linux-kernel - Re: Bug report: the extended PCI config space is missed with 6.2-rc2

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Message-ID: <20230105203757.GA1166631@bhelgaas>
Date:   Thu, 5 Jan 2023 14:37:57 -0600
From:   Bjorn Helgaas <helgaas@...nel.org>
To:     "Luck, Tony" <tony.luck@...el.com>
Cc:     "Williams, Dan J" <dan.j.williams@...el.com>,
        "Liang, Kan" <kan.liang@...ux.intel.com>,
        "bhelgaas@...gle.com" <bhelgaas@...gle.com>,
        "hdegoede@...hat.com" <hdegoede@...hat.com>,
        "kernelorg@...ead.fr" <kernelorg@...ead.fr>,
        "kjhambrick@...il.com" <kjhambrick@...il.com>,
        "2lprbe78@...k.com" <2lprbe78@...k.com>,
        "nicholas.johnson-opensource@...look.com.au" 
        <nicholas.johnson-opensource@...look.com.au>,
        "benoitg@...us.ca" <benoitg@...us.ca>,
        "mika.westerberg@...ux.intel.com" <mika.westerberg@...ux.intel.com>,
        "wse@...edocomputers.com" <wse@...edocomputers.com>,
        "mumblingdrunkard@...tonmail.com" <mumblingdrunkard@...tonmail.com>,
        "linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "Box, David E" <david.e.box@...el.com>,
        "Sun, Yunying" <yunying.sun@...el.com>
Subject: Re: Bug report: the extended PCI config space is missed with 6.2-rc2

On Thu, Jan 05, 2023 at 07:58:47PM +0000, Luck, Tony wrote:
> > Definitely an ambiguity / conflict, but not sure it is a bug when you
> > look at from the perspective of how would an EFI runtime service use
> > ECAM/MMCONFIG space? 
> >
> > Would it be enough to add this clarification in "EFI 2.9 Table 7-6
> > Memory Type Usage after ExitBootServices()"?
> >
> > s/This memory is not used by the OS./This memory is not used by the OS,
> > unless ACPI declares it for another purpose./
> 
> In the case of the EDAC driver there isn't any ACPI declaration.  It just does
> pci_get_device() to find the devices it needs to use with a lookup based on
> vendor-id and device-id.

The EDAC driver wouldn't have any ACPI stuff in it; it's just that
Linux is looking for ACPI info about the ECAM area.

I think the problem here is that the ECAM/MMCONFIG code checks to make
sure the ECAM space is reserved somewhere.  If it doesn't find a
reservation either in E820 [1] or by PNP0C01/PNP0C02 _CRS methods [2],
it decides it's not safe to use ECAM, which means we may only have the
old accessors that can only reach 256 bytes of config space.

Bjorn

[1] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/arch/x86/pci/mmconfig-shared.c?id=v6.1#n447
[2] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/arch/x86/pci/mmconfig-shared.c?id=v6.1#n428