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Re: [PATCH v4] xen/pci: detect when BARs are not suitably positioned
- To: Roger Pau Monne <roger.pau@xxxxxxxxxx>
- From: Jan Beulich <jbeulich@xxxxxxxx>
- Date: Wed, 2 Feb 2022 16:03:57 +0100
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- Cc: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, Wei Liu <wl@xxxxxxx>, George Dunlap <george.dunlap@xxxxxxxxxx>, Julien Grall <julien@xxxxxxx>, Stefano Stabellini <sstabellini@xxxxxxxxxx>, Paul Durrant <paul@xxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxxx
- Delivery-date: Wed, 02 Feb 2022 15:04:17 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 02.02.2022 15:45, Roger Pau Monne wrote:
> One of the boxes where I was attempting to boot Xen in PVH dom0 mode
> has quirky firmware, as it will handover with a PCI device with memory
> decoding enabled and a BAR of size 4K at address 0. Such BAR overlaps
> with a RAM range on the e820.
>
> This interacts badly with the dom0 PVH build, as BARs will be setup on
> the p2m before RAM, so if there's a BAR positioned over a RAM region
> it will trigger a domain crash when the dom0 builder attempts to
> populate that region with a regular RAM page.
>
> It's in general a very bad idea to have a BAR overlapping with any
> memory region defined in the memory map, so add some sanity checks for
> devices that are added with memory decoding enabled in order to assure
> that BARs are not placed on top of memory regions defined in the
> memory map. If overlaps are detected just disable the memory decoding
> bit for the device and expect the hardware domain to properly position
> the BAR.
>
> Note apply_quirks must be called before check_pdev so that ignore_bars
> is set when calling the later. PCI_HEADER_{NORMAL,BRIDGE}_NR_BARS
> needs to be moved into pci_regs.h so it's defined even in the absence
> of vPCI.
>
> Signed-off-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
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