From mboxrd@z Thu Jan 1 00:00:00 1970 From: Alex Williamson Subject: Re: [RFC PATCH kernel] vfio-pci: Fix sparse capability when no parts of MSIX BAR can be mapped Date: Wed, 29 Nov 2017 11:27:02 -0700 Message-ID: <20171129112702.51d0a493@t450s.home> References: <20171123045626.17542-1-aik@ozlabs.ru> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Cc: kvm@vger.kernel.org To: Alexey Kardashevskiy Return-path: Received: from mx1.redhat.com ([209.132.183.28]:41056 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750713AbdK2S1D (ORCPT ); Wed, 29 Nov 2017 13:27:03 -0500 In-Reply-To: <20171123045626.17542-1-aik@ozlabs.ru> Sender: kvm-owner@vger.kernel.org List-ID: On Thu, 23 Nov 2017 15:56:26 +1100 Alexey Kardashevskiy wrote: > It is currently possible to have a sparse capability with 1 areas which > starts at 0 and 0 bytes long. One example is: > > Texas Instruments TUSB73x0 SuperSpeed USB 3.0 xHCI Host Controller > [...] > Region 0: Memory at 3fe280000000 (64-bit, non-prefetchable) [size=64K] > Region 2: Memory at 3fe280010000 (64-bit, non-prefetchable) [size=8K] > [...] > Capabilities: [c0] MSI-X: Enable+ Count=8 Masked- > Vector table: BAR=2 offset=00000000 > PBA: BAR=2 offset=00001000 > > With PAGE_SIZE=64K, MSIX BAR occupies the entire BAR2 and cannot be > mapped. > > This makes it explicit - if sparse->areas is empty, then advertise > nr_areas as 0. > > Signed-off-by: Alexey Kardashevskiy > --- > > QEMU gets it right as vfio_setup_region_sparse_mmaps() checks for size > after QEMU's 24acf72b9a291ce "vfio: Handle zero-length sparse mmap ranges" > but why not make it explicit in the first place? > > > --- > drivers/vfio/pci/vfio_pci.c | 4 ++++ > 1 file changed, 4 insertions(+) > > diff --git a/drivers/vfio/pci/vfio_pci.c b/drivers/vfio/pci/vfio_pci.c > index f041b1a..a201c45 100644 > --- a/drivers/vfio/pci/vfio_pci.c > +++ b/drivers/vfio/pci/vfio_pci.c > @@ -597,6 +597,10 @@ static int msix_sparse_mmap_cap(struct vfio_pci_device *vdev, > i++; > } > > + /* With all alignments, there are no gaps left to mmap */ > + if (i == 0) > + sparse->nr_areas = 0; > + Ok, but why does 0 become a special case? Shouldn't we set sparse->nr_areas = i? Thanks, Alex > ret = vfio_info_add_capability(caps, VFIO_REGION_INFO_CAP_SPARSE_MMAP, > sparse); > kfree(sparse);