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Howlett" , Dave Hansen , Greg Kroah-Hartman , Guenter Roeck , Jann Horn , Jonathan Corbet , Jorge Lucangeli Obes , Matthew Wilcox , Muhammad Usama Anjum , Stephen =?utf-8?Q?R?= =?utf-8?Q?=C3=B6ttger?= , Suren Baghdasaryan , Amer Al Shanawany , Javier Carrasco , Shuah Khan , 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 In-Reply-To: References: <202408041602.caa0372-oliver.sang@intel.com> Date: Tue, 06 Aug 2024 12:01:06 +1000 Message-ID: <87r0b2if4t.fsf@mail.lhotse> MIME-Version: 1.0 Content-Type: text/plain X-Rspam-User: X-Rspamd-Queue-Id: 92355140008 X-Rspamd-Server: rspam01 X-Stat-Signature: 8iojjmjautamkj3b5y57zxk3r6cuobeb X-HE-Tag: 1722909674-473723 X-HE-Meta: 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 Jj+jogbm 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: Linus Torvalds writes: > On Mon, 5 Aug 2024 at 16:25, Nicholas Piggin 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