Re: [PATCH 4/6] mm: New XENMEM space, XENMAPSPACE_gmfn_range

[Tim Deegan <tim@xen.org>]

At 09:54 +0000 on 10 Nov (1320918887), Jan Beulich wrote:
> >>> On 10.11.11 at 09:44, Jean Guyader <jean.guyader@eu.citrix.com> wrote:
> 
> In the native implementation I neither see the XENMAPSPACE_gmfn_range
> case getting actually handled in the main switch (did you mean to change
> xatp.space to XENMAPSPACE_gmfn in that case?), nor do I see how you
> communicate back how many of the pages were successfully processed in
> the event of an error in the middle of the processing or when a
> continuation is required.
> 
> But with the patch being pretty hard to read, maybe I'm simply
> overlooking something?

The patch changes the (compat-translated) hypercall arguments in place to
reflect what's been done.  Agreed that it's particularly hard to read,
though. 

Tim.

> Further (I realize I should have commented on this earlier) I think that
> in order to allow forward progress you should not check for preemption
> on the very first iteration of each (re-)invocation. That would also
> guarantee no behavioral change to the original single-page variants.
> 
> >--- a/xen/arch/x86/x86_64/compat/mm.c
> >+++ b/xen/arch/x86/x86_64/compat/mm.c
> >@@ -63,6 +63,16 @@ int compat_arch_memory_op(int op, XEN_GUEST_HANDLE(void) arg)
> > 
> >         XLAT_add_to_physmap(nat, &cmp);
> >         rc = arch_memory_op(op, guest_handle_from_ptr(nat, void));
> >+        if ( rc < 0 )
> >+            return rc;
> >+
> >+        if ( rc == __HYPERVISOR_memory_op )
> >+            hypercall_xlat_continuation(NULL, 0x2, nat, arg);
> >+
> >+        XLAT_add_to_physmap(&cmp, nat);
> >+
> >+        if ( copy_to_guest(arg, &cmp, 1) )
> >+            return -EFAULT;
> 
> Other than in the XENMEM_[gs]et_pod_target you (so far, subject to the
> above comment resulting in a behavioral change) don't have any real
> outputs here, and hence there's no need to always to the outbound
> translation - i.e. all of this could be moved into the if ()'s body.
> 
> Jan
> 
> > 
> >         break;
> >     }
>