From: Dave Voutila Subject: Re: Use acpipci in VMs To: Mark Kettenis Cc: Stefan Fritsch , tech@openbsd.org Date: Mon, 31 Mar 2025 11:35:16 -0400 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? > >> 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); >> >> >>