Re: [Xen-devel] crash on boot with 4.6.1 on fedora 24

[Juergen Gross <jgross@xxxxxxxx>]

On 11/05/16 12:03, Jan Beulich wrote:
>>>> On 11.05.16 at 11:57, <JGross@xxxxxxxx> wrote:
>> On 11/05/16 09:15, Jan Beulich wrote:
>>>>>> On 11.05.16 at 09:00, <JGross@xxxxxxxx> wrote:
>>>> Having a Xen specific pte flag seems to be much more intrusive than
>>>> having an early boot page fault handler consisting of just one line
>>>> being capable to mimic the default handler in just one aspect (see
>>>> attached patch - only compile tested).
>>>
>>> Well, this simple handler may serve the purpose here, but what's
>>> the effect of having it in place on actual #PF (resulting e.g. from
>>> a bug somewhere)? I.e. what diagnostic information will be
>>> available to the developer in that case, now that the hypervisor
>>> won't help out anymore?
>>
>> Good point. As fixup_exception() is returning 0 in this case we can
>> set the #PF handler to NULL again and retry the failing instruction.
>> This will then lead to the same hypervisor handled case as today.
> 
> And how would you mean to set the #PF handler to this tiny one
> again for the next M2P access? You simply can't have both, I'm afraid.

Why would I need another #PF handler after a crash? I meant something
like:

+dotraplinkage void notrace
+xen_do_page_fault(struct pt_regs *regs, unsigned long error_code)
+{
+       if (!fixup_exception(regs, X86_TRAP_PF))
+               set_intr_gate_notrace(X86_TRAP_PF, NULL);
+}


Juergen

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