linux-kernel - Re: [PATCH v2 1/3] kho: Adopt KHO radix tree data structures

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Message-ID: <20251024114311.GB847003@nvidia.com>
Date: Fri, 24 Oct 2025 08:43:11 -0300
From: Jason Gunthorpe <jgg@...dia.com>
To: Pasha Tatashin <pasha.tatashin@...een.com>
Cc: Jason Miu <jasonmiu@...gle.com>, Alexander Graf <graf@...zon.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Baoquan He <bhe@...hat.com>, Changyuan Lyu <changyuanl@...gle.com>,
	David Matlack <dmatlack@...gle.com>,
	David Rientjes <rientjes@...gle.com>,
	Mike Rapoport <rppt@...nel.org>,
	Pratyush Yadav <pratyush@...nel.org>, kexec@...ts.infradead.org,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH v2 1/3] kho: Adopt KHO radix tree data structures

On Thu, Oct 23, 2025 at 09:23:30PM -0400, Pasha Tatashin wrote:
> On Thu, Oct 23, 2025 at 7:45 PM Jason Gunthorpe <jgg@...dia.com> wrote:
> >
> > On Mon, Oct 20, 2025 at 03:03:04AM -0700, Jason Miu wrote:
> >
> > > +static struct kho_radix_tree *kho_alloc_radix_tree(void)
> > >  {
> > > +     return (struct kho_radix_tree *)get_zeroed_page(GFP_KERNEL);
> > > +}
> >
> > I was reading the thread over here:
> >
> > https://lore.kernel.org/all/20151222210435.GB20997@ZenIV.linux.org.uk/
> >
> > And I guess this stuff should just use
> >   kzalloc(sizeof(struct kho_radix_tree), GFP_KERNEL);
> 
> kzalloc() uses slab, which in turn may use kfence objects, and kfence
> can allocate memory from KHO scratch area, leading to memory
> corruptions. Let's not use slab allocator for KHO preserved and
> metadata memory, it is not a good choice.

That sounds like a nasty subtle problem to have :(

Really should provide a kho allocator API to document these needs!

Jason