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Re: hypercalls with 64-bit results

  • To: Juergen Gross <jgross@xxxxxxxx>
  • From: Jan Beulich <jbeulich@xxxxxxxx>
  • Date: Thu, 17 Jun 2021 10:00:16 +0200
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  • Cc: Anthony Perard <anthony.perard@xxxxxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxxx>, Roger Pau Monné <roger.pau@xxxxxxxxxx>, Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, George Dunlap <george.dunlap@xxxxxxxxxx>, Ian Jackson <iwj@xxxxxxxxxxxxxx>, Stefano Stabellini <sstabellini@xxxxxxxxxx>, Julien Grall <julien@xxxxxxx>, Wei Liu <wl@xxxxxxx>, Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>
  • Delivery-date: Thu, 17 Jun 2021 08:00:38 +0000
  • List-id: Xen developer discussion <xen-devel.lists.xenproject.org>

On 17.06.2021 06:55, Juergen Gross wrote:
> On 16.06.21 18:04, Jan Beulich wrote:
>> Since hypercalls from the tool stack are based on ioctl(), and since
>> ioctl() has a return type of "int", I'm afraid there's no way we can
>> deal with this by adjusting function return types in the libraries.
>> Instead we appear to need either a new privcmd ioctl or new XENMEM_*
>> subops (for those cases where potentially large values get returned).
> I think we can just use a multicall in libxc to wrap the affected
> operations.

Hmm, we might, if we're happy for these to then not work in HVM domains
(PVH Dom0, which still is experimental only, or PVH/HVM DomU-s using
the libraries for some purpose), or if we finally wire up multicalls in
the HVM case (there ought to be a reason why they aren't, but I have no
idea what that is).




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