linux-kernel - Re: [PATCH bpf-next 1/3] mm/vmalloc: introduce vmalloc

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Message-ID: <78A18945-0841-4CCE-8A33-6C09ECBFF7E1@fb.com>
Date:   Wed, 13 Jul 2022 21:20:55 +0000
From:   Song Liu <songliubraving@...com>
To:     Peter Zijlstra <peterz@...radead.org>
CC:     Song Liu <song@...nel.org>, bpf <bpf@...r.kernel.org>,
        lkml <linux-kernel@...r.kernel.org>,
        Linux-MM <linux-mm@...ck.org>,
        "linux-modules@...r.kernel.org" <linux-modules@...r.kernel.org>,
        Luis Chamberlain <mcgrof@...nel.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        "naveen.n.rao@...ux.ibm.com" <naveen.n.rao@...ux.ibm.com>,
        "davem@...emloft.net" <davem@...emloft.net>,
        "anil.s.keshavamurthy@...el.com" <anil.s.keshavamurthy@...el.com>,
        "keescook@...omium.org" <keescook@...omium.org>,
        "hch@...radead.org" <hch@...radead.org>,
        "dave@...olabs.net" <dave@...olabs.net>,
        "daniel@...earbox.net" <daniel@...earbox.net>,
        Kernel Team <Kernel-team@...com>,
        "x86@...nel.org" <x86@...nel.org>,
        "dave.hansen@...ux.intel.com" <dave.hansen@...ux.intel.com>,
        "rick.p.edgecombe@...el.com" <rick.p.edgecombe@...el.com>,
        "akpm@...ux-foundation.org" <akpm@...ux-foundation.org>
Subject: Re: [PATCH bpf-next 1/3] mm/vmalloc: introduce vmalloc_exec which
 allocates RO+X memory



> On Jul 13, 2022, at 1:26 PM, Peter Zijlstra <peterz@...radead.org> wrote:
> 
> On Wed, Jul 13, 2022 at 03:48:35PM +0000, Song Liu wrote:
> 
>>> So how about instead we separate them? Then much of the problem goes
>>> away, you don't need to track these 2M chunks at all.
>> 
>> If we manage the memory in < 2MiB granularity, either 4kB or smaller, 
>> we still need some way to track which parts are being used, no? I mean
>> the bitmap.  
> 
> I was thinking the vmalloc vmap_area tree could help out there.

Interesting. vmap_area tree indeed keeps a lot of useful information. 

Currently, powerpc supports CONFIG_ARCH_WANTS_MODULES_DATA_IN_VMALLOC, 
which leaves module_alloc just for module text. If this works, we get
separation between RO+X and RW memory. What would it take to enable
CONFIG_ARCH_WANTS_MODULES_DATA_IN_VMALLOC for x86_64? 

Thanks,
Song