linux-kernel - Re: acpi PNP0A03:00: fail to add MMCONFIG information, can't access extended PCI configuration space under this bridge.

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Date:   Fri, 29 Jul 2022 17:22:38 -0500
From:   Bjorn Helgaas <helgaas@...nel.org>
To:     Paul Menzel <pmenzel@...gen.mpg.de>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        x86@...nel.org, Bjorn Helgaas <bhelgaas@...gle.com>,
        linux-pci@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>,
        it+x86@...gen.mpg.de, Robert Dinse <nanook@...imo.com>
Subject: Re: acpi PNP0A03:00: fail to add MMCONFIG information, can't access
 extended PCI configuration space under this bridge.

[+cc Robert]

On Mon, Feb 15, 2021 at 05:53:51PM +0100, Paul Menzel wrote:
> Dear Linux folks,
> 
> 
> All the way up to QEMU emulator version 5.2.0 (Debian 1:5.2+dfsg-5) and
> Linux 5.10.13, Linux logs the warning below:
> 
>     acpi PNP0A03:00: fail to add MMCONFIG information, can't access extended
> PCI configuration space under this bridge.
> 
> One way to reproduce it:
> 
>     qemu-system-x86_64 -enable-kvm -m 2G -hda /dev/shm/debian.img -kernel
> /boot/vmlinuz-5.10.0-3-amd64 -initrd /boot/initrd.img-5.10.0-3-amd64 -append
> root="/dev/sda1 console=ttyS0,115200" -serial stdio
> 
> Please find more details and the full log in the Bugzilla issue #211765 [1].
> 
> 
> Kind regards,
> 
> Paul
> 
> 
> [1]: https://bugzilla.kernel.org/show_bug.cgi?id=211765
>      "[Bug 211765] acpi PNP0A03:00: fail to add MMCONFIG information, can't
> access extended PCI configuration space under this bridge."

Do you know whether qemu implements extended config space?  Extended
config space is offsets 0x100-0xfff.  I think Linux only supports
extended capabilities in that area (AER, VC, ACS, SR-IOV, etc).  Most
of these are probably not of interest in a virtualized environment, so
I wouldn't be surprised if qemu doesn't support them.

Bjorn