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Re: [PATCH] x86/shadow: Drop dubious lastpage diagnostic
- To: Andrew Cooper <Andrew.Cooper3@xxxxxxxxxx>
- From: Jan Beulich <jbeulich@xxxxxxxx>
- Date: Fri, 20 Jan 2023 15:20:47 +0100
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- Cc: Roger Pau Monne <roger.pau@xxxxxxxxxx>, Wei Liu <wl@xxxxxxx>, George Dunlap <George.Dunlap@xxxxxxxxxx>, "Tim (Xen.org)" <tim@xxxxxxx>, Xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxxx>
- Delivery-date: Fri, 20 Jan 2023 14:20:59 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 20.01.2023 15:10, Andrew Cooper wrote:
> On 20/01/2023 1:10 pm, Jan Beulich wrote:
>> On 20.01.2023 12:45, Andrew Cooper wrote:
>>> This is a global variable (actually 3, one per GUEST_PAGING_LEVEL), operated
>>> on using atomics only (with no regard to what else shares the same
>>> cacheline),
>>> which emits a diagnostic (in debug builds only) without changing any program
>>> behaviour.
>>>
>>> Based on read-only p2m types including logdirty, this diagnostic can be
>>> tripped by entirely legitimate guest behaviour.
>> Can it? At the very least shadow doesn't use p2m_ram_logdirty, but "cooks"
>> log-dirty handling its own way.
>>
>>> Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
>> Acked-by: Jan Beulich <jbeulich@xxxxxxxx>
>
> Thanks.
>
>> with the last sentence above corrected (if need be: removed).
>
> I can remove it, but I feel as if there ought to be something there.
>
> The other RO types are ram_ro, grant_map_ro and ram_shared. shared has
> hopefully been unshared before getting to this point, while the other
> two have unclear semantics (as neither exist in real systems).
I'd be okay as long as the "including logdirty" part isn't there. If
we're unsure, perhaps then also instead of "can" either "might" or
"can possibly"?
Jan
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