Re: [Xen-devel] [PATCH V6 4/4] x86/altp2m: fix display frozen when switching to a new view early

[Razvan Cojocaru <rcojocaru@xxxxxxxxxxxxxxx>]

On 11/19/18 2:42 PM, Jan Beulich wrote:
>>>> On 16.11.18 at 16:52, <george.dunlap@xxxxxxxxxx> wrote:
>> On 11/16/18 3:05 PM, George Dunlap wrote:
>>> Now take change_type_range.  The global effect of change_type_range
>>> should be that reads of the p2m which happen afterwards should have the
>>> new, changed value.
>>>
>>> In case A, change_type_range will write invalid entries up to
>>> max_remapped_pfn, leaving the range between max_remapped_pfn and
>>> hostp2m->max_mapped_pfn invalid.  When a gfn in this range is read, an
>>> EPT fault will happen, p2m_altp2m_lazy_copy() will be called, and the
>>> new (correct) value copied from the hostp2m.
>>>
>>> In case B, change_type_range will write invalid entries up until
>>> hostp2m->max_mapped_pfn.  When a gfn in this range is accessed, a
>>> MISCONFIG fault will happen, and the correct value will be calculated in
>>> resolve_misconfig.
>>
>> Or, no: resolve_misconfig() will read the current type in the altp2m,
>> which will be p2m_invalid; p2m_recalc_type() will then return
>> p2m_invalid, and then set the entry to a "plain" invalid without the
>> reserved bit set.  Then the fault will happen again, taking the normal
>> HAP fault path (calling p2m_altp2m_lazy_copy()), at which point...
>>
>>> And at this point, I realize that my previous analysis was probably
>>> wrong, because at this point altp2m->max_remapped_gfn will be wrong:
>>> entries above max_remapped_gfn will have become valid without going
>>> through p2m_altp2m_lazy_copy().
>>
>> ...altp2m->max_remapped_gfn will be set appropriately.
>>
>> I think. :-/
> 
> And I think I can follow your analysis now, which in turn means I
> think your two patches are going to help, but for a proper review
> I'd prefer them to be inline in a mail, rather than attachments.

Please see my review of the second patch, which won't work with my series.

Also, the patches George has sent are applicable after my series has
been applied - would you and George like me to append his first patch to
the end of my series, or would we be better off if he sends his patch
first for the current code, and I rebase my series on that?


Thanks,
Razvan

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