Re: [PATCH v2 0/4] PCI: Continue E820 vs host bridge window saga

Hans de Goede
2022-12-08T20:04:34Z

Hi,

On 12/8/22 20:03, Bjorn Helgaas wrote:
> From: Bjorn Helgaas <bhelgaas@google.com>
>
> 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 large 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.
>
> Changes from v1 to v2:
> - Remove only large (>= 256KB) EfiMemoryMappedIO areas from E820 to avoid
> the Lenovo X1 Carbon suspend/resume problems. This machine includes
> 64KB of non-window space in the PNP0A03 _CRS, and a corresponding
> EfiMemoryMappedIO area seems to be the only clue to avoid it (see
> https://bugzilla.redhat.com/show_bug.cgi?id=2029207). Interdiff below.

Thanks, v2 looks good to me:

Acked-by: Hans de Goede <hdegoede@redhat.com>

for the series.

I have also started a Fedora kernel test-build with this series added
and asked the reporters of the ideapad touchpad + x1 carbon suspend/resume:

https://bugzilla.redhat.com/show_bug.cgi?id=1868899
https://bugzilla.redhat.com/show_bug.cgi?id=2029207

bugs to test.

Regards,

Hans

> Bjorn Helgaas (4):
> efi/x86: Remove EfiMemoryMappedIO from E820 map
> PCI: Skip allocate_resource() if too little space available
> x86/PCI: Tidy E820 removal messages
> x86/PCI: Fix log message typo
>
> arch/x86/kernel/resource.c | 8 +++++--
> arch/x86/pci/acpi.c | 2 +-
> arch/x86/platform/efi/efi.c | 46 +++++++++++++++++++++++++++++++++++++
> drivers/pci/bus.c | 4 ++++
> 4 files changed, 57 insertions(+), 3 deletions(-)
>