RE: [for-4.15][PATCH v2 1/5] xen/x86: p2m: Don't map the special pages in the IOMMU page-tables

[Paul Durrant <xadimgnik@xxxxxxxxx>]

> -----Original Message-----
> From: Xen-devel <xen-devel-bounces@xxxxxxxxxxxxxxxxxxxx> On Behalf Of Julien 
> Grall
> Sent: 09 February 2021 15:28
> To: xen-devel@xxxxxxxxxxxxxxxxxxxx
> Cc: hongyxia@xxxxxxxxxxxx; iwj@xxxxxxxxxxxxxx; Julien Grall 
> <jgrall@xxxxxxxxxx>; Jan Beulich
> <jbeulich@xxxxxxxx>; Andrew Cooper <andrew.cooper3@xxxxxxxxxx>; Roger Pau 
> Monné
> <roger.pau@xxxxxxxxxx>; Wei Liu <wl@xxxxxxx>
> Subject: [for-4.15][PATCH v2 1/5] xen/x86: p2m: Don't map the special pages 
> in the IOMMU page-tables
> 
> From: Julien Grall <jgrall@xxxxxxxxxx>
> 
> Currently, the IOMMU page-tables will be populated early in the domain
> creation if the hardware is able to virtualize the local APIC. However,
> the IOMMU page tables will not be freed during early failure and will
> result to a leak.
> 
> An assigned device should not need to DMA into the vLAPIC page, so we
> can avoid to map the page in the IOMMU page-tables.
> 
> This statement is also true for any special pages (the vLAPIC page is
> one of them). So to take the opportunity to prevent the mapping for all
> of them.
> 
> Note that:
>     - This is matching the existing behavior with PV guest
>     - This doesn't change the behavior when the P2M is shared with the
>     IOMMU. IOW, the special pages will still be accessibled by the
>     device.
> 
> Suggested-by: Jan Beulich <jbeulich@xxxxxxxx>
> Signed-off-by: Julien Grall <jgrall@xxxxxxxxxx>
> 

Reviewed-by: Paul Durrant <paul@xxxxxxx>