Re: [PATCH v2] x86/vpci: fix handling of BAR overlaps with non-hole regions

[Julien Grall <julien@xxxxxxx>]

Hi Roger,

On 16/05/2025 09:31, Roger Pau Monne wrote:
> For once the message printed when a BAR overlaps with a non-hole regions is
> not accurate on x86.  While the BAR won't be mapped by the vPCI logic, it
> is quite likely overlapping with a reserved region in the memory map, and
> already mapped as by default all reserved regions are identity mapped in
> the p2m.  Fix the message so it just warns about the overlap, without
> mentioning that the BAR won't be mapped, as this has caused confusion in
> the past.
>
> Secondly, when an overlap is detected the BAR 'enabled' field is not set,
> hence other vPCI code that depends on it like vPCI MSI-X handling won't
> function properly, as it sees the BAR as disabled, even when memory
> decoding is enabled for the device and the BAR is likely mapped in the
> p2m.  Change the handling of BARs that overlap non-hole regions to instead
> remove any overlapped regions from the rangeset, so the resulting ranges to
> map just contain the hole regions.  This requires introducing a new
> pci_sanitize_bar_memory() that's implemented per-arch and sanitizes the
> address range to add to the p2m.
>
> For x86 pci_sanitize_bar_memory() removes any regions present in the host
> memory map, for ARM this is currently left as a dummy handler to not change
> existing behavior.
>
> Ultimately the above changes should fix the vPCI MSI-X handlers not working
> correctly when the BAR that contains the MSI-X table overlaps with a
> non-hole region, as then the 'enabled' BAR bit won't be set and the MSI-X
> traps won't handle accesses as expected.
>
> Reported-by: Stefano Stabellini <stefano.stabellini@xxxxxxx>
> Fixes: 53d9133638c3 ('pci: do not disable memory decoding for devices')
> Signed-off-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
> Tested-by: Victor M Lira <victorm.lira@xxxxxxx>
Acked-by: Julien Grall <jgrall@xxxxxxxxxx>

Cheers,

--
Julien Grall