Re: [PATCH v2 1/5] mm/kmsan: undo the shadow mapping when the origin mapping fails

[Dev Jain]

On 19/10/26 11:15 am, Hao Ge wrote:
> kmsan_vmap_pages_range_noflush() first maps the shadow pages and then
> the origin pages. If the second mapping fails, the first one is left
> mapped, and the callers do not roll it back. The next vmap of the
> same metadata range hits the stale PTEs again and BUG()s on the huge
> mapping path, or gets -EBUSY with a WARN_ON() on the small page one.
> 
> Undo the shadow mapping on that error path, the same way
> kmsan_ioremap_page_range() cleans up after a partial failure.
> __vunmap_range_noflush() only clears the PTEs; nothing has touched
> the shadow mapping, so no TLB flush is needed.
> 
> Fixes: 47ebd0310e89 ("mm: kmsan: handle alloc failures in kmsan_vmap_pages_range_noflush()")
> Cc: stable@xxxxxxxxxxxxxxx
> Reviewed-by: Suren Baghdasaryan <surenb@xxxxxxxxxx>
> Signed-off-by: Hao Ge <hao.ge@xxxxxxxxx>
> ---

Reviewed-by: Dev Jain <dev.jain@xxxxxxx>


>  mm/kmsan/shadow.c | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/mm/kmsan/shadow.c b/mm/kmsan/shadow.c
> index 0c88d89bf0d6..2166086d3dc3 100644
> --- a/mm/kmsan/shadow.c
> +++ b/mm/kmsan/shadow.c
> @@ -258,6 +258,10 @@ int kmsan_vmap_pages_range_noflush(unsigned long start, unsigned long end,
>  					    o_pages, page_shift);
>  	kmsan_leave_runtime();
>  	if (mapped) {
> +		/* Undo the shadow mapping set up above. */
> +		kmsan_enter_runtime();
> +		__vunmap_range_noflush(shadow_start, shadow_end);
> +		kmsan_leave_runtime();
>  		err = mapped;
>  		goto ret;
>  	}