Re: [PATCH v3 8/8] PCI/quirks: Avoid certain address on Genoa systems

[Mario Limonciello <mario.limonciello@amd.com>]

On 10/13/26 12:00, Mario Limonciello wrote:
> 
> 
> On 10/13/26 08:09, Ilpo Järvinen wrote:
>> While testing the resource placement changes, tests hit a case where
>> igb fails to probe when BAR 0 is placed at 0x9c000000:
>>
>>     90000000-9cffffff : PCI Bus 0000:a0
>>    -  90000000-902fffff : PCI Bus 0000:a1
>>    -    90000000-900fffff : 0000:a1:00.0
>>    -      90000000-900fffff : igb
>>    -    90100000-901fffff : 0000:a1:00.0
>>    -    90200000-90203fff : 0000:a1:00.0
>>    -      90200000-90203fff : igb
>>    +  9be00000-9c0fffff : PCI Bus 0000:a1
>>    +    9be00000-9befffff : 0000:a1:00.0
>>    +    9bf00000-9bf03fff : 0000:a1:00.0
>>    +    9c000000-9c0fffff : 0000:a1:00.0
>>       9c100000-9c17ffff : amd_iommu
>>       9c180000-9c1803ff : IOAPIC 8
>>
>>    -       Region 0: Memory at 90000000 (32-bit, non-prefetchable) 
>> [size=1M]
>>    -       Region 3: Memory at 90200000 (32-bit, non-prefetchable) 
>> [size=16K]
>>    -       Expansion ROM at 90100000 [disabled] [size=1M]
>>    +       Region 0: Memory at 9c000000 (32-bit, non-prefetchable) 
>> [size=1M]
>>    +       Region 3: Memory at 9bf00000 (32-bit, non-prefetchable) 
>> [size=16K]
>>    +       Expansion ROM at 9be00000 [disabled] [size=1M]
>>
>> igb 0000:a1:00.0 0000:a1:00.0 (uninitialized): PCIe link lost
>> ------------[ cut here ]------------
>> igb: Failed to read reg 0x18!
>> WARNING: drivers/net/ethernet/intel/igb/igb_main.c:724 at 
>> igb_rd32.cold+0x3c/0x4f [igb], CPU#32: kworker/32:1/706
>> ...
>>   igb_get_invariants_82575+0xff/0xf00 [igb]
>>   igb_probe+0x3c8/0x1190 [igb]
>>   local_pci_probe+0x3b/0x80
>>
>> It turns out there is a 64kB iomem black hole at 9c000000 that returns
>> ~0 and this is where igb's BAR 0 resides. If another BAR of the same
>> card is placed into that address, it is similarly black holed.
>>
>> Mark the problematic 64kB range reserved using a quirk bound to the
>> bridge found in the problematic system.
>>
>> Closes: https://bugzilla.kernel.org/show_bug.cgi?id=222074
>> Suggested-by: Mario Limonciello <mario.limonciello@amd.com>
>> Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
>> ---
>> Cc: Borislav Petkov <bp@alien8.de>
>>
>> As an alternative to this, I've also tested reverting the commit
>> 07eab0901ede ("efi/x86: Remove EfiMemoryMappedIO from E820 map") and
>> that also resolves the issue by retaining "9c000000-9cffffff : Reserved"
>> entry in the resource tree.
>>
>> ---
>>   arch/x86/pci/fixup.c | 36 ++++++++++++++++++++++++++++++++++++
>>   1 file changed, 36 insertions(+)
>>
>> diff --git a/arch/x86/pci/fixup.c b/arch/x86/pci/fixup.c
>> index b301c6c8df75..cc463bf492b6 100644
>> --- a/arch/x86/pci/fixup.c
>> +++ b/arch/x86/pci/fixup.c
>> @@ -822,6 +822,42 @@ DECLARE_PCI_FIXUP_RESUME(PCI_VENDOR_ID_AMD, 
>> 0x1571, pci_amd_enable_64bit_bar);
>>   DECLARE_PCI_FIXUP_RESUME(PCI_VENDOR_ID_AMD, 0x15b1, 
>> pci_amd_enable_64bit_bar);
>>   DECLARE_PCI_FIXUP_RESUME(PCI_VENDOR_ID_AMD, 0x1601, 
>> pci_amd_enable_64bit_bar);
>> +/*
>> + * TODO: Remove when/if root cause is found.
>> + *
>> + * Genoa appears to have a 64kB iomem black hole starting at 0x9c000000
>> + * address for which all reads return ~0 blocking an overlapping BAR 
>> from
>> + * working.
>> + *
>> + * Work around the problem by reserving the space prior to making any 
>> iomem
>> + * allocations that could overlap with the black hole.
>> + */
>> +static struct resource genoa_black_hole = 
>> DEFINE_RES_MEM_NAMED(0x9c000000,
>> +                                   SZ_64K,
>> +                                   "reserved");
>> +
>> +static void genoa_iomem_black_hole(struct pci_dev *dev)
>> +{
>> +    struct resource *r;
>> +
>> +    pci_bus_for_each_resource(dev->bus, r) {
>> +        if (!r || !r->flags || !resource_assigned(r))
>> +            continue;
>> +
>> +        if (!__resource_contains_unbound(r, &genoa_black_hole))
>> +            continue;
>> +
>> +        if (resource_assigned(&genoa_black_hole))
>> +            pci_dbg(dev, "iomem black hole workaround already 
>> applied\n");
>> +        else if (!insert_resource(r, &genoa_black_hole))
>> +            pci_info(dev, "iomem black hole workaround enabled\n");
>> +        else
>> +            pci_dbg(dev, "iomem black hole workaround add failed\n");
>> +        return;
>> +    }
>> +}
>> +DECLARE_PCI_FIXUP_HEADER(PCI_VENDOR_ID_AMD, 0x14ab, 
>> genoa_iomem_black_hole);
>> +
>>   #define RS690_LOWER_TOP_OF_DRAM2    0x30
>>   #define RS690_LOWER_TOP_OF_DRAM2_VALID    0x1
>>   #define RS690_UPPER_TOP_OF_DRAM2    0x31
> 
> I guess it's good we know the root cause is 07eab0901ede. If we're going 
> down the path of making holes in that we may well put the hole in 
> efi_remove_e820_mmio() like this (attached).

I don't really like that though.  If Genoa is affected I would expect 
plenty of other machines are too they just haven't been found yet.

Can we roll back 07eab0901ede and add quirks for the busted machines 
instead?