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Re: [PATCH] x86/shadow: Drop dubious lastpage diagnostic
- To: Jan Beulich <jbeulich@xxxxxxxx>
- From: Andrew Cooper <Andrew.Cooper3@xxxxxxxxxx>
- Date: Fri, 20 Jan 2023 14:39:47 +0000
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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>
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- Thread-topic: [PATCH] x86/shadow: Drop dubious lastpage diagnostic
On 20/01/2023 2:20 pm, Jan Beulich wrote:
> 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"?
I'll just delete it. It's not important enough for the time it's taking.
~Andrew
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