From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752796AbdCFIfY (ORCPT ); Mon, 6 Mar 2017 03:35:24 -0500 Received: from mail-lf0-f48.google.com ([209.85.215.48]:35353 "EHLO mail-lf0-f48.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752599AbdCFIfF (ORCPT ); Mon, 6 Mar 2017 03:35:05 -0500 Subject: Re: [PATCH] MIPS: reset all task's asid to 0 after asid_cache(cpu) overflows To: jsun4 , ralf@linux-mips.org, paul.burton@imgtec.com, james.hogan@imgtec.com References: <1488684260-18867-1-git-send-email-jiwei.sun@windriver.com> <6054d364-5095-d13b-ebf8-a7b6bf8b2024@cogentembedded.com> <58BD0E0A.9000402@windriver.com> Cc: linux-mips@linux-mips.org, linux-kernel@vger.kernel.org, jiwei.sun.bj@qq.com From: Sergei Shtylyov Message-ID: <702ff6e3-9bc7-755b-56ec-86394d959230@cogentembedded.com> Date: Mon, 6 Mar 2017 11:34:03 +0300 User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:45.0) Gecko/20100101 Thunderbird/45.7.1 MIME-Version: 1.0 In-Reply-To: <58BD0E0A.9000402@windriver.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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 &&. > Thanks, > Best regards, > Jiwei MBR, Sergei