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=-8.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED,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 BEF0DC35247 for ; Wed, 5 Feb 2020 18:35:30 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 9813320674 for ; Wed, 5 Feb 2020 18:35:30 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727361AbgBESf3 (ORCPT ); Wed, 5 Feb 2020 13:35:29 -0500 Received: from foss.arm.com ([217.140.110.172]:50994 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727309AbgBESf3 (ORCPT ); Wed, 5 Feb 2020 13:35:29 -0500 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id EACBD1FB; Wed, 5 Feb 2020 10:35:28 -0800 (PST) Received: from donnerap.cambridge.arm.com (usa-sjc-imap-foss1.foss.arm.com [10.121.207.14]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 0F5913F52E; Wed, 5 Feb 2020 10:35:27 -0800 (PST) Date: Wed, 5 Feb 2020 18:35:25 +0000 From: Andre Przywara To: Alexandru Elisei Cc: kvm@vger.kernel.org, will@kernel.org, julien.thierry.kdev@gmail.com, sami.mujawar@arm.com, lorenzo.pieralisi@arm.com, maz@kernel.org Subject: Re: [PATCH v2 kvmtool 24/30] vfio/pci: Don't write configuration value twice Message-ID: <20200205183525.0ed83c94@donnerap.cambridge.arm.com> In-Reply-To: <20200123134805.1993-25-alexandru.elisei@arm.com> References: <20200123134805.1993-1-alexandru.elisei@arm.com> <20200123134805.1993-25-alexandru.elisei@arm.com> Organization: ARM X-Mailer: Claws Mail 3.17.3 (GTK+ 2.24.32; aarch64-unknown-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: kvm-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org On Thu, 23 Jan 2020 13:47:59 +0000 Alexandru Elisei wrote: Hi, > After writing to the device fd as part of the PCI configuration space > emulation, we read back from the device to make sure that the write > finished. The value is read back into the PCI configuration space and > afterwards, the same value is copied by the PCI emulation code. Let's > read from the device fd into a temporary variable, to prevent this > double write. > > The double write is harmless in itself. But when we implement > reassignable BARs, we need to keep track of the old BAR value, and the > VFIO code is overwritting it. > > Signed-off-by: Alexandru Elisei > --- > vfio/pci.c | 4 ++-- > 1 file changed, 2 insertions(+), 2 deletions(-) > > diff --git a/vfio/pci.c b/vfio/pci.c > index abde16dc8693..8a775a4a4a54 100644 > --- a/vfio/pci.c > +++ b/vfio/pci.c > @@ -470,7 +470,7 @@ static void vfio_pci_cfg_write(struct kvm *kvm, struct pci_device_header *pci_hd > struct vfio_region_info *info; > struct vfio_pci_device *pdev; > struct vfio_device *vdev; > - void *base = pci_hdr; > + u32 tmp; Can we make this a u64, please? I am not sure if 64-bit MMIO is allowed for PCI config space accesses, but a guest could do it anyway, and it looks like it would overwrite the vdev pointer on the stack here in this case. Cheers, Andre. > > if (offset == PCI_ROM_ADDRESS) > return; > @@ -490,7 +490,7 @@ static void vfio_pci_cfg_write(struct kvm *kvm, struct pci_device_header *pci_hd > if (pdev->irq_modes & VFIO_PCI_IRQ_MODE_MSI) > vfio_pci_msi_cap_write(kvm, vdev, offset, data, sz); > > - if (pread(vdev->fd, base + offset, sz, info->offset + offset) != sz) > + if (pread(vdev->fd, &tmp, sz, info->offset + offset) != sz) > vfio_dev_warn(vdev, "Failed to read %d bytes from Configuration Space at 0x%x", > sz, offset); > }