From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Subject: Re: [PATCH 0/4] vfio-pci/zdev: Fixing s390 vfio-pci ISM support References: <1611086550-32765-1-git-send-email-mjrosato@linux.ibm.com> From: Pierre Morel Message-ID: Date: Wed, 20 Jan 2021 10:02:08 +0100 MIME-Version: 1.0 In-Reply-To: <1611086550-32765-1-git-send-email-mjrosato@linux.ibm.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit List-ID: To: Matthew Rosato , alex.williamson@redhat.com, cohuck@redhat.com, schnelle@linux.ibm.com Cc: borntraeger@de.ibm.com, hca@linux.ibm.com, gor@linux.ibm.com, gerald.schaefer@linux.ibm.com, linux-s390@vger.kernel.org, kvm@vger.kernel.org, linux-kernel@vger.kernel.org On 1/19/21 9:02 PM, Matthew Rosato wrote: > Today, ISM devices are completely disallowed for vfio-pci passthrough as > QEMU will reject the device due to an (inappropriate) MSI-X check. > However, in an effort to enable ISM device passthrough, I realized that the > manner in which ISM performs block write operations is highly incompatible > with the way that QEMU s390 PCI instruction interception and > vfio_pci_bar_rw break up I/O operations into 8B and 4B operations -- ISM > devices have particular requirements in regards to the alignment, size and > order of writes performed. Furthermore, they require that legacy/non-MIO > s390 PCI instructions are used, which is also not guaranteed when the I/O > is passed through the typical userspace channels. > > As a result, this patchset proposes a new VFIO region to allow a guest to > pass certain PCI instruction intercepts directly to the s390 host kernel > PCI layer for execution, pinning the guest buffer in memory briefly in > order to execute the requested PCI instruction. > > Changes from RFC -> v1: > - No functional changes, just minor commentary changes -- Re-posting along > with updated QEMU set. > Hi, there are is a concerns about this patch series: As the title says it is strongly related to ISM hardware. Why being so specific? Regards, Pierre -- Pierre Morel IBM Lab Boeblingen