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Re: [PATCH] x86/shadow: Drop dubious lastpage diagnostic
- To: "xen-devel@xxxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxxx>
- From: Andrew Cooper <Andrew.Cooper3@xxxxxxxxxx>
- Date: Fri, 20 Jan 2023 14:41:41 +0000
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- Thread-topic: [PATCH] x86/shadow: Drop dubious lastpage diagnostic
On 20/01/2023 2:39 pm, Andrew Cooper wrote:
> 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.
Oh, I see what you mean. Yeah, that will work.
~Andrew
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