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Re: [PATCH 1/2] x86: Perform mem_sharing teardown before paging teardown
- To: Tamas K Lengyel <tamas@xxxxxxxxxxxxx>
- From: Jan Beulich <jbeulich@xxxxxxxx>
- Date: Thu, 16 Feb 2023 09:31:24 +0100
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- Cc: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, Roger Pau Monné <roger.pau@xxxxxxxxxx>, Wei Liu <wl@xxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxxx
- Delivery-date: Thu, 16 Feb 2023 08:32:15 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 15.02.2023 17:29, Tamas K Lengyel wrote:
> On Wed, Feb 15, 2023 at 5:27 AM Jan Beulich <jbeulich@xxxxxxxx> wrote:
>> Did you consider the alternative of adjusting the ASSERT() in question
>> instead? It could reasonably become
>>
>> #ifdef CONFIG_MEM_SHARING
>> ASSERT(!p2m_is_hostp2m(p2m) || !remove_root ||
> !atomic_read(&d->shr_pages));
>> #endif
>>
>> now, I think. That would be less intrusive a change (helpful for
>> backporting), but there may be other (so far unnamed) benefits of pulling
>> ahead the shared memory teardown.
>
> I have a hard time understanding this proposed ASSERT.
It accounts for the various ways p2m_teardown() can (now) be called,
limiting the actual check for no remaining shared pages to the last
of all these invocations (on the host p2m with remove_root=true).
Maybe
/* Limit the check to the final invocation. */
if ( p2m_is_hostp2m(p2m) && remove_root )
ASSERT(!atomic_read(&d->shr_pages));
would make this easier to follow? Another option might be to move
the assertion to paging_final_teardown(), ahead of that specific call
to p2m_teardown().
Jan
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