Subject: Re: [resend] powerpc/64s: fix page table fragment refcount race vs speculative references

From: Michael Ellerman <[email-masked]>
Date: Thu, 9 Aug 2018 00:26:10 +1000 (AEST)

On Fri, 2018-07-27 at 11:48:17 UTC, Nicholas Piggin wrote:
> The page table fragment allocator uses the main page refcount racily
> with respect to speculative references. A customer observed a BUG due
> to page table page refcount underflow in the fragment allocator. This
> can be caused by the fragment allocator set_page_count stomping on a
> speculative reference, and then the speculative failure handler
> decrements the new reference, and the underflow eventually pops when
> the page tables are freed.
> 
> Fix this by using a dedicated field in the struct page for the page
> table fragment allocator.
> 
> Fixes: 5c1f6ee9a31c ("powerpc: Reduce PTE table memory wastage")
> Reviewed-by: Aneesh Kumar K.V <[email-masked]>
> Signed-off-by: Nicholas Piggin <[email-masked]>

Applied to powerpc next, thanks.

https://git.kernel.org/powerpc/c/4231aba000f5a4583dd9f67057aadb

cheers