[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [PATCH for-4.17 v3 1/2] pci: do not disable memory decoding for devices
On 27.10.2022 15:23, Roger Pau Monne wrote: > Commit 75cc460a1b added checks to ensure the position of the BARs from > PCI devices don't overlap with regions defined on the memory map. > When there's a collision memory decoding is left disabled for the > device, assuming that dom0 will reposition the BAR if necessary and > enable memory decoding. > > While this would be the case for devices being used by dom0, devices > being used by the firmware itself that have no driver would usually be > left with memory decoding disabled by dom0 if that's the state dom0 > found them in, and thus firmware trying to make use of them will not > function correctly. > > The initial intent of 75cc460a1b was to prevent vPCI from creating > MMIO mappings on the dom0 p2m over regions that would otherwise > already have mappings established. It's my view now that we likely > went too far with 75cc460a1b, and Xen disabling memory decoding of > devices (as buggy as they might be) is harmful, and reduces the set of > hardware on which Xen works. > > This commits reverts most of 75cc460a1b, and instead adds checks to > vPCI in order to prevent misplaced BARs from being added to the > hardware domain p2m. Signaling on whether BARs are mapped is tracked > in the vpci structure, so that misplaced BARs are not mapped, and thus > Xen won't attempt to unmap them when memory decoding is disabled. > > This restores the behavior of Xen for PV dom0 to the state it was > previous to 75cc460a1b, while also introducing a more contained fix > for the vPCI BAR mapping issues. > > Fixes: 75cc460a1b ('xen/pci: detect when BARs are not suitably positioned') > Signed-off-by: Roger Pau Monné <roger.pau@xxxxxxxxxx> Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
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