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[pci] Ignore invalid subordinate bus numbers

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Some systems (observed on a Dell C6615) fail to correctly populate the
subordinate PCI bus number on some PCI bridges.  We do not currently
guard against this behaviour, causing us to subsequently scan through
a huge expanse of the PCI bus:dev.fn address range.

Fix by ignoring the subordinate bus number if it is lower than the
bridge's own bus number.

Reported-by: Anisse Astier <an.astier@criteo.com>
Reported-by: Ahmad Mahagna <ahmhad@nvidia.com>
Signed-off-by: Michael Brown <mcb30@ipxe.org>
This commit is contained in:
Michael Brown
2026-02-05 11:58:01 +00:00
parent aa06a76eb8
commit 95e756569a
1 changed files with 14 additions and 7 deletions
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src/drivers/bus/pci.c
+14 -7
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@@ -352,13 +352,20 @@ int pci_find_next ( struct pci_device *pci, uint32_t *busdevfn ) {
hdrtype &= PCI_HEADER_TYPE_MASK;
if ( hdrtype == PCI_HEADER_TYPE_BRIDGE ) {
pci_read_config_byte ( pci, PCI_SUBORDINATE, &sub );
end = PCI_BUSDEVFN ( PCI_SEG ( *busdevfn ),
( sub + 1 ), 0, 0 );
count = ( end - range.start );
if ( count > range.count ) {
DBGC ( pci, PCI_FMT " found subordinate bus "
"%#02x\n", PCI_ARGS ( pci ), sub );
range.count = count;
if ( sub <= PCI_BUS ( *busdevfn ) ) {
DBGC ( pci, PCI_FMT " ignoring invalid "
"subordinate bus %#02x\n",
PCI_ARGS ( pci ), sub );
} else {
end = PCI_BUSDEVFN ( PCI_SEG ( *busdevfn ),
( sub + 1 ), 0, 0 );
count = ( end - range.start );
if ( count > range.count ) {
DBGC ( pci, PCI_FMT " found "
"subordinate bus %#02x\n",
PCI_ARGS ( pci ), sub );
range.count = count;
}
}
}