Re: [PATCH v5 07/10] domain: map/unmap GADDR based shared guest areas

[Julien Grall <julien@xxxxxxx>]

On 02/10/2023 16:11, Roger Pau Monne wrote:
> From: Jan Beulich <jbeulich@xxxxxxxx>
>
> The registration by virtual/linear address has downsides: At least on
> x86 the access is expensive for HVM/PVH domains. Furthermore for 64-bit
> PV domains the areas are inaccessible (and hence cannot be updated by
> Xen) when in guest-user mode, and for HVM guests they may be
> inaccessible when Meltdown mitigations are in place. (There are yet
> more issues.)
>
> In preparation of the introduction of new vCPU operations allowing to
> register the respective areas (one of the two is x86-specific) by
> guest-physical address, flesh out the map/unmap functions.
>
> Noteworthy differences from map_vcpu_info():
> - areas can be registered more than once (and de-registered),
> - remote vCPU-s are paused rather than checked for being down (which in
>    principle can change right after the check),
> - the domain lock is taken for a much smaller region.
>
> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
> Reviewed-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
Reviewed-by: Julien Grall <jgrall@xxxxxxxxxx>

Cheers,

--
Julien Grall