Re: [PATCH v6] x86/PCI: Ignore E820 reservations for bridge windows on newer systems

[Bjorn Helgaas <helgaas@kernel.org>]

On Mon, Jan 10, 2022 at 12:41:37PM +0100, Hans de Goede wrote:
> Hi All,
> 
> On 12/17/21 15:13, Hans de Goede wrote:
> > Some BIOS-es contain a bug where they add addresses which map to system
> > RAM in the PCI host bridge window returned by the ACPI _CRS method, see
> > commit 4dc2287c1805 ("x86: avoid E820 regions when allocating address
> > space").
> > 
> > To work around this bug Linux excludes E820 reserved addresses when
> > allocating addresses from the PCI host bridge window since 2010.
> > 
> > Recently (2019) some systems have shown-up with E820 reservations which
> > cover the entire _CRS returned PCI bridge memory window, causing all
> > attempts to assign memory to PCI BARs which have not been setup by the
> > BIOS to fail. For example here are the relevant dmesg bits from a
> > Lenovo IdeaPad 3 15IIL 81WE:
> > 
> >  [mem 0x000000004bc50000-0x00000000cfffffff] reserved
> >  pci_bus 0000:00: root bus resource [mem 0x65400000-0xbfffffff window]
> > 
> > The ACPI specifications appear to allow this new behavior:
> > 
> > The relationship between E820 and ACPI _CRS is not really very clear.
> > ACPI v6.3, sec 15, table 15-374, says AddressRangeReserved means:
> > 
> >   This range of addresses is in use or reserved by the system and is
> >   not to be included in the allocatable memory pool of the operating
> >   system's memory manager.
> > 
> > and it may be used when:
> > 
> >   The address range is in use by a memory-mapped system device.
> > 
> > Furthermore, sec 15.2 says:
> > 
> >   Address ranges defined for baseboard memory-mapped I/O devices, such
> >   as APICs, are returned as reserved.
> > 
> > A PCI host bridge qualifies as a baseboard memory-mapped I/O device,
> > and its apertures are in use and certainly should not be included in
> > the general allocatable pool, so the fact that some BIOS-es reports
> > the PCI aperture as "reserved" in E820 doesn't seem like a BIOS bug.
> > 
> > So it seems that the excluding of E820 reserved addresses is a mistake.
> > 
> > Ideally Linux would fully stop excluding E820 reserved addresses,
> > but then the old systems this was added for will regress.
> > Instead keep the old behavior for old systems, while ignoring
> > the E820 reservations for any systems from now on.
> > 
> > Old systems are defined here as BIOS year < 2018, this was chosen to make
> > sure that E820 reservations will not be used on the currently affected
> > systems, while at the same time also taking into account that the systems
> > for which the E820 checking was originally added may have received BIOS
> > updates for quite a while (esp. CVE related ones), giving them a more
> > recent BIOS year then 2010.
> > 
> > BugLink: https://bugzilla.kernel.org/show_bug.cgi?id=206459
> > BugLink: https://bugzilla.redhat.com/show_bug.cgi?id=1868899
> > BugLink: https://bugzilla.redhat.com/show_bug.cgi?id=1871793
> > BugLink: https://bugs.launchpad.net/bugs/1878279
> > BugLink: https://bugs.launchpad.net/bugs/1931715
> > BugLink: https://bugs.launchpad.net/bugs/1932069
> > BugLink: https://bugs.launchpad.net/bugs/1921649
> > Cc: Benoit Grégoire <benoitg@coeus.ca>
> > Cc: Hui Wang <hui.wang@canonical.com>
> > Cc: stable@vger.kernel.org
> > Reviewed-by: Mika Westerberg <mika.westerberg@linux.intel.com>
> > Acked-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
> > Acked-by: Bjorn Helgaas <bhelgaas@google.com>
> > Signed-off-by: Hans de Goede <hdegoede@redhat.com>
> > ---
> > Changes in v6:
> > - Remove the possibility to change the behavior from the commandline
> >   because of worries that users may use this to paper over other problems
> 
> ping ?

Thanks, Hans.  Maybe I'm quixotic, but I'm still hoping for an
approach based on firmware behavior instead of firmware date.  If
nobody else tries, I will eventually try myself, but I don't have any
ETA.

Bjorn