Re: [PATCH] x86/PCI: Add pci=no_e820 cmdline option to ignore E820 reservations for bridge windows

[Randy Dunlap]

On 10/5/21 8:09 AM, 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, instead it avoids these BIOS bugs by allocates addresses
> top-down.
>
> 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]
>
> Add a pci=no_e820 option which allows disabling the E820 reservations
> check, while still honoring the _CRS provided resources.
>
> And automatically enable this on the "Lenovo IdeaPad 3 15IIL05" to fix
> the touchpad not working on this laptop.
>
> Also add a pci=use_e820 option to allow overruling the results of
> DMI quirks defaulting to no_e820 on some systems.
>
> 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/ubuntu/+source/linux-signed-hwe/+bug/1878279
> Signed-off-by: Hans de Goede <hdegoede@xxxxxxxxxx>

Hi Hans,

Please update Documentation/admin-guide/kernel-parameters.txt also.

> ---
>   arch/x86/include/asm/pci_x86.h | 10 ++++++++++
>   arch/x86/kernel/resource.c     | 17 +++++++++++++++++
>   arch/x86/pci/acpi.c            | 26 ++++++++++++++++++++++++++
>   arch/x86/pci/common.c          |  6 ++++++
>   4 files changed, 59 insertions(+)

> diff --git a/arch/x86/kernel/resource.c b/arch/x86/kernel/resource.c
> index 9b9fb7882c20..6069d86021f0 100644
> --- a/arch/x86/kernel/resource.c
> +++ b/arch/x86/kernel/resource.c

> @@ -23,11 +24,27 @@ static void resource_clip(struct resource *res, resource_size_t start,
>   		res->start = end + 1;
>   }
>   
> +/*
> + * 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, instead it avoids these BIOS bugs by allocates addresses
> + * top-down.
> + * 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

                    preferably:        BARs

> + * to fail. The pci_use_e820 check is there as a workaround for these systems.
> + */



thanks.
--
~Randy