Re: [PATCH v2] x86/PCI: Ignore E820 reservations for bridge windows on newer systems

[Hui Wang]

On 10/11/21 9:53 PM, Mika Westerberg wrote:
> Hi Hans,
>
> On Mon, Oct 11, 2021 at 11:05:31AM +0200, Hans de Goede wrote:
> > Some BIOS-es contain a bug where they add addresses which map to system RAM
> > in the PCI bridge memory window returned by the ACPI _CRS method, see
> > commit 4dc2287c1805 ("x86: avoid E820 regions when allocating address
> > space").
> >
> > To avoid this Linux by default excludes E820 reservations when allocating
> > addresses since 2010. Windows however ignores E820 reserved regions for PCI
> > mem allocations, so in hindsight Linux honoring them is a problem.
> >
> > Recently (2020) 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:
> >
> > [    0.000000] BIOS-e820: [mem 0x000000004bc50000-0x00000000cfffffff] reserved
> > [    0.557473] pci_bus 0000:00: root bus resource [mem 0x65400000-0xbfffffff window]
> >
> > Ideally Linux would fully stop honoring E820 reservations for PCI mem
> > allocations, but then the old systems this was added for will regress.
> > Instead keep the old behavior for old systems, while ignoring the E820
> > reservations like Windows does for any systems from now on.
> >
> > Old systems are defined here as BIOS year < 2018, this was chosen to
> > make sure that pci_use_e820 will not be set on the currently affected
> > systems, while at the same time also taking into account that the
> > systems for which the E820 checking was orignally added may have
> > received BIOS updates for quite a while (esp. CVE related ones),
> > giving them a more recent BIOS year then 2010.
> >
> > Also add pci=no_e820 and pci=use_e820 options to allow overriding
> > the BIOS year heuristic.
> >
> > 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@xxxxxxxx>
> > Cc: Hui Wang <hui.wang@xxxxxxxxxxxxx>
> > Signed-off-by: Hans de Goede <hdegoede@xxxxxxxxxx>
> Thanks for fixing this! Few comments below. Otherwise looks good,
>
> Reviewed-by: Mika Westerberg <mika.westerberg@xxxxxxxxxxxxxxx>
Thanks for fixing this! We almost reach a solution. :-)

Thanks,

Hui.