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Re: [PATCH v8 06/16] xen/memory: Fix mapping grant tables with XENMEM_acquire_resource

  • To: Jan Beulich <jbeulich@xxxxxxxx>
  • From: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
  • Date: Mon, 1 Feb 2021 14:04:31 +0000
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On 01/02/2021 13:03, Jan Beulich wrote:
> On 01.02.2021 12:11, Andrew Cooper wrote:
>> On 01/02/2021 10:10, Roger Pau Monné wrote:
>>> On Sat, Jan 30, 2021 at 02:58:42AM +0000, Andrew Cooper wrote:
>>>> @@ -636,15 +662,45 @@ int compat_memory_op(unsigned int cmd, 
>>>> XEN_GUEST_HANDLE_PARAM(void) compat)
>>>>                      compat_frame_list[i] = frame;
>>>>                  }
>>>> -                if ( __copy_to_compat_offset(cmp.mar.frame_list, 0,
>>>> +                if ( __copy_to_compat_offset(cmp.mar.frame_list, 
>>>> start_extent,
>>>>                                               compat_frame_list,
>>>> -                                             cmp.mar.nr_frames) )
>>>> +                                             done) )
>>>>                      return -EFAULT;
>>> Is it fine to return with a possibly pending continuation already
>>> encoded here?
>>> Other places seem to crash the domain when that happens.
>> Hmm.  This is all a total mess.  (Elsewhere the error handling is also
>> broken - a caller who receives an error can't figure out how to recover)
>> But yes - I think you're right - the only thing we can do here is `goto
>> crash;` and woe betide any 32bit kernel which passes a pointer to a
>> read-only buffer.
> I'd like to ask you to reconsider the "goto crash", both the one
> you mention above and the other one already present in the patch.
> Wiring all the cases where we mean to crash the guest into a
> single domain_crash() invocation has the downside that when
> observing such a case one can't remotely know which path has led
> there. Therefore I'd like to suggest individual domain_crash()
> invocations on every affected path. Elsewhere in the file there
> already is such an instance, commented "Cannot cancel the
> continuation...".

But they're all logically the same, are they not?




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