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Re: [PATCH v2] x86: Perform mem_sharing teardown before paging teardown
- To: Tamas K Lengyel <tamas@xxxxxxxxxxxxx>
- From: Jan Beulich <jbeulich@xxxxxxxx>
- Date: Tue, 21 Feb 2023 14:54:25 +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: Tue, 21 Feb 2023 13:54:38 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 15.02.2023 18:07, Tamas K Lengyel wrote:
> An assert failure has been observed in p2m_teardown when performing vm
> forking and then destroying the forked VM (p2m-basic.c:173). The assert
> checks whether the domain's shared pages counter is 0. According to the
> patch that originally added the assert (7bedbbb5c31) the p2m_teardown
> should only happen after mem_sharing already relinquished all shared pages.
>
> In this patch we flip the order in which relinquish ops are called to avoid
> tripping the assert.
>
> Signed-off-by: Tamas K Lengyel <tamas@xxxxxxxxxxxxx>
> Fixes: e7aa55c0aab3 ("x86/p2m: free the paging memory pool preemptively")
Especially considering the backporting requirement I'm disappointed to
find that you haven't extended the description to explain why this
heavier code churn is to be preferred over an adjustment to the offending
assertion. As said in reply to v1 - I'm willing to accept arguments
towards this being better, but I need to know those arguments.
Jan
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