQN9uz_ud6nSwXLA-1; Thu, 29 Dec 2022 15:59:47 -0500 X-MC-Unique: pwk1Y4LQN9uz_ud6nSwXLA-1 Received: from smtp.corp.redhat.com (int-mx05.intmail.prod.int.rdu2.redhat.com [10.11.54.5]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 0D5583C0CD47; Thu, 29 Dec 2022 20:59:47 +0000 (UTC) Received: from virtlab701.virt.lab.eng.bos.redhat.com (virtlab701.virt.lab.eng.bos.redhat.com [10.19.152.228]) by smtp.corp.redhat.com (Postfix) with ESMTP id EA77D53A3; Thu, 29 Dec 2022 20:59:46 +0000 (UTC) From: Paolo Bonzini To: linux-kernel@vger.kernel.org, kvm@vger.kernel.org Subject: [PATCH] KVM: nSVM: clarify recalc_intercepts() wrt CR8 Date: Thu, 29 Dec 2022 15:59:46 -0500 Message-Id: <20221229205946.1826595-1-pbonzini@redhat.com> MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable X-Scanned-By: MIMEDefang 3.1 on 10.11.54.5 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Type: text/plain; charset="utf-8" The mysterious comment "We only want the cr8 intercept bits of L1" dates back to basically the introduction of nested SVM, back when the handling of "less typical" hypervisors was very haphazard. With the development of kvm-unit-tests for interrupt handling, the same code grew another vmcb_clr_intercept for the interrupt window (VINTR) vmexit, this time with a comment that is at least decent. It turns out however that the same comment applies to the CR8 write intercept, which is also a "recheck if an interrupt should be injected" intercept. The CR8 read intercept instead has not been used by KVM for 14 years (commit 649d68643ebf, "KVM: SVM: sync TPR value to V_TPR field in the VMCB"), so do not bother clearing it and let one comment describe both CR8 write and VINTR handling. Signed-off-by: Paolo Bonzini --- arch/x86/kvm/svm/nested.c | 12 +++++------- 1 file changed, 5 insertions(+), 7 deletions(-) diff --git a/arch/x86/kvm/svm/nested.c b/arch/x86/kvm/svm/nested.c index bc9cd7086fa9..add65dd59756 100644 --- a/arch/x86/kvm/svm/nested.c +++ b/arch/x86/kvm/svm/nested.c @@ -138,15 +138,13 @@ void recalc_intercepts(struct vcpu_svm *svm) c->intercepts[i] =3D h->intercepts[i]; =20 if (g->int_ctl & V_INTR_MASKING_MASK) { - /* We only want the cr8 intercept bits of L1 */ - vmcb_clr_intercept(c, INTERCEPT_CR8_READ); - vmcb_clr_intercept(c, INTERCEPT_CR8_WRITE); - /* - * Once running L2 with HF_VINTR_MASK, EFLAGS.IF does not - * affect any interrupt we may want to inject; therefore, - * interrupt window vmexits are irrelevant to L0. + * Once running L2 with HF_VINTR_MASK, EFLAGS.IF and CR8 + * does not affect any interrupt we may want to inject; + * therefore, writes to CR8 are irrelevant to L0, as are + * interrupt window vmexits. */ + vmcb_clr_intercept(c, INTERCEPT_CR8_WRITE); vmcb_clr_intercept(c, INTERCEPT_VINTR); } =20 --=20 2.31.1