Re: [Xen-devel] [PATCH V3] tools/libxc, xen/x86: Added xc_set_mem_access_multi()

[George Dunlap <george.dunlap@xxxxxxxxxx>]

On 06/09/16 11:16, Ian Jackson wrote:
> Razvan Cojocaru writes ("[PATCH V3] tools/libxc, xen/x86: Added 
> xc_set_mem_access_multi()"):
>> Currently it is only possible to set mem_access restrictions only for
>> a contiguous range of GFNs (or, as a particular case, for a single GFN).
>> This patch introduces a new libxc function taking an array of GFNs.
>> The alternative would be to set each page in turn, using a userspace-HV
>> roundtrip for each call, and triggering a TLB flush per page set.
>>
>> Signed-off-by: Razvan Cojocaru <rcojocaru@xxxxxxxxxxxxxxx>
>> Acked-by: Wei Liu <wei.liu2@xxxxxxxxxx>
> 
> I have no objection with my tools maintainer hat on.  But I have a
> question for you and/or the hypervisor maintainers:
> 
> Could this aim be achieved with a multicall ?  (Can multicalls defer
> the TLB flush?)

Making people go through the process of constructing a multicall
consisting of a huge array of hypercalls which each set restrictions for
a single gfn seems a bit tedious.  We already have other hypercalls
which take arrays of gfns, so even if it could be done in theory, I
don't see a good reason why not to accept something like this.

 -George

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