On 25.02.22 16:16, Ard Biesheuvel wrote:
On Fri, 25 Feb 2022 at 16:12, Alexander Graf <graf@xxxxxxxxxx> wrote:
On 25.02.22 15:33, Jason A. Donenfeld wrote:
On Fri, Feb 25, 2022 at 03:18:43PM +0100, Alexander Graf wrote:
I recall this part of the old thread. From what I understood, using
"VMGENID" + "QEMUVGID" worked /well enough/, even if that wasn't
technically in-spec. Ard noted that relying on _CID like that is
technically an ACPI spec notification. So we're between one spec and
another, basically, and doing "VMGENID" + "QEMUVGID" requires fewer
changes, as mentioned, appears to work fine in my testing.
However, with that said, I think supporting this via "VM_Gen_Counter"
would be a better eventual thing to do, but will require acks and
changes from the ACPI maintainers. Do you think you could prepare your
patch proposal above as something on-top of my tree [1]? And if you can
convince the ACPI maintainers that that's okay, then I'll happily take
the patch.
Sure, let me send the ACPI patch stand alone. No need to include the
VMGenID change in there.
That's fine. If the ACPI people take it for 5.18, then we can count on
it being there and adjust the vmgenid driver accordingly also for 5.18.
I just booted up a Windows VM, and it looks like Hyper-V uses
"Hyper_V_Gen_Counter_V1", which is also quite long, so we can't really
HID match on that either.
Yes, due to the same problem. I'd really prefer we sort out the ACPI
matching before this goes mainline. Matching on _HID is explicitly
discouraged in the VMGenID spec.
OK, this really sucks. Quoting the ACPI spec:
"""
A _HID object evaluates to either a numeric 32-bit compressed EISA
type ID or a string. If a string, the format must be an alphanumeric
PNP or ACPI ID with no asterisk or other leading characters.
A valid PNP ID must be of the form "AAA####" where A is an uppercase
letter and # is a hex digit.
A valid ACPI ID must be of the form "NNNN####" where N is an uppercase
letter or a digit ('0'-'9') and # is a hex digit. This specification
reserves the string "ACPI" for use only with devices defined herein.
It further reserves all strings representing 4 HEX digits for
exclusive use with PCI-assigned Vendor IDs.
"""
So now we have to implement Microsoft's fork of ACPI to be able to use
this device, even if we expose it from QEMU instead of Hyper-V? I
strongly object to that.
Instead, we can match on _HID exposed by QEMU, and cordially invite
Microsoft to align their spec with the ACPI spec.
Doing that would be a backwards incompatible change for Hyper-V, no? I
understand that you're upset about their spec, but that doesn't mean we
can't find a path forward to make it all compatible.
IMHO just matching on the first 9 bytes of the _CID/_HID string is
perfectly fine. It follows the spec, but still allows for weird
identifiers like this one to work.
I don't understand the rush here. This had been sitting on the ML for 1
year - and now suddenly talking the match through properly and getting
VMGenID spec compatible matching support into the ACPI core is a
problem? What did I miss? :)
Alex
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