From: Mark Kettenis Subject: Re: Use acpipci in VMs To: Stefan Fritsch Cc: dv@sisu.io, tech@openbsd.org Date: Mon, 31 Mar 2025 23:06:21 +0200 > Date: Mon, 31 Mar 2025 17:58:26 +0200 (CEST) > From: Stefan Fritsch > > On Mon, 31 Mar 2025, Dave Voutila wrote: > > > Mark Kettenis writes: > > > > >> Date: Fri, 21 Mar 2025 14:24:08 +0100 (CET) > > >> From: Stefan Fritsch > > > > > > Hi Stefan, > > > > > >> Hi, > > >> > > >> On Sun, 16 Mar 2025, Stefan Fritsch wrote: > > >> > there were some reports that vio on KVM/qemu sometimes panics with > > >> > > > >> > vq_size not power of two: 65535 > > >> > > > >> > but I could never reproduce it. bluhm@ now got me a test setup where the > > >> > bsd kernel is PXE booted on qemu in 440fx mode, and there it is > > >> > reproducible. > > >> > > > >> > After some debugging it seems that seabios or ipxe maps the PCI BARs at > > >> > 0x380000000000-0x380080000000 which is outside the allowed range in > > >> > pci_init_extents(). On the other hand, in 440fx mode, qemu seems to > > >> > produce ACPI 1.x tables and there is a check in acpipci_attach() that for > > >> > ACPI < 5.x, the PCI infos from _CRS are not used. OpenBSD will then > > >> > disable the BARs and when mapping them again in vio_attach(), it will > > >> > sometimes choose adresses that do not work, reads return 0xff and writes > > >> > are ignored. I guess this is becuase the address (in my case 0xbff14000) > > >> > lies outside the PCI window of the emulated chipset. > > >> > > > >> > I have put dmesg, acpi tables and other info at > > >> > https://www.sfritsch.de/~stf/vq-panic/ > > >> > > > >> > Qemu in q35 mode produces ACPI 3.x tables, so it may also be affected. > > >> > > > >> > There may be three ways to fix this: > > >> > > > >> > 1) increase the allowed range for pcimem in pci_init_extents(). This is > > >> > what the diff below does. > > >> > > > >> > 2) somehow make acpipci_attach() use the ACPI infos on qemu. I have > > >> > verified that removing the version check fixes the issue. Since removing > > >> > the version check seems to break many other systems, this would have to be > > >> > a qemu specific quirk. > > >> > > > >> > 3) try to make OpenBSD reliably map the BARs somewhere where it works. Is > > >> > there a way for OpenBSD to get the info where the PCI window is without > > >> > trusting ACPI? > > >> > > > >> > I remember at least one report of this issue on i386. Any idea how to fix > > >> > it there? > > >> > > >> Mark Patruck noticed that these issues seem to be caused by some > > >> relatively recent changes in seabios. > > >> > > >> https://mail.coreboot.org/hyperkitty/list/seabios@seabios.org/message/R7FOQMMYWVX577QNIA2AKUAGOZKNJIAP/ > > >> https://gitlab.com/qemu-project/seabios/-/commit/df9dd418b3b0e586cb208125094620fc7f90f23d > > >> > > >> A workaround seems to be to configure the VM with <= 3GB memory. > > >> > > >> The problem may become more wide-spread with 7.7, since we now default to > > >> virtio 1.x, which uses MMIO on qemu, compared to virtio 0.9 which uses PIO > > >> BARs. Therefore it would be nice to get a fix in before the release, if it > > >> is not too late already. > > >> > > >> The diff below uses acpipci / _CRS also with old ACPI versions if running > > >> on a hypervisor. I think the chance that it will break unrelated systems > > >> is low. It does not change behavior on vmd, where no acpi attaches at all. > > >> > > >> ok? > > > > > > I hate these VM quirks. Why are folks still emulating hardware from > > > the 1990's when running a modern OS? > > > > ...like vmd(8). /gasp /vomit /shudder > > > > At least our ACPI isn't broken (because it doesn't exist). > > > > > > > > Anyway, not much we can do about that I guess. But maybe we can have > > > a bit more consistency? We already have a check to enable MSI for > > > QEMU. And since this really is a QEMU issue, maybe it would be better > > > to use a PCI_SUBSYS_ID_REG check here? > > I am not sure. We have a quirk to detect old systems where ACPI cannot be > trusted. If the HV cpuid bit is set, the system cannot be that old and it > is reasonable not to use the broken-acpi quirk. > > A diff with PCI_SUBSYS_ID_REG is attached below and works, too. I like the > cpuid diff better. But if you want the PCI_SUBSYS_ID_REG diff, let's > commit that so this get's fixed before release. Fair enough. Go with cpuid fix. We can always revisit this later. > > >> diff --git a/sys/arch/amd64/pci/acpipci.c b/sys/arch/amd64/pci/acpipci.c > > >> index 51cd1360383..2e3236772bb 100644 > > >> --- a/sys/arch/amd64/pci/acpipci.c > > >> +++ b/sys/arch/amd64/pci/acpipci.c > > >> @@ -152,7 +152,7 @@ acpipci_attach(struct device *parent, struct device *self, void *aux) > > >> > > >> aml_parse_resource(&res, acpipci_parse_resources, sc); > > >> > > >> - if (sc->sc_acpi->sc_major < 5) { > > >> + if (sc->sc_acpi->sc_major < 5 && (cpu_ecxfeature & CPUIDECX_HV) == 0) { > > >> extent_destroy(sc->sc_ioex); > > >> extent_destroy(sc->sc_memex); > > >> > > >> > > >> > > > > > > diff --git a/sys/arch/amd64/pci/acpipci.c b/sys/arch/amd64/pci/acpipci.c > index 51cd1360383..b546747306a 100644 > --- a/sys/arch/amd64/pci/acpipci.c > +++ b/sys/arch/amd64/pci/acpipci.c > @@ -153,12 +153,25 @@ acpipci_attach(struct device *parent, struct device *self, void *aux) > aml_parse_resource(&res, acpipci_parse_resources, sc); > > if (sc->sc_acpi->sc_major < 5) { > - extent_destroy(sc->sc_ioex); > - extent_destroy(sc->sc_memex); > + pcitag_t tag; > + pcireg_t id; > > - pci_init_extents(); > - sc->sc_ioex = pciio_ex; > - sc->sc_memex = pcimem_ex; > + tag = pci_make_tag(0, sc->sc_bus, 0, 0); > + id = pci_conf_read(0, tag, PCI_SUBSYS_ID_REG); > + > + /* > + * We don't trust ACPI versions < 5, except on qemu, which > + * emulates ancient hardware with ACPI 1 tables. > + */ > + if (PCI_VENDOR(id) != PCI_VENDOR_QUMRANET) > + { > + extent_destroy(sc->sc_ioex); > + extent_destroy(sc->sc_memex); > + > + pci_init_extents(); > + sc->sc_ioex = pciio_ex; > + sc->sc_memex = pcimem_ex; > + } > } > > printf("\n"); > >