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Date: Fri, 19 Apr 2024 22:59:22 +0300
From: Mike Rapoport <rppt@kernel.org>
To: Song Liu <song@kernel.org>
Cc: Mark Rutland <mark.rutland@arm.com>,
	Peter Zijlstra <peterz@infradead.org>, linux-kernel@vger.kernel.org,
	Alexandre Ghiti <alexghiti@rivosinc.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	Bjorn Topel <bjorn@kernel.org>,
	Catalin Marinas <catalin.marinas@arm.com>,
	Christophe Leroy <christophe.leroy@csgroup.eu>,
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	Dinh Nguyen <dinguyen@kernel.org>,
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	Eric Chanudet <echanude@redhat.com>,
	Heiko Carstens <hca@linux.ibm.com>, Helge Deller <deller@gmx.de>,
	Huacai Chen <chenhuacai@kernel.org>,
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	Luis Chamberlain <mcgrof@kernel.org>,
	Michael Ellerman <mpe@ellerman.id.au>,
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Subject: Re: [PATCH v4 05/15] mm: introduce execmem_alloc() and execmem_free()
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In-Reply-To: <CAPhsuW7Nj1Sa_9xQtTgHz9AmX39zdh2x2COqA-qmkfpfX9hNWw@mail.gmail.com>

On Fri, Apr 19, 2024 at 10:32:39AM -0700, Song Liu wrote:
> On Fri, Apr 19, 2024 at 10:03 AM Mike Rapoport <rppt@kernel.org> wrote:
> [...]
> > > >
> > > > [1] https://lore.kernel.org/all/20240411160526.2093408-1-rppt@kernel.org
> > >
> > > For the ROX to work, we need different users (module text, kprobe, etc.) to have
> > > the same execmem_range. From [1]:
> > >
> > > static void *execmem_cache_alloc(struct execmem_range *range, size_t size)
> > > {
> > > ...
> > >        p = __execmem_cache_alloc(size);
> > >        if (p)
> > >                return p;
> > >       err = execmem_cache_populate(range, size);
> > > ...
> > > }
> > >
> > > We are calling __execmem_cache_alloc() without range. For this to work,
> > > we can only call execmem_cache_alloc() with one execmem_range.
> >
> > Actually, on x86 this will "just work" because everything shares the same
> > address space :)
> >
> > The 2M pages in the cache will be in the modules space, so
> > __execmem_cache_alloc() will always return memory from that address space.
> >
> > For other architectures this indeed needs to be fixed with passing the
> > range to __execmem_cache_alloc() and limiting search in the cache for that
> > range.
> 
> I think we at least need the "map to" concept (initially proposed by Thomas)
> to get this work. For example, EXECMEM_BPF and EXECMEM_KPROBE
> maps to EXECMEM_MODULE_TEXT, so that all these actually share
> the same range.

Why?
 
> Does this make sense?
> 
> Song

-- 
Sincerely yours,
Mike.