Re: [PATCH v3] xen/arm: pci: fix check in pci_check_bar()

[Julien Grall <julien@xxxxxxx>]

On 12/07/2023 18:04, Rahul Singh wrote:
> Hi Stewart,
>
> > On 12 Jul 2023, at 2:52 pm, Stewart Hildebrand <Stewart.Hildebrand@xxxxxxx> 
> > wrote:
> >
> > When mapping BARs for vPCI, it's valid for a BAR mfn_t start to equal the BAR
> > mfn_t end (i.e. start == end) since end is inclusive. However, pci_check_bar()
> > currently returns false in this case, which results in Xen not mapping the BAR
> > in the guest 2nd stage page tables. In this example boot log, Linux has mapped
> > the BARs in the 1st stage, but since Xen did not map them in the 2nd stage,
> > Linux encounters a data abort and panics:
> >
> > [    2.593300] pci 0000:00:00.0: BAR 0: assigned [mem 0x50008000-0x50008fff]
> > [    2.593682] pci 0000:00:00.0: BAR 2: assigned [mem 0x50009000-0x50009fff]
> > [    2.594066] pci 0000:00:00.0: BAR 4: assigned [mem 0x5000a000-0x5000afff]
> > ...
> > [    2.810502] virtio-pci 0000:00:00.0: enabling device (0000 -> 0002)
> > (XEN) 0000:00:00.0: not mapping BAR [50008, 50008] invalid position
> > (XEN) 0000:00:00.0: not mapping BAR [50009, 50009] invalid position
> > (XEN) 0000:00:00.0: not mapping BAR [5000a, 5000a] invalid position
> > [    2.817502] virtio-pci 0000:00:00.0: virtio_pci: leaving for legacy driver
> > [    2.817853] virtio-pci 0000:00:00.0: enabling bus mastering
> > (XEN) arch/arm/traps.c:1992:d0v0 HSR=0x00000093010045 pc=0xffff8000089507d4 
> > gva=0xffff80000c46d012 gpa=0x00000050008012
> > [    2.818397] Unable to handle kernel ttbr address size fault at virtual 
> > address ffff80000c46d012
> > ...
> >
> > Adjust the end physical address e to account for the full page when converting
> > from mfn, at which point s and e cannot be equal, so drop the equality check in
> > the condition.
> >
> > Note that adjusting e to account for the full page also increases the accuracy
> > of the subsequent is_bar_valid check.
> >
> > Fixes: cc80e2bab0d0 ("xen/pci: replace call to is_memory_hole to pci_check_bar")
> > Signed-off-by: Stewart Hildebrand <stewart.hildebrand@xxxxxxx>
> > Reviewed-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
> I tested the patch on N1SDP board everything works.
>
> Reviewed-by: Rahul Singh <rahul.singh@xxxxxxx>
> Tested-by: Rahul Singh <rahul.singh@xxxxxxx>
Acked-by: Julien Grall <jgrall@xxxxxxxxxx>

> Regards,
> Rahul
--
Julien Grall