From: Michael Ellerman <mpe@ellerman.id.au>
To: Linus Torvalds <torvalds@linux-foundation.org>,
Nicholas Piggin <npiggin@gmail.com>
Cc: "Jeff Xu" <jeffxu@google.com>,
"Christophe Leroy" <christophe.leroy@csgroup.eu>,
"Pedro Falcato" <pedro.falcato@gmail.com>,
"kernel test robot" <oliver.sang@intel.com>,
"Jeff Xu" <jeffxu@chromium.org>,
oe-lkp@lists.linux.dev, lkp@intel.com,
linux-kernel@vger.kernel.org,
"Andrew Morton" <akpm@linux-foundation.org>,
"Kees Cook" <keescook@chromium.org>,
"Liam R. Howlett" <Liam.Howlett@oracle.com>,
"Dave Hansen" <dave.hansen@intel.com>,
"Greg Kroah-Hartman" <gregkh@linuxfoundation.org>,
"Guenter Roeck" <groeck@chromium.org>,
"Jann Horn" <jannh@google.com>,
"Jonathan Corbet" <corbet@lwn.net>,
"Jorge Lucangeli Obes" <jorgelo@chromium.org>,
"Matthew Wilcox" <willy@infradead.org>,
"Muhammad Usama Anjum" <usama.anjum@collabora.com>,
"Stephen Röttger" <sroettger@google.com>,
"Suren Baghdasaryan" <surenb@google.com>,
"Amer Al Shanawany" <amer.shanawany@gmail.com>,
"Javier Carrasco" <javier.carrasco.cruz@gmail.com>,
"Shuah Khan" <shuah@kernel.org>,
linux-api@vger.kernel.org, linux-mm@kvack.org,
ying.huang@intel.com, feng.tang@intel.com, fengwei.yin@intel.com
Subject: Re: [linus:master] [mseal] 8be7258aad: stress-ng.pagemove.page_remaps_per_sec -4.4% regression
Date: Tue, 06 Aug 2024 12:01:06 +1000 [thread overview]
Message-ID: <87r0b2if4t.fsf@mail.lhotse> (raw)
In-Reply-To: <CAHk-=wjeWqr+0Ktzbwqrw17aESe5dZm5Kt6nwqtKJX00VsDqWg@mail.gmail.com>
Linus Torvalds <torvalds@linux-foundation.org> writes:
> On Mon, 5 Aug 2024 at 16:25, Nicholas Piggin <npiggin@gmail.com> wrote:
>>
>> Can userspace on other archs not unmap their vdsos?
>
> I think they can, and nobody cares. The "context.vdso" value stays at
> some stale value, and anybody who tries to use it will just fail.
>
> So what makes powerpc special is not "you can unmap the vdso", but
> "powerpc cares".
>
> I just don't quite know _why_ powerpc cares.
AFAIK for CRIU the problem is signal delivery:
arch/powerpc/kernel/signal_64.c:
int handle_rt_signal64(struct ksignal *ksig, sigset_t *set,
struct task_struct *tsk)
{
...
/* Set up to return from userspace. */
if (tsk->mm->context.vdso) {
regs_set_return_ip(regs, VDSO64_SYMBOL(tsk->mm->context.vdso, sigtramp_rt64));
ie. if the VDSO is moved but mm->context.vdso is not updated, signal
delivery will crash in userspace.
x86-64 always uses SA_RESTORER, and arm64 & s390 can use SA_RESTORER, so
I think CRIU uses that to avoid problems with signal delivery when the
VDSO is moved.
riscv doesn't support SA_RESTORER but I guess CRIU doesn't support riscv
yet so it's not become a problem.
There was a patch to support SA_RESTORER on powerpc, but I balked at
merging it because I couldn't find anyone on the glibc side to say
whether they wanted it or not. I guess I should have just merged it.
There was an attempt to unify all the vdso stuff and handle the
VDSO mremap case in generic code:
https://lore.kernel.org/lkml/20210611180242.711399-17-dima@arista.com/
But I think that series got a bit big and complicated and Dmitry had to
move on to other things.
cheers
next prev parent reply other threads:[~2024-08-06 2:01 UTC|newest]
Thread overview: 29+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-08-04 8:59 [linus:master] [mseal] 8be7258aad: stress-ng.pagemove.page_remaps_per_sec -4.4% regression kernel test robot
2024-08-04 20:32 ` Linus Torvalds
2024-08-05 13:33 ` Pedro Falcato
2024-08-05 18:10 ` Jeff Xu
2024-08-05 18:55 ` Linus Torvalds
2024-08-05 19:33 ` Linus Torvalds
2024-08-06 2:14 ` Michael Ellerman
2024-08-06 2:17 ` Linus Torvalds
2024-08-06 12:03 ` Michael Ellerman
2024-08-06 14:43 ` Linus Torvalds
2024-08-07 12:26 ` Michael Ellerman
2024-08-06 6:04 ` Oliver Sang
2024-08-06 14:38 ` Linus Torvalds
2024-08-06 21:37 ` Pedro Falcato
2024-08-07 5:54 ` Oliver Sang
2024-08-05 19:37 ` Jeff Xu
2024-08-05 19:48 ` Linus Torvalds
2024-08-05 19:50 ` Linus Torvalds
2024-08-05 23:24 ` Nicholas Piggin
2024-08-06 0:13 ` Linus Torvalds
2024-08-06 1:22 ` Jeff Xu
2024-08-06 2:01 ` Michael Ellerman [this message]
2024-08-06 2:15 ` Linus Torvalds
2024-09-13 5:47 ` Christophe Leroy
2024-08-05 17:54 ` Jeff Xu
2024-08-05 13:56 ` Jeff Xu
2024-08-05 16:58 ` Jeff Xu
2024-08-06 1:44 ` Oliver Sang
2024-08-06 14:54 ` Jeff Xu
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