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

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Message-ID: <aLVuw2UkYUcL_Oi0@pc638.lan>
Date: Mon, 1 Sep 2025 12:00:35 +0200
From: Uladzislau Rezki <urezki@...il.com>
To: Andrew Morton <akpm@...ux-foundation.org>
Cc: "Uladzislau Rezki (Sony)" <urezki@...il.com>, 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, Aug 31, 2025 at 12:24:10PM -0700, Andrew Morton wrote:
> 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 ;)
> 
Yes, i am not aware about any report. I was thinking more about that
"mm/vmalloc: alloc GFP_NO{FS,IO} for vmalloc" was incomplete and thus
is a good candidate for stable.

We can drop it for the stable until there are some reports from people.
If there are :)

Thanks!

--
Uladzislau Rezki