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Date:   Tue, 9 May 2023 14:43:19 -0700
From:   "Darrick J. Wong" <djwong@kernel.org>
To:     Lorenzo Stoakes <lstoakes@gmail.com>
Cc:     Christoph Hellwig <hch@infradead.org>,
        Kent Overstreet <kent.overstreet@linux.dev>,
        linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org,
        linux-bcachefs@vger.kernel.org,
        Kent Overstreet <kent.overstreet@gmail.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Uladzislau Rezki <urezki@gmail.com>, linux-mm@kvack.org
Subject: Re: [PATCH 07/32] mm: Bring back vmalloc_exec
Message-ID: <20230509214319.GA858791@frogsfrogsfrogs>
References: <20230509165657.1735798-1-kent.overstreet@linux.dev>
 <20230509165657.1735798-8-kent.overstreet@linux.dev>
 <ZFqxEWqD19eHe353@infradead.org>
 <ZFq3SdSBJ_LWsOgd@murray>
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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@gmail.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?

I already trolled Kent with this on IRC, but for the parts of bcachefs
that want better assembly code than whatever gcc generates from the C
source, could you compile code to BPF and then let the BPF JIT engines
turn that into machine code for you?

(also distracted by LSFMM)

--D