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Re: [PATCH v1] page_alloc: assert IRQs are enabled in heap alloc/free
- To: David Vrabel <dvrabel@xxxxxxxxxx>
- From: Jan Beulich <jbeulich@xxxxxxxx>
- Date: Wed, 20 Apr 2022 10:44:05 +0200
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- Cc: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, George Dunlap <george.dunlap@xxxxxxxxxx>, Julien Grall <julien@xxxxxxx>, Stefano Stabellini <sstabellini@xxxxxxxxxx>, Wei Liu <wl@xxxxxxx>, David Vrabel <dvrabel@xxxxxxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxxx
- Delivery-date: Wed, 20 Apr 2022 08:44:24 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 20.04.2022 10:13, David Vrabel wrote:
>
>
> On 20/04/2022 07:26, Jan Beulich wrote:
>> On 19.04.2022 17:01, David Vrabel wrote:
>>> From: David Vrabel <dvrabel@xxxxxxxxxxxx>
>>>
>>> Heap pages can only be safely allocated and freed with interuupts
>>> enabled as they may require a TLB flush which will send IPIs.
>>>
>>> Enhance the assertions in alloc_xenheap_pages() and
>>> alloc_domheap_pages() to check interrupts are enabled. For consistency
>>> the same asserts are used when freeing heap pages.
>>>
>>> As an exception, during early boot when only 1 PCPU is online,
>>> allocations are permitted with interrupts disabled.
>>
>> This exception is tightly coupled with spin lock checking, i.e. the
>> point in time when spin_debug_enable() is called. I think this wants
>> making explicit at least in the code comment, but as a result I also
>> wonder in how far the extended assertions are really worthwhile: Any
>> violation would be detected in check_lock() anyway. Thoughts?
>
> I was caught out by stop_machine_run() disabling both interrupts and
> spin lock debugging when running the action function, so check_lock()
> didn't help in this (admittedly) narrow use case.
Oh, I see - fair point.
Jan
>> Furthermore I'm concerned of Arm not using either SYS_STATE_smp_boot
>> or spin_debug_enable().
>
> David
>
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