Re: [Xen-devel] [PATCH v2] x86/hvmloader: round up memory BAR size to 4K

[Jason Andryuk <jandryuk@xxxxxxxxx>]

On Fri, Jan 17, 2020 at 6:08 AM Roger Pau Monne <roger.pau@xxxxxxxxxx> wrote:
>
> When placing memory BARs with sizes smaller than 4K multiple memory
> BARs can end up mapped to the same guest physical address, and thus
> won't work correctly.
>
> Round up all memory BAR sizes to be at least 4K, so that they are
> naturally aligned to a page size and thus don't end up sharing a page.
> Also add a couple of asserts to the current code to make sure the MMIO
> hole is properly sized and aligned.
>
> Note that the guest can still move the BARs around and create this
> collisions, and that BARs not filling up a physical page might leak
> access to other MMIO regions placed in the same host physical page.
>
> This is however no worse than what's currently done, and hence should
> be considered an improvement over the current state.
>
> Reported-by: Jason Andryuk <jandryuk@xxxxxxxxx>
> Signed-off-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
> ---
> Cc: Jason Andryuk <jandryuk@xxxxxxxxx>
> ---
> Changes since v1:
>  - Do the round up when sizing the BARs, so that the MMIO hole is
>    correctly sized.
>  - Add some asserts that the hole is properly sized and size-aligned.
>  - Dropped Jason Tested-by since the code has changed.
> ---
> Jason, can you give this a spin? Thanks.

Tested-by: Jason Andryuk <jandryuk@xxxxxxxxx>

Thanks!

-Jason

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