From: "Edgecombe, Rick P" <rick.p.edgecombe@intel.com>
To: "Torvalds, Linus" <torvalds@linux-foundation.org>,
"npiggin@gmail.com" <npiggin@gmail.com>
Cc: "songliubraving@fb.com" <songliubraving@fb.com>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"daniel@iogearbox.net" <daniel@iogearbox.net>,
"hch@infradead.org" <hch@infradead.org>,
"ast@kernel.org" <ast@kernel.org>,
"bpf@vger.kernel.org" <bpf@vger.kernel.org>,
"Kernel-team@fb.com" <Kernel-team@fb.com>,
"linux-mm@kvack.org" <linux-mm@kvack.org>,
"rppt@kernel.org" <rppt@kernel.org>,
"song@kernel.org" <song@kernel.org>,
"pmladek@suse.com" <pmladek@suse.com>,
"akpm@linux-foundation.org" <akpm@linux-foundation.org>,
"hpa@zytor.com" <hpa@zytor.com>,
"edumazet@google.com" <edumazet@google.com>,
"bp@alien8.de" <bp@alien8.de>,
"mcgrof@kernel.org" <mcgrof@kernel.org>,
"mbenes@suse.cz" <mbenes@suse.cz>,
"imbrenda@linux.ibm.com" <imbrenda@linux.ibm.com>
Subject: Re: [PATCH v4 bpf 0/4] vmalloc: bpf: introduce VM_ALLOW_HUGE_VMAP
Date: Fri, 22 Apr 2022 17:10:27 +0000 [thread overview]
Message-ID: <b88a1097c994a72e9d8abfdcc43a4a0f9003d65a.camel@intel.com> (raw)
In-Reply-To: <1650601109.vb3owbt14k.astroid@bobo.none>
On Fri, 2022-04-22 at 14:31 +1000, Nicholas Piggin wrote:
> Any other concerns with the fix?
I had another concern with the vmalloc huge pages. Possibly getting
into paranoid territory here, but it's around the new behavior of
freeing vmalloc page tables. At least on x86 this doesn't happen very
often. AFAICT it all happens during boot or during memory hot unplug.
The risk this entails is racing against all the software page table
walks and walking a freed table. At least on x86 the walks of the
kernel tables are done with no locks, which works because the PTE
updates are atomic and pretty much never freed. Some of the kernel page
table walks in the fault handler are actually triggerable from
userspace.
So it's in the category of "already there is a bug" or a little trouble
someone could cause with a lot of effort. At least until PKS vmalloc
memory shows up. Anyway, as long as we are going over this all again I
thought it was worth bringing up.
next prev parent reply other threads:[~2022-04-22 17:11 UTC|newest]
Thread overview: 55+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <20220415164413.2727220-1-song@kernel.org>
[not found] ` <20220415164413.2727220-2-song@kernel.org>
2022-04-15 17:43 ` [PATCH v4 bpf 1/4] vmalloc: replace VM_NO_HUGE_VMAP with VM_ALLOW_HUGE_VMAP Rik van Riel
[not found] ` <20220415164413.2727220-3-song@kernel.org>
2022-04-15 17:43 ` [PATCH v4 bpf 2/4] page_alloc: use vmalloc_huge for large system hash Rik van Riel
2022-04-25 7:07 ` Geert Uytterhoeven
2022-04-25 8:17 ` Linus Torvalds
2022-04-25 8:24 ` Geert Uytterhoeven
[not found] ` <20220415164413.2727220-4-song@kernel.org>
2022-04-15 18:06 ` [PATCH v4 bpf 3/4] module: introduce module_alloc_huge Rik van Riel
2022-06-16 16:10 ` Dave Hansen
2022-04-15 19:05 ` [PATCH v4 bpf 0/4] vmalloc: bpf: introduce VM_ALLOW_HUGE_VMAP Luis Chamberlain
2022-04-16 1:34 ` Song Liu
2022-04-16 1:42 ` Luis Chamberlain
2022-04-16 1:43 ` Luis Chamberlain
2022-04-16 5:08 ` Christoph Hellwig
2022-04-16 19:55 ` Song Liu
2022-04-16 20:30 ` Linus Torvalds
2022-04-16 22:26 ` Song Liu
2022-04-18 10:06 ` Mike Rapoport
2022-04-19 0:44 ` Luis Chamberlain
2022-04-19 1:56 ` Edgecombe, Rick P
2022-04-19 5:36 ` Song Liu
2022-04-19 18:42 ` Mike Rapoport
2022-04-19 19:20 ` Linus Torvalds
2022-04-20 2:03 ` Alexei Starovoitov
2022-04-20 2:18 ` Linus Torvalds
2022-04-20 14:42 ` Song Liu
2022-04-20 18:28 ` Luis Chamberlain
2022-04-21 3:25 ` Nicholas Piggin
2022-04-21 5:48 ` Linus Torvalds
2022-04-21 6:02 ` Linus Torvalds
2022-04-21 9:07 ` Nicholas Piggin
2022-04-21 8:57 ` Nicholas Piggin
2022-04-21 15:44 ` Linus Torvalds
2022-04-21 23:30 ` Nicholas Piggin
2022-04-22 0:49 ` Linus Torvalds
2022-04-22 1:51 ` Nicholas Piggin
2022-04-22 2:31 ` Linus Torvalds
2022-04-22 2:57 ` Nicholas Piggin
2022-04-21 15:47 ` Edgecombe, Rick P
2022-04-21 16:15 ` Linus Torvalds
2022-04-22 0:12 ` Nicholas Piggin
2022-04-22 2:29 ` Edgecombe, Rick P
2022-04-22 2:47 ` Linus Torvalds
2022-04-22 16:54 ` Edgecombe, Rick P
2022-04-22 3:08 ` Nicholas Piggin
2022-04-22 4:31 ` Nicholas Piggin
2022-04-22 17:10 ` Edgecombe, Rick P [this message]
2022-04-22 20:22 ` Edgecombe, Rick P
2022-04-22 3:33 ` Nicholas Piggin
2022-04-21 9:47 ` Nicholas Piggin
2022-04-19 21:24 ` Luis Chamberlain
2022-04-19 23:58 ` Edgecombe, Rick P
2022-04-20 7:58 ` Petr Mladek
2022-04-19 18:20 ` Mike Rapoport
2022-04-24 17:43 ` Linus Torvalds
2022-04-25 6:48 ` Song Liu
2022-04-21 3:19 ` Nicholas Piggin
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