Re: [Xen-devel] [PATCH v3 for-4.10 2/2] x86/mm: fix a potential race condition in modify_xen_mappings().

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 14.11.17 at 07:53, <yu.c.zhang@xxxxxxxxxxxxxxx> wrote:
> In modify_xen_mappings(), a L1/L2 page table shall be freed,
> if all entries of this page table are empty. Corresponding
> L2/L3 PTE will need be cleared in such scenario.
> 
> However, concurrent paging structure modifications on different
> CPUs may cause the L2/L3 PTEs to be already be cleared or set
> to reference a superpage.
> 
> Therefore the logic to enumerate the L1/L2 page table and to
> reset the corresponding L2/L3 PTE need to be protected with
> spinlock. And the _PAGE_PRESENT and _PAGE_PSE flags need be
> checked after the lock is obtained.
> 
> Signed-off-by: Yu Zhang <yu.c.zhang@xxxxxxxxxxxxxxx>

Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>



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