From: Song Liu <songliubraving@fb.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Song Liu <song@kernel.org>, bpf <bpf@vger.kernel.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"linux-mm@kvack.org" <linux-mm@kvack.org>,
"linux-modules@vger.kernel.org" <linux-modules@vger.kernel.org>,
"mcgrof@kernel.org" <mcgrof@kernel.org>,
"rostedt@goodmis.org" <rostedt@goodmis.org>,
"tglx@linutronix.de" <tglx@linutronix.de>,
"mingo@redhat.com" <mingo@redhat.com>,
"bp@alien8.de" <bp@alien8.de>,
"mhiramat@kernel.org" <mhiramat@kernel.org>,
"naveen.n.rao@linux.ibm.com" <naveen.n.rao@linux.ibm.com>,
"davem@davemloft.net" <davem@davemloft.net>,
"anil.s.keshavamurthy@intel.com" <anil.s.keshavamurthy@intel.com>,
"keescook@chromium.org" <keescook@chromium.org>,
"hch@infradead.org" <hch@infradead.org>,
"dave@stgolabs.net" <dave@stgolabs.net>,
"daniel@iogearbox.net" <daniel@iogearbox.net>,
Kernel Team <Kernel-team@fb.com>,
"x86@kernel.org" <x86@kernel.org>,
"dave.hansen@linux.intel.com" <dave.hansen@linux.intel.com>,
"rick.p.edgecombe@intel.com" <rick.p.edgecombe@intel.com>,
"akpm@linux-foundation.org" <akpm@linux-foundation.org>
Subject: Re: [PATCH bpf-next 1/3] mm/vmalloc: introduce vmalloc_exec which allocates RO+X memory
Date: Fri, 5 Aug 2022 05:29:51 +0000 [thread overview]
Message-ID: <DC201D0D-E51B-42D7-9B3F-194D929A5E9C@fb.com> (raw)
In-Reply-To: <Ys6cWUMHO8XwyYgr@hirez.programming.kicks-ass.net>
Hi Peter,
> On Jul 13, 2022, at 3:20 AM, Peter Zijlstra <peterz@infradead.org> 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.
>
> Start by adding VM_TOPDOWN_VMAP, which instead of returning the lowest
> (leftmost) vmap_area that fits, picks the higests (rightmost).
>
> Then add module_alloc_data() that uses VM_TOPDOWN_VMAP and make
> ARCH_WANTS_MODULE_DATA_IN_VMALLOC use that instead of vmalloc (with a
> weak function doing the vmalloc).
>
> This gets you bottom of module range is RO+X only, top is shattered
> between different !X types.
>
> Then track the boundary between X and !X and ensure module_alloc_data()
> and module_alloc() never cross over and stay strictly separated.
>
> Then change all module_alloc() users to expect RO+X memory, instead of
> RW.
>
> Then make sure any extention of the X range is 2M aligned.
>
> And presto, *everybody* always uses 2M TLB for text, modules, bpf,
> ftrace, the lot and nobody is tracking chunks.
>
> Maybe migration can be eased by instead providing module_alloc_text()
> and ARCH_WANTS_MODULE_ALLOC_TEXT.
I finally got some time to look into the code. A few questions:
1. AFAICT, vmap_area tree only works with PAGE_SIZE aligned addresses.
For the sharing to be more efficient, I think we need to go with
smaller granularity. Will this work? Shall we pick a smaller
granularity, say 64 bytes? Or shall we go all the way to 1 byte?
2. I think we will need multiple vmap_area's sharing the same vm_struct.
Do we need to add refcount to vm_struct?
Thanks,
Song
prev parent reply other threads:[~2022-08-05 5:30 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <20220713071846.3286727-1-song@kernel.org>
[not found] ` <20220713071846.3286727-2-song@kernel.org>
2022-07-13 9:53 ` [PATCH bpf-next 1/3] mm/vmalloc: introduce vmalloc_exec which allocates RO+X memory Peter Zijlstra
2022-07-13 10:08 ` Christoph Hellwig
2022-07-13 15:49 ` Song Liu
2022-07-14 4:23 ` Christoph Hellwig
2022-07-14 4:54 ` Song Liu
2022-07-14 18:15 ` Uladzislau Rezki
2022-07-15 0:24 ` Song Liu
2022-07-13 10:20 ` Peter Zijlstra
2022-07-13 15:48 ` Song Liu
2022-07-13 20:26 ` Peter Zijlstra
2022-07-13 21:20 ` Song Liu
2022-07-14 10:10 ` Peter Zijlstra
2022-07-14 5:16 ` Christoph Hellwig
2022-07-14 7:26 ` Peter Zijlstra
2022-08-05 5:29 ` Song Liu
2022-08-05 5:29 ` Song Liu [this message]
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