From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752751AbdCFIHl (ORCPT ); Mon, 6 Mar 2017 03:07:41 -0500 Received: from mail1.windriver.com ([147.11.146.13]:57365 "EHLO mail1.windriver.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752599AbdCFIHc (ORCPT ); Mon, 6 Mar 2017 03:07:32 -0500 From: jsun4 Subject: Re: [PATCH] MIPS: reset all task's asid to 0 after asid_cache(cpu) overflows To: Sergei Shtylyov , , , References: <1488684260-18867-1-git-send-email-jiwei.sun@windriver.com> <6054d364-5095-d13b-ebf8-a7b6bf8b2024@cogentembedded.com> CC: , , Message-ID: <58BD0E0A.9000402@windriver.com> Date: Mon, 6 Mar 2017 15:21:46 +0800 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.6.0 MIME-Version: 1.0 In-Reply-To: <6054d364-5095-d13b-ebf8-a7b6bf8b2024@cogentembedded.com> Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit X-Originating-IP: [128.224.155.85] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hello Sergei, Thanks for your reply. On 03/05/2017 05:38 PM, Sergei Shtylyov wrote: > Hello! > > On 3/5/2017 6:24 AM, Jiwei Sun 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. Thanks, Best regards, Jiwei > >> + cpu_context(cpu, p->mm) = 0; >> + } >> asid = asid_first_version(cpu); >> + } >> } >> >> cpu_context(cpu, mm) = asid_cache(cpu) = asid; > > MBR, Sergei >