Re: [PATCH 3/3] x86/PCI: Preserve host bridge windows completely covered by E820

[Hans de Goede <hdegoede@redhat.com>]

Hi Bjorn,

On 3/4/22 04:51, Bjorn Helgaas wrote:
> From: Bjorn Helgaas <bhelgaas@google.com>
> 
> Many folks have reported PCI devices not working.  It could affect any
> device, but most reports are for Thunderbolt controllers on Lenovo Yoga and
> Clevo Barebone laptops and the touchpad on Lenovo IdeaPads.
> 
> In every report, a region in the E820 table entirely encloses a PCI host
> bridge window from _CRS, and because of 4dc2287c1805 ("x86: avoid E820
> regions when allocating address space"), we ignore the entire window,
> preventing us from assigning space to PCI devices.
> 
> For example, the dmesg log [2] from bug report [1] shows:
> 
>   BIOS-e820: [mem 0x000000004bc50000-0x00000000cfffffff] reserved
>   pci_bus 0000:00: root bus resource [mem 0x65400000-0xbfffffff window]
>   pci 0000:00:15.0: BAR 0: no space for [mem size 0x00001000 64bit]
> 
> The efi=debug dmesg log [3] from the same report shows the EFI memory map
> entries that created the E820 map:
> 
>   efi: mem47: [Reserved |   |WB|WT|WC|UC] range=[0x4bc50000-0x5fffffff]
>   efi: mem48: [Reserved |   |WB|  |  |UC] range=[0x60000000-0x60ffffff]
>   efi: mem49: [Reserved |   |  |  |  |  ] range=[0x61000000-0x653fffff]
>   efi: mem50: [MMIO     |RUN|  |  |  |UC] range=[0x65400000-0xcfffffff]
> 
> 4dc2287c1805 ("x86: avoid E820 regions when allocating address space")
> works around issues where _CRS contains non-window address space that can't
> be used for PCI devices.  It does this by removing E820 regions from host
> bridge windows.  But in these reports, the E820 region covers the entire
> window, so 4dc2287c1805 makes it completely unusable.
> 
> Per UEFI v2.8, sec 7.2, the EfiMemoryMappedIO type means:
> 
>   Used by system firmware to request that a memory-mapped IO region be
>   mapped by the OS to a virtual address so it can be accessed by EFI
>   runtime services.
> 
> A host bridge window is definitely a memory-mapped IO region, and EFI
> runtime services may need to access it, so I don't think we can argue that
> this is a firmware defect.
> 
> Instead, change the 4dc2287c1805 strategy so it only removes E820 regions
> when they overlap *part* of a host bridge window on the assumption that a
> partial overlap is really register space, not part of the window proper.
> 
> If an E820 region covers the entire window from _CRS, assume the _CRS
> window is correct and do nothing.
> 
> [1] https://bugzilla.redhat.com/show_bug.cgi?id=1868899
> [2] https://bugzilla.redhat.com/attachment.cgi?id=1711424
> [3] https://bugzilla.redhat.com/attachment.cgi?id=1861407
> 
> BugLink: https://bugzilla.kernel.org/show_bug.cgi?id=206459
> BugLink: https://bugzilla.kernel.org/show_bug.cgi?id=214259
> 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
> Fixes: 4dc2287c1805 ("x86: avoid E820 regions when allocating address space")
> Link: https://lore.kernel.org/r/20220228105259.230903-1-hdegoede@redhat.com
> Based-on-patch-by: Hans de Goede <hdegoede@redhat.com>
> Reported-by: Benoit Grégoire <benoitg@coeus.ca>   # BZ 206459
> Reported-by: wse@tuxedocomputers.com              # BZ 214259
> Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
> ---
>  arch/x86/kernel/resource.c | 11 +++++++++++
>  1 file changed, 11 insertions(+)
> 
> diff --git a/arch/x86/kernel/resource.c b/arch/x86/kernel/resource.c
> index 7378ea146976..405f0af53e3d 100644
> --- a/arch/x86/kernel/resource.c
> +++ b/arch/x86/kernel/resource.c
> @@ -39,6 +39,17 @@ void remove_e820_regions(struct device *dev, struct resource *avail)
>  		e820_start = entry->addr;
>  		e820_end = entry->addr + entry->size - 1;
>  
> +		/*
> +		 * If an E820 entry covers just part of the resource, we
> +		 * assume E820 is telling us about something like host
> +		 * bridge register space that is unavailable for PCI
> +		 * devices.  But if it covers the *entire* resource, it's
> +		 * more likely just telling us that this is MMIO space, and
> +		 * that doesn't need to be removed.
> +		 */
> +		if (e820_start <= avail->start && avail->end <= e820_end)
> +			continue;
> +

IMHO it would be good to add some logging here, since hitting this is
somewhat of a special case. For the Fedora test kernels I did I changed
this to:

		if (e820_start <= avail->start && avail->end <= e820_end) {
			dev_info(dev, "resource %pR fully covered by e820 entry [mem %#010Lx-%#010Lx]\n",
				 avail, e820_start, e820_end);
			continue;
		}

And I expect/hope to see this new info message on the ideapad with the
touchpad issue.

Regards,

Hans



>  		resource_clip(avail, e820_start, e820_end);
>  		if (orig.start != avail->start || orig.end != avail->end) {
>  			dev_info(dev, "clipped %pR to %pR for e820 entry [mem %#010Lx-%#010Lx]\n",