From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail.windriver.com ([147.11.1.11]:43824 "EHLO mail.windriver.com" rhost-flags-OK-OK-OK-OK) by eddie.linux-mips.org with ESMTP id S23991359AbdCGMGHhJyPd (ORCPT ); Tue, 7 Mar 2017 13:06:07 +0100 Subject: Re: [PATCH] MIPS: reset all task's asid to 0 after asid_cache(cpu) overflows References: <1488684260-18867-1-git-send-email-jiwei.sun@windriver.com> <6054d364-5095-d13b-ebf8-a7b6bf8b2024@cogentembedded.com> <58BD0E0A.9000402@windriver.com> <702ff6e3-9bc7-755b-56ec-86394d959230@cogentembedded.com> From: Jiwei Sun Message-ID: <58BEA251.9070200@windriver.com> Date: Tue, 7 Mar 2017 20:06:41 +0800 MIME-Version: 1.0 In-Reply-To: <702ff6e3-9bc7-755b-56ec-86394d959230@cogentembedded.com> Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit Return-Path: Sender: linux-mips-bounce@linux-mips.org Errors-to: linux-mips-bounce@linux-mips.org List-help: List-unsubscribe: List-software: Ecartis version 1.0.0 List-subscribe: List-owner: List-post: List-archive: To: Sergei Shtylyov Cc: linux-mips@linux-mips.org, linux-kernel@vger.kernel.org, jiwei.sun.bj@qq.com Message-ID: <20170307120641.hcm1CDuKMIBivhQgFoIFpxt5S4ocxuyrcnpjxXx-mEc@z> On 03/06/2017 04:34 PM, Sergei Shtylyov wrote: > On 3/6/2017 10:21 AM, jsun4 wrote: > >>>> If asid_cache(cpu) overflows, there may be two tasks with the same >>>> asid. It is a risk that the two different tasks may have the same >>>> address space. >>>> >>>> A process will update its asid to newer version only when switch_mm() >>>> is called and matches the following condition: >>>> if ((cpu_context(cpu, next) ^ asid_cache(cpu)) >>>> & asid_version_mask(cpu)) >>>> get_new_mmu_context(next, cpu); >>>> If asid_cache(cpu) overflows, cpu_context(cpu,next) and asid_cache(cpu) >>>> will be reset to asid_first_version(cpu), and start a new cycle. It >>>> can result in two tasks that have the same ASID in the process list. >>>> >>>> For example, in CONFIG_CPU_MIPS32_R2, task named A's asid on CPU1 is >>>> 0x100, and has been sleeping and been not scheduled. After a long period >>>> of time, another running task named B's asid on CPU1 is 0xffffffff, and >>>> asid cached in the CPU1 is 0xffffffff too, next task named C is forked, >>>> when schedule from B to C on CPU1, asid_cache(cpu) will overflow, so C's >>>> asid on CPU1 will be 0x100 according to get_new_mmu_context(). A's asid >>>> is the same as C, if now A is rescheduled on CPU1, A's asid is not able >>>> to renew according to 'if' clause, and the local TLB entry can't be >>>> flushed too, A's address space will be the same as C. >>>> >>>> If asid_cache(cpu) overflows, all of user space task's asid on this CPU >>>> are able to set a invalid value (such as 0), it will avoid the risk. >>>> >>>> Signed-off-by: Jiwei Sun >>>> --- >>>> arch/mips/include/asm/mmu_context.h | 9 ++++++++- >>>> 1 file changed, 8 insertions(+), 1 deletion(-) >>>> >>>> diff --git a/arch/mips/include/asm/mmu_context.h b/arch/mips/include/asm/mmu_context.h >>>> index ddd57ad..1f60efc 100644 >>>> --- a/arch/mips/include/asm/mmu_context.h >>>> +++ b/arch/mips/include/asm/mmu_context.h >>>> @@ -108,8 +108,15 @@ static inline void enter_lazy_tlb(struct mm_struct *mm, struct task_struct *tsk) >>>> #else >>>> local_flush_tlb_all(); /* start new asid cycle */ >>>> #endif >>>> - if (!asid) /* fix version if needed */ >>>> + if (!asid) { /* fix version if needed */ >>>> + struct task_struct *p; >>>> + >>>> + for_each_process(p) { >>>> + if ((p->mm)) >>> >>> Why double parens? >> >> At the beginning, the code was written as following >> if ((p->mm) && (p->mm != mm)) >> cpu_context(cpu, p->mm) = 0; >> >> Because cpu_context(cpu,mm) will be changed to asid_first_version(cpu) after 'for' loop, >> and in order to improve the efficiency of the loop, I deleted "&& (p->mm != mm)", >> but I forgot to delete the redundant parentheses. > > Note that parens around 'p->mm' were never needed. And neither around the right operand of &&. You are right, I will pay attention to similar problems next time. Thanks for your reminder. Best regards, Jiwei > >> Thanks, >> Best regards, >> Jiwei > > MBR, Sergei >