Mark Kettenis <mark.kettenis@xs4all.nl> writes:

>> Date: Fri, 21 Mar 2025 14:24:08 +0100 (CET)
>> From: Stefan Fritsch <sf@openbsd.org>
>
> 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);
>>
>>
>>