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Re: [PATCH 2/4] xen/cache-col: Fix freeing of colouring information
- To: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
- From: Jan Beulich <jbeulich@xxxxxxxx>
- Date: Fri, 25 Jul 2025 08:12:26 +0200
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- Cc: Anthony PERARD <anthony.perard@xxxxxxxxxx>, Michal Orzel <michal.orzel@xxxxxxx>, Julien Grall <julien@xxxxxxx>, Roger Pau Monné <roger.pau@xxxxxxxxxx>, Stefano Stabellini <sstabellini@xxxxxxxxxx>, Carlo Nonato <carlo.nonato@xxxxxxxxxxxxxxx>, Marco Solieri <marco.solieri@xxxxxxxxxxxxxxx>, Xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxxx>
- Delivery-date: Fri, 25 Jul 2025 06:12:36 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 24.07.2025 18:23, Andrew Cooper wrote:
> domain_destroy() is the wrong position to be freeing colouring information.
>
> The comment in context identifies how domain_destroy() can be called multiple
> times on the same domain, leading to a double free of d->llc_colors as it's
> the wrong side of the atomic_cmpxchg() to be made safe.
>
> Furthermore, by freeing d->llc_colors but leaving d->num_llc_colors nonzero,
> alloc_color_heap_page() can in principle use after free.
>
> Make domain_llc_coloring_free() idempotent, zeroing d->num_llc_colors and
> NULL-ing d->llc_colors after freeing, and call it from domain_teardown().
And this pulling earlier is safe because e.g. free_color_heap_page() ->
page_to_llc_color() -> mfn_to_color() don't use the domain's colors array.
That's not a given (and could be different if e.g. per-domain stats were
maintained), so may want mentioning.
> Fixes: 6985aa5e0c3c ("xen: extend domctl interface for cache coloring")
> Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
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