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Re: [PATCH v4 6/9] domain: map/unmap GADDR based shared guest areas
- To: Roger Pau Monné <roger.pau@xxxxxxxxxx>
- From: Jan Beulich <jbeulich@xxxxxxxx>
- Date: Thu, 28 Sep 2023 12:14:17 +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 10:14:26 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 28.09.2023 12:04, Roger Pau Monné wrote:
> 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, but to be clear: Formally this doesn't help this patch make any
progress, aiui. I'll still need an A-b by a REST maintainer then. An R-b
from you would be different in this regard.
Jan
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