Re: [PATCH v4 6/9] mm/vmalloc: only flush the cache after the vmap succeeded

[Uladzislau Rezki <urezki@gmail.com>]

On Tue, Nov 10, 2026 at 07:25:43PM +0800, Hao Ge wrote:
> vmap_page_range() and __vmap_pages_range() call flush_cache_vmap()
> before they even look at the error code. A failed mapping is never
> used, so the flush is pointless at best.
> 
> According to the Sashiko review it is worse than pointless on UML:
> flush_cache_vmap() there is flush_tlb_kernel_range(), which syncs the
> PTEs into the host OS. Flushing a half-installed mapping therefore
> leaves host mappings behind for a range that was just freed again.
> 
> Only flush when the mapping, and for vmap_page_range() also the KMSAN
> metadata, is fully set up.
> 
> Reported-by: Sashiko <sashiko-bot@kernel.org>
> Signed-off-by: Hao Ge <hao.ge@linux.dev>
> ---
>  mm/vmalloc.c | 8 ++++++--
>  1 file changed, 6 insertions(+), 2 deletions(-)
> 
> diff --git a/mm/vmalloc.c b/mm/vmalloc.c
> index 0565cbfe325c..3f98056f8c7e 100644
> --- a/mm/vmalloc.c
> +++ b/mm/vmalloc.c
> @@ -369,10 +369,12 @@ int vmap_page_range(unsigned long addr, unsigned long end,
>  
>  	err = vmap_range_noflush(addr, end, phys_addr, pgprot_nx(prot),
>  				 ioremap_max_page_shift);
> -	flush_cache_vmap(addr, end);
>  	if (!err)
>  		err = kmsan_ioremap_page_range(addr, end, phys_addr, prot,
>  					       ioremap_max_page_shift);
> +	if (!err)
> +		flush_cache_vmap(addr, end);
> +
>  	return err;
>  }
>  
> @@ -758,7 +760,9 @@ static int __vmap_pages_range(unsigned long addr, unsigned long end,
>  	int err;
>  
>  	err = vmap_pages_range_noflush(addr, end, prot, pages, page_shift, gfp_mask);
> -	flush_cache_vmap(addr, end);
> +	if (!err)
> +		flush_cache_vmap(addr, end);
> +
>  	return err;
>  }
>  
> -- 
> 2.25.1
> 
Like Suren noted, vmap_pages_range_batched() should be fixed also.

--
Uladzislau Rezki