linux-kernel - Re: [PATCH] mm/vmalloc, mm/kasan: respect gfp mask in kasan_populate

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Message-Id: <20250831122410.fa3dcddb4a11757ebb16b376@linux-foundation.org>
Date: Sun, 31 Aug 2025 12:24:10 -0700
From: Andrew Morton <akpm@...ux-foundation.org>
To: "Uladzislau Rezki (Sony)" <urezki@...il.com>
Cc: linux-mm@...ck.org, Michal Hocko <mhocko@...nel.org>, Baoquan He
 <bhe@...hat.com>, LKML <linux-kernel@...r.kernel.org>,
 stable@...r.kernel.org
Subject: Re: [PATCH] mm/vmalloc, mm/kasan: respect gfp mask in
 kasan_populate_vmalloc()

On Sun, 31 Aug 2025 14:10:58 +0200 "Uladzislau Rezki (Sony)" <urezki@...il.com> wrote:

> kasan_populate_vmalloc() and its helpers ignore the caller's gfp_mask
> and always allocate memory using the hardcoded GFP_KERNEL flag. This
> makes them inconsistent with vmalloc(), which was recently extended to
> support GFP_NOFS and GFP_NOIO allocations.
> 
> Page table allocations performed during shadow population also ignore
> the external gfp_mask. To preserve the intended semantics of GFP_NOFS
> and GFP_NOIO, wrap the apply_to_page_range() calls into the appropriate
> memalloc scope.
> 
> This patch:
>  - Extends kasan_populate_vmalloc() and helpers to take gfp_mask;
>  - Passes gfp_mask down to alloc_pages_bulk() and __get_free_page();
>  - Enforces GFP_NOFS/NOIO semantics with memalloc_*_save()/restore()
>    around apply_to_page_range();
>  - Updates vmalloc.c and percpu allocator call sites accordingly.
> 
> To: Andrey Ryabinin <ryabinin.a.a@...il.com>
> Cc: <stable@...r.kernel.org>
> Fixes: 451769ebb7e7 ("mm/vmalloc: alloc GFP_NO{FS,IO} for vmalloc")
> Signed-off-by: Uladzislau Rezki (Sony) <urezki@...il.com>

Why cc:stable?

To justify this we'll need a description of the userspace visible
effects of the bug please.  We should always provide this information
when fixing something.  Or when adding something.  Basically, all the
time ;)

Thanks.