linux-kernel - Re: [PATCH 07/32] mm: Bring back vmalloc

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Message-ID: <8f76b8c2-f59d-43fc-9613-bb094e53fb16@lucifer.local>
Date:   Sat, 13 May 2023 14:25:50 +0100
From:   Lorenzo Stoakes <lstoakes@...il.com>
To:     Christoph Hellwig <hch@...radead.org>
Cc:     Kent Overstreet <kent.overstreet@...ux.dev>,
        linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        linux-bcachefs@...r.kernel.org,
        Kent Overstreet <kent.overstreet@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Uladzislau Rezki <urezki@...il.com>, linux-mm@...ck.org
Subject: Re: [PATCH 07/32] mm: Bring back vmalloc_exec

On Tue, May 09, 2023 at 02:12:41PM -0700, Lorenzo Stoakes wrote:
> On Tue, May 09, 2023 at 01:46:09PM -0700, Christoph Hellwig wrote:
> > On Tue, May 09, 2023 at 12:56:32PM -0400, Kent Overstreet wrote:
> > > From: Kent Overstreet <kent.overstreet@...il.com>
> > >
> > > This is needed for bcachefs, which dynamically generates per-btree node
> > > unpack functions.
> >
> > No, we will never add back a way for random code allocating executable
> > memory in kernel space.
>
> Yeah I think I glossed over this aspect a bit as it looks ostensibly like simply
> reinstating a helper function because the code is now used in more than one
> place (at lsf/mm so a little distracted :)
>
> But it being exported is a problem. Perhaps there's another way of acheving the
> same aim without having to do so?

Just to be abundantly clear, my original ack was a mistake (I overlooked
the _exporting_ of the function being as significant as it is and assumed
in an LSF/MM haze that it was simply a refactoring of _already available_
functionality rather than newly providing a means to allocate directly
executable kernel memory).

Exporting this is horrible for the numerous reasons expounded on in this
thread, we need a different solution.

Nacked-by: Lorenzo Stoakes <lstoakes@...il.com>