Re: [PATCH] x86/paravirt: merge activate_mm and dup_mmap callbacks

[Juergen Gross]

On 16.01.23 05:27, Srivatsa S. Bhat wrote:
> Hi Juergen,
>
> On 1/12/23 7:21 AM, Juergen Gross wrote:
> > The two paravirt callbacks .mmu.activate_mm and .mmu.dup_mmap are
> > sharing the same implementations in all cases: for Xen PV guests they
> > are pinning the PGD of the new mm_struct, and for all other cases
> > they are a NOP.
>
> I was expecting that the duplicated functions xen_activate_mm() and
> xen_dup_mmap() would be merged into a common one, and that both
> .mmu.activate_mm and .mmu.dup_mmap callbacks would be mapped to that
> common implementation for Xen PV.
>
> > So merge them to a common callback .mmu.enter_mmap (in contrast to the
> > corresponding already existing .mmu.exit_mmap).
>
> Instead, this patch seems to be merging the callbacks themselves...
>
> I see that's not an issue right now since there is no other actual
> user for these callbacks. But are we sure that merging the callbacks
> just because the current user (Xen PV) has the same implementation for
> both is a good idea? The callbacks are invoked at distinct points from
> fork/exec, so wouldn't it be valuable to retain that distinction in
> semantics in the callbacks as well?
>
> However, if you believe that two separate callbacks are not really
> required here (because there is no significant difference in what they
> mean, rather than because their callback implementations happen to be
> the same right now), then could you please expand on this and call it
> out in the commit message, please?

Would you be fine with:

  In the end both callbacks are meant to register an address space with the
  underlying hypervisor, so there needs to be only a single callback for that
  purpose.


Juergen

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