* Taming "BIOS assigned incorrect VT-d unit" warning?
@ 2016-06-14 13:56 Denys Vlasenko
0 siblings, 0 replies; only message in thread
From: Denys Vlasenko @ 2016-06-14 13:56 UTC (permalink / raw)
To: Linux Kernel Mailing List
I'm are getting some user reports with this warning:
static void quirk_ioat_snb_local_iommu(struct pci_dev *pdev)
{
...
rc = pci_bus_read_config_dword(pdev->bus, PCI_DEVFN(0, 0),
0xb0, &vtbar);
vtbar &= 0xffff0000;
/* we know that the this iommu should be at offset 0xa000 from vtbar */
drhd = dmar_find_matched_drhd_unit(pdev);
if (WARN_TAINT_ONCE(!drhd || drhd->reg_base_addr - vtbar != 0xa000,
TAINT_FIRMWARE_WORKAROUND,
"BIOS assigned incorrect VT-d unit for
Intel(R) QuickData Technology device\n"))
pdev->dev.archdata.iommu = DUMMY_DEVICE_DOMAIN_INFO;
}
I experimented a bit and found out that on their machine,
dmar_find_matched_drhd_unit(pdev) returns NULL.
That is, in their case it's not known that
drhd->reg_base_addr - vtbar is wrong.
The warning is actually not true.
I tried a patch
drhd = dmar_find_matched_drhd_unit(pdev);
+ if (!drhd)
+ return;
and the affected machine works after it.
I'm not too familiar with this code.
Is dmar_find_matched_drhd_unit(pdev) == NULL normal?
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2016-06-14 13:56 Taming "BIOS assigned incorrect VT-d unit" warning? Denys Vlasenko
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