ignore bit 0 in pci CONFIG_ADDRESS register write for Type 1 access

Bug #1901359 reported by cinap_lenrek
This bug affects 1 person
Affects Status Importance Assigned to Milestone

Bug Description

I'v recently stumbled upon a bug in the Plan9 PCI config space access routines for config mode #1.

The code used to set bit 0 in the CONFIG_ADDRESS register for a Type 1 access.

This was most likely a misreading of the PCI local bus specification on our side.

However, in the PCI local bus specification 3.0, it states the following:

> Software Generation of Configuration Transactions
> ...
> For Type 1 translations, the host bridge directly copies the contents of the
> CONFIG_ADDRESS register (excluding bits 31 and 0) onto the PCI AD lines during the
> address phase of a configuration transaction making sure that AD[1::0] is "01".

note the: "excluding bits 31 and 0"

What happens in qemu instead is that it uses bit 0 of the CONFIG_ADDRESS
register as part of the register offset (when it probably should ignore it)
when translating from Type 1 to Type 0 address. So once it reaches the device
behind the bridge the register address is off by one.

Revision history for this message
cinap_lenrek (cinaplenrek) wrote :

is anybody home?

Revision history for this message
Thomas Huth (th-huth) wrote :

Yeah, the bug tracker here on Launchpad is somewhat neglected ... Therefore:
The QEMU project is currently moving its bug tracking to another system.
For this we need to know which bugs are still valid and which could be
closed already. Thus we are setting the bug state to "Incomplete" now.

If the bug has already been fixed in the latest upstream version of QEMU,
then please close this ticket as "Fix released".

If it is not fixed yet and you think that this bug report here is still
valid, then you have two options:

1) If you already have an account on gitlab.com, please open a new ticket
for this problem in our new tracker here:


and then close this ticket here on Launchpad (or let it expire auto-
matically after 60 days). Please mention the URL of this bug ticket on
Launchpad in the new ticket on GitLab.

2) If you don't have an account on gitlab.com and don't intend to get
one, but still would like to keep this ticket opened, then please switch
the state back to "New" or "Confirmed" within the next 60 days (other-
wise it will get closed as "Expired"). We will then eventually migrate
the ticket automatically to the new system (but you won't be the reporter
of the bug in the new system and thus you won't get notified on changes

Thank you and sorry for the inconvenience.

Changed in qemu:
status: New → Incomplete
Revision history for this message
Launchpad Janitor (janitor) wrote :

[Expired for QEMU because there has been no activity for 60 days.]

Changed in qemu:
status: Incomplete → Expired
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