From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mx0b-001b2d01.pphosted.com ([148.163.158.5]:35326 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1726102AbgHMNJ5 (ORCPT ); Thu, 13 Aug 2020 09:09:57 -0400 Subject: Re: [PATCH v2] PCI: Introduce flag for detached virtual functions References: <1597260071-2219-1-git-send-email-mjrosato@linux.ibm.com> <1597260071-2219-2-git-send-email-mjrosato@linux.ibm.com> <20200812143254.2f080c38@x1.home> From: Matthew Rosato Message-ID: Date: Thu, 13 Aug 2020 09:09:45 -0400 MIME-Version: 1.0 In-Reply-To: <20200812143254.2f080c38@x1.home> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-s390-owner@vger.kernel.org List-ID: To: Alex Williamson Cc: bhelgaas@google.com, schnelle@linux.ibm.com, pmorel@linux.ibm.com, mpe@ellerman.id.au, oohall@gmail.com, linux-s390@vger.kernel.org, linux-kernel@vger.kernel.org, kvm@vger.kernel.org, linux-pci@vger.kernel.org On 8/12/20 4:32 PM, Alex Williamson wrote: > On Wed, 12 Aug 2020 15:21:11 -0400 > Matthew Rosato wrote: > >> s390x has the notion of providing VFs to the kernel in a manner >> where the associated PF is inaccessible other than via firmware. >> These are not treated as typical VFs and access to them is emulated >> by underlying firmware which can still access the PF. After >> abafbc55 however these detached VFs were no longer able to work >> with vfio-pci as the firmware does not provide emulation of the >> PCI_COMMAND_MEMORY bit. In this case, let's explicitly recognize >> these detached VFs so that vfio-pci can allow memory access to >> them again. >> > > Might as well include a fixes tag too. > > Fixes: abafbc551fdd ("vfio-pci: Invalidate mmaps and block MMIO access on disabled memory") > > You might also extend the sha1 in the log to 12 chars as well, or > replace it with a reference to the fixes tag. > Sure. >> Signed-off-by: Matthew Rosato >> --- ..snip.. >> diff --git a/include/linux/pci.h b/include/linux/pci.h >> index 8355306..23a6972 100644 >> --- a/include/linux/pci.h >> +++ b/include/linux/pci.h >> @@ -445,6 +445,7 @@ struct pci_dev { >> unsigned int is_probed:1; /* Device probing in progress */ >> unsigned int link_active_reporting:1;/* Device capable of reporting link active */ >> unsigned int no_vf_scan:1; /* Don't scan for VFs after IOV enablement */ >> + unsigned int detached_vf:1; /* VF without local PF access */ > > Is there too much implicit knowledge in defining a "detached VF"? For > example, why do we know that we can skip the portion of > vfio_config_init() that copies the vendor and device IDs from the > struct pci_dev into the virtual config space? It's true on s390x, but > I think that's because we know that firmware emulates those registers > for us. We also skip the INTx pin register sanity checking. Do we do > that because we haven't installed the broken device into an s390x > system? Because we know firmware manages that for us too? Or simply > because s390x doesn't support INTx anyway, and therefore it's another > architecture implicit decision? That's a fair point. This was also discussed (overnight for me) in another thread that this patch is very s390-specific. It doesn't have to be, we could also emulate these additional pieces to make things more general-purpose here. > > If detached_vf is really equivalent to is_virtfn for all cases that > don't care about referencing physfn on the pci_dev, then we should > probably have a macro to that effect. Otherwise, if we're just trying > to describe that the memory bit of the command register is > unimplemented but always enabled, like a VF, should we specifically > describe that attribute instead? If so, should we instead do that with > pci_dev_flags_t? Thanks, Well, that's the particular issue that got us looking at this but I'm not so sure we wouldn't find further oddities later, hence the desire for a more general-purpose bit. > > Alex > >> pci_dev_flags_t dev_flags; >> atomic_t enable_cnt; /* pci_enable_device has been called */ >> >