Hi
Am 04.12.22 um 10:29 schrieb Hans de Goede:
Hi Bjorn,
On 12/3/22 18:57, Bjorn Helgaas wrote:
On Sat, Dec 03, 2022 at 01:44:10PM +0100, Hans de Goede wrote:
Hi Bjorn,
On 12/2/22 22:18, Bjorn Helgaas wrote:
From: Bjorn Helgaas <bhelgaas@xxxxxxxxxx>
When allocating space for PCI BARs, Linux avoids allocating space mentioned
in the E820 map. This was originally done by 4dc2287c1805 ("x86: avoid
E820 regions when allocating address space") to work around BIOS defects
that included unusable space in host bridge _CRS.
Some recent machines use EfiMemoryMappedIO for PCI MMCONFIG and host bridge
apertures, and bootloaders and EFI stubs convert those to E820 regions,
which means we can't allocate space for hot-added PCI devices (often a
dock) or for devices the BIOS didn't configure (often a touchpad)
The current strategy is to add DMI quirks that disable the E820 filtering
on these machines and to disable it entirely starting with 2023 BIOSes:
d341838d776a ("x86/PCI: Disable E820 reserved region clipping via quirks")
0ae084d5a674 ("x86/PCI: Disable E820 reserved region clipping starting in 2023")
But the quirks are problematic because it's really hard to list all the
machines that need them.
This series is an attempt at a more generic approach. I'm told by firmware
folks that EfiMemoryMappedIO means "the OS should map this area so EFI
runtime services can use it in virtual mode," but does not prevent the OS
from using it.
The first patch removes any EfiMemoryMappedIO areas from the E820 map.
This doesn't affect any virtual mapping of those areas (that would have to
be done directly from the EFI memory map) but it means Linux can allocate
space for PCI MMIO.
The rest are basically cosmetic log message changes.
Thank you for working on this. I'm a bit worried about this series though.
The 2 things which I worry about are:
1. I think this will not help when people boot in BIOS (CSM) mode rather
then UEFI mode which quite a few Linux users still do because they learned
to do this years ago when Linux EFI support (and EFI fw itself) was still
a bit in flux.
IIRC from the last time we looked at this in CSM mode the BIOS itself
translates the EfiMemoryMappedIO areas to reserved E820 regions. So when
people use the BIOS CSM mode to boot, then this patch will not help
since the kernel lacks the info to do the translation.
Right, if BIOS CSM puts EfiMemoryMappedIO in the E820 map the same way
bootloaders do, and the kernel doesn't have the EFI memory map, this
series won't help.
So I just got the requested dmesg in BIOS CSM mode from:
https://bugzilla.redhat.com/show_bug.cgi?id=1868899
And it says:
[ 0.000000] BIOS-e820: [mem 0x000000004bc50000-0x00000000cfffffff] reserved
[ 0.316140] pci_bus 0000:00: root bus resource [mem 0x65400000-0xbfffffff window]
So I'm afraid that I remembered correctly and the CSM adds
the EfiMemoryMappedIO regions to the E820 map as reserved :(
So as you said, this series won't help for people booting in
BIOS compatibility mode. Which means that we should at least keep
the current list of no_e820 quirks to avoid regressing those models
when booted in BIOS compatibility mode.
And maybe still add at least the Clevo model for which I recently
submitted a new no_e820 quirk so that that will work in BIOS CSM
mode too ?
Do you mean the X170KM-G? I don't think it has the option to switch to Legacy
BIOS mode (At least i didn't found an option in the bios version i have)
Note I know you did not propose to drop the quirks in this series,
just covering all the bases here.
Regards,
Hans
Kind regards,
Werner Sembach
