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
