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

[Keir Fraser <keir@xxxxxxx>]

On 10/11/2011 09:54, "Jan Beulich" <JBeulich@xxxxxxxx> wrote:

>>>> On 10.11.11 at 09:44, Jean Guyader <jean.guyader@xxxxxxxxxxxxx> 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?
> 
> 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.

There are plenty of other examples where we check for preemption before
doing any real work (eg. do_mmuext_op, do_mmu_update). I guess checking at
the end of the loop is a little bit better maybe. I'm not very bothered
either way.

 -- Keir

>> --- 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;
>>     }
> 



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