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Re: [PATCH v4 6/9] domain: map/unmap GADDR based shared guest areas
- To: Jan Beulich <jbeulich@xxxxxxxx>
- From: Roger Pau Monné <roger.pau@xxxxxxxxxx>
- Date: Thu, 28 Sep 2023 12:04:26 +0200
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- Cc: "xen-devel@xxxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxxx>, Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, George Dunlap <george.dunlap@xxxxxxxxxx>, Julien Grall <julien@xxxxxxx>, Stefano Stabellini <sstabellini@xxxxxxxxxx>, Wei Liu <wl@xxxxxxx>, Henry Wang <Henry.Wang@xxxxxxx>
- Delivery-date: Thu, 28 Sep 2023 10:05:00 +0000
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- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On Thu, Sep 28, 2023 at 09:16:48AM +0200, Jan Beulich wrote:
> 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>
Acked-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
Thanks, Roger.
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