On Mon, 27 Jul 2020 17:40:39 +0200 Pierre Morel <pmo...@linux.ibm.com> wrote:
> On 2020-07-23 18:29, Alex Williamson wrote: > > On Thu, 23 Jul 2020 11:13:55 -0400 > > Matthew Rosato <mjros...@linux.ibm.com> wrote: > > > >> I noticed that after kernel commit abafbc55 'vfio-pci: Invalidate mmaps > >> and block MMIO access on disabled memory' vfio-pci via qemu on s390x > >> fails spectacularly, with errors in qemu like: > >> > >> qemu-system-s390x: vfio_region_read(0001:00:00.0:region0+0x0, 4) failed: > >> Input/output error > >> > >> From read to bar 0 originating out of > >> hw/s390x/s390-pci-inst.c:zpci_read_bar(). > >> > >> So, I'm trying to figure out how to get vfio-pci happy again on s390x. > >> From > >> a bit of tracing, we seem to be triggering the new trap in > >> __vfio_pci_memory_enabled(). Sure enough, if I just force this function to > >> return 'true' as a test case, things work again. > >> The included patch attempts to enforce the setting, which restores > >> everything > >> to working order but also triggers vfio_bar_restore() in the process.... > >> So > >> this isn't the right answer, more of a proof-of-concept. > >> > >> @Alex: Any guidance on what needs to happen to make qemu-s390x happy with > >> this > >> recent kernel change? > > > > Bummer! I won't claim to understand s390 PCI, but if we have a VF > > exposed to the "host" (ie. the first level where vfio-pci is being > > used), but we can't tell that it's a VF, how do we know whether the > > memory bit in the command register is unimplemented because it's a VF > > or unimplemented because the device doesn't support MMIO? How are the > > device ID, vendor ID, and BAR registers virtualized to the host? Could > > the memory enable bit also be emulated by that virtualization, much > > like vfio-pci does for userspace? If the other registers are > > virtualized, but these command register bits are left unimplemented, do > > we need code to deduce that we have a VF based on the existence of MMIO > > BARs, but lack of memory enable bit? Thanks, > > > > Alex > > Alex, Matt, > > in s390 we have the possibility to assign a virtual function to a > logical partition as function 0. > In this case it can not be treated as a virtual function but must be > treated as a physical function. > This is currently working very well. > However, these functions do not set PCI_COMMAND_MEMORY as we need. Where is the vendor and device ID virtualization done for these devices, we can't have a PF with IDs 0000:0000. > Shouldn't we fix this inside the kernel, to keep older QMEU working? > > Then would it be OK to add a new bit/boolean inside the > pci_dev/vfio_pci_device like, is_detached_vfn, that we could set during > enumeration and test inside __vfio_pci_memory_enabled() to return true? Probably each instance of is_virtfn in vfio-pci should be looked at to see if it applies to s390. If we're going to recognize this as a VF, I'd rather we complete the emulation that the lower level hypervisor has missed. If we can enable all the is_virtfn code on s390, then we should probably cache is_virtfn on the vfio_pci_device object and allow s390 a place to set it once at probe or enable time. > In the enumeration we have the possibility to know if the function is a > HW/Firmware virtual function on devfn 0 or if it is created by SRIOV. > > It seems an easy fix without side effects. > > What do you think? It sure seems preferable to recognize that it is a VF in the kernel than to require userspace to have arch specific hacks. Thanks, Alex