From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([209.51.188.92]:52849) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1gjmWh-0004oE-8q for qemu-devel@nongnu.org; Wed, 16 Jan 2019 09:50:44 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1gjmWg-0005l5-5x for qemu-devel@nongnu.org; Wed, 16 Jan 2019 09:50:43 -0500 Received: from mx0a-001b2d01.pphosted.com ([148.163.156.1]:42788) by eggs.gnu.org with esmtps (TLS1.0:RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1gjmWf-0005UU-Qi for qemu-devel@nongnu.org; Wed, 16 Jan 2019 09:50:42 -0500 Received: from pps.filterd (m0098394.ppops.net [127.0.0.1]) by mx0a-001b2d01.pphosted.com (8.16.0.22/8.16.0.22) with SMTP id x0GEnGwt101716 for ; Wed, 16 Jan 2019 09:50:23 -0500 Received: from e06smtp01.uk.ibm.com (e06smtp01.uk.ibm.com [195.75.94.97]) by mx0a-001b2d01.pphosted.com with ESMTP id 2q26gbrrd2-1 (version=TLSv1.2 cipher=AES256-GCM-SHA384 bits=256 verify=NOT) for ; Wed, 16 Jan 2019 09:50:22 -0500 Received: from localhost by e06smtp01.uk.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Wed, 16 Jan 2019 14:50:18 -0000 Date: Wed, 16 Jan 2019 15:50:11 +0100 From: Halil Pasic In-Reply-To: <1188d21d-3603-c291-e69b-38d341ae90f4@linux.ibm.com> References: <1547125207-16907-1-git-send-email-pmorel@linux.ibm.com> <1547125207-16907-2-git-send-email-pmorel@linux.ibm.com> <20190116134011.1189b027@oc2783563651> <1188d21d-3603-c291-e69b-38d341ae90f4@linux.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Message-Id: <20190116155011.478db4da@oc2783563651> Subject: Re: [Qemu-devel] [PATCH v2] s390x/pci: Set the iommu region size mpcifc request List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Pierre Morel Cc: Collin Walling , thuth@redhat.com, david@redhat.com, cohuck@redhat.com, qemu-devel@nongnu.org, borntraeger@de.ibm.com, qemu-s390x@nongnu.org, rth@twiddle.net On Wed, 16 Jan 2019 15:16:44 +0100 Pierre Morel wrote: > On 16/01/2019 13:40, Halil Pasic wrote: > > On Tue, 15 Jan 2019 10:35:42 -0500 > > Collin Walling wrote: > > > >> On 1/10/19 8:00 AM, Pierre Morel wrote: > >>> The size of the accessible iommu memory region in the guest > >>> is given to the IOMMU by the guest through the mpcifc request > >>> specifying the PCI Base Address and the PCI Address Limit. > >>> > >>> Let set the size of the IOMMU region to: > >>> (PCI Address Limit) - (PCI Base Address) + 1. > >>> > >>> Signed-off-by: Pierre Morel > >>> --- > >>> hw/s390x/s390-pci-bus.c | 2 +- > >>> 1 file changed, 1 insertion(+), 1 deletion(-) > >>> > >>> diff --git a/hw/s390x/s390-pci-bus.c b/hw/s390x/s390-pci-bus.c > >>> index 69e0671..e97696a 100644 > >>> --- a/hw/s390x/s390-pci-bus.c > >>> +++ b/hw/s390x/s390-pci-bus.c > >>> @@ -660,7 +660,7 @@ void s390_pci_iommu_enable(S390PCIIOMMU *iommu) > >>> char *name = g_strdup_printf("iommu-s390-%04x", iommu->pbdev->uid); > >>> memory_region_init_iommu(&iommu->iommu_mr, sizeof(iommu->iommu_mr), > >>> TYPE_S390_IOMMU_MEMORY_REGION, OBJECT(&iommu->mr), > >>> - name, iommu->pal + 1); > >>> + name, iommu->pal - iommu->pba + 1); > > > > From the the look of this, I would say we basically used the address > > denoting the end of the region as the size of the region. This smells > > like a bug to me, but the commit message and the title ain't clear about > > this, and there is no fixes tag. Because of the latter I did some digging > > and came to commit f7c40aa "s390x/pci: fix failures of dma > > map/unmap" (Yi Min Zhao, 2016-06-19) which basically did the inverse of > > this commit! > > > > My initial motivation was to check if this is stable material. But now > > I'm very confused. I'm admittedly zPCI incompetent. Could some of the > > people that understand what is going on help me feel better about this > > patch? > > > > Regards, > > Halil > > > The patch you speak about corrected the problem described in its comment > by setting the offset address of the subregion to 0, making sure > VFIO_PCI works for Z but introduced a bug we did not see at that time by > making the subregion too large. > > This patch correct the bug, I can add a reference to this with: > fixing: commit f7c40aa1e7feb50bc4d4bc171fa811bdd9a93e51 > @Connie, will you add the Fixes tag? Do we need a cc stable (since broken since 2016-06-19)? @Pierre: So you say it's a bug. What can go wrong because of this? For example if we interpret pal as a size, I guess we could end up with the memory region not fitting the guest memory, or? I'm still pretty much in the dark about the implications of this bug. Regards, Halil