Re: [Xen-devel] [PATCH v3 1/8] public / x86: Introduce __HYPERCALL_dm_op...

[Paul Durrant <Paul.Durrant@xxxxxxxxxx>]

> -----Original Message-----
> From: Jan Beulich [mailto:JBeulich@xxxxxxxx]
> Sent: 13 January 2017 10:31
> To: Andrew Cooper <Andrew.Cooper3@xxxxxxxxxx>; Paul Durrant
> <Paul.Durrant@xxxxxxxxxx>
> Cc: Ian Jackson <Ian.Jackson@xxxxxxxxxx>; Jennifer Herbert
> <jennifer.herbert@xxxxxxxxxx>; Wei Liu <wei.liu2@xxxxxxxxxx>; xen-
> devel@xxxxxxxxxxxxxxxxxxxx; Daniel DeGraaf <dgdegra@xxxxxxxxxxxxx>
> Subject: RE: [PATCH v3 1/8] public / x86: Introduce __HYPERCALL_dm_op...
> 
> >>> On 13.01.17 at 10:05, <Paul.Durrant@xxxxxxxxxx> wrote:
> >> From: Jan Beulich [mailto:JBeulich@xxxxxxxx]
> >> Sent: 12 January 2017 16:29
> >> >>> On 12.01.17 at 17:10, <Paul.Durrant@xxxxxxxxxx> wrote:
> >> >> The userspace side should be
> >> >>
> >> >> struct xen_dm_op_buf {
> >> >>     void *h;
> >> >>     size_t size;
> >> >> }
> >> >>
> >> >> which will work sensibly for 32bit and 64bit userspace, and futureproof
> >> >> (for when 128bit turns up).  Its size is also a power of two which
> >> >> avoids alignment issues in the array.
> >> >>
> >> >> The kernel already has to parse this structure anyway, and will know
> the
> >> >> bitness of its userspace process.  We could easily (at this point)
> >> >> require the kernel to turn it into the kernels bitness for forwarding on
> >> >> to Xen, which covers the 32bit userspace under a 64bit kernel problem,
> >> >> in a way which won't break the hypercall ABI when 128bit comes along.
> >>
> >> But that won't cover a 32-bit kernel.
> >>
> >
> > Do we need to care about a 32-bit kernel for a tools-only hypercall? I
> thought
> > a toolstack already had to be (at least) 64-bit to match Xen.
> 
> Why would that be? Didn't XenServer for a long time run with a
> 32-bit Dom0 on top of a 64-bit Xen? See also domctl/sysctl.
> 

Ok, I thought the landscape had changed since then. If that's the case then a 
64 bit handle seems sensible and I guess we have to deal with 128 bit when that 
happens.

  Paul

> Jan


_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxx
https://lists.xen.org/xen-devel