linux-kernel - Re: [Xen-devel] [PATCH] xen: don't use privcmd_call() from xen_mc

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Message-Id: <5B20EFE102000078001CACD4@prv1-mh.provo.novell.com>
Date:   Wed, 13 Jun 2018 04:20:17 -0600
From:   "Jan Beulich" <JBeulich@...e.com>
To:     "Juergen Gross" <jgross@...e.com>
Cc:     "xen-devel" <xen-devel@...ts.xenproject.org>,
        "Boris Ostrovsky" <boris.ostrovsky@...cle.com>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [Xen-devel] [PATCH] xen: don't use privcmd_call() from
 xen_mc_flush()

>>> On 13.06.18 at 12:05, <JBeulich@...e.com> wrote:
>>>> On 13.06.18 at 11:58, <jgross@...e.com> wrote:
>> Using privcmd_call() for a singleton multicall seems to be wrong, as
>> privcmd_call() is using stac()/clac() to enable hypervisor access to
>> Linux user space.
>> 
>> Add a new xen_single_call() function to be use for that purpose.
>> 
>> Reported-by: Jan Beulich <jbeulich@...e.com>
>> Signed-off-by: Juergen Gross <jgross@...e.com>
> 
> Reviewed-by: Jan Beulich <jbeulich@...e.com>

Actually I've only now realized that this isn't a real problem right now:
PV can't use SMAP (we don't provide a virtualized version of it), and
HVM/PVH can't use multicalls (which may have to change for PVH Dom0,
so having the change in place is helpful anyway), so the whole
in-kernel logic to collect and issue batches should be unreachable there.

But perhaps the commit message would benefit from a little bit of
re-wording.

Jan