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Subject: Re: [PATCH v4 05/11] iommu/sva: Assign a PASID to mm on PASID
 allocation and free it on mm exit
To:     Dave Hansen <dave.hansen@intel.com>,
        Joerg Roedel <joro@8bytes.org>,
        Fenghua Yu <fenghua.yu@intel.com>,
        jean-philippe <jean-philippe@linaro.org>
Cc:     Ravi V Shankar <ravi.v.shankar@intel.com>,
        Tony Luck <tony.luck@intel.com>,
        Ashok Raj <ashok.raj@intel.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        x86 <x86@kernel.org>,
        linux-kernel <linux-kernel@vger.kernel.org>,
        iommu <iommu@lists.linux-foundation.org>,
        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
        Andy Lutomirski <luto@kernel.org>,
        Josh Poimboeuf <jpoimboe@redhat.com>,
        Thomas Gleixner <tglx@linutronix.de>
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From:   "zhangfei.gao@foxmail.com" <zhangfei.gao@foxmail.com>
Date:   Mon, 11 Apr 2022 22:44:08 +0800
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On 2022/4/11 下午10:36, Dave Hansen wrote:
> On 4/11/22 07:20, zhangfei.gao@foxmail.com wrote:
>>> Is there nothing before this call trace?  Usually there will be at least
>>> some warning text.
>> I added dump_stack() in ioasid_free.
> Hold on a sec, though...
>
> What's the *problem* here?  Did something break or are you just saying
> that something looks weird to _you_?

After this, nginx is not working at all, and hardware reports error.
Suppose the the master use the ioasid for init, but got freed.

hardware reports:
[  152.731869] hisi_sec2 0000:76:00.0: qm_acc_do_task_timeout [error 
status=0x20] found
[  152.739657] hisi_sec2 0000:76:00.0: qm_acc_wb_not_ready_timeout 
[error status=0x40] found
[  152.747877] hisi_sec2 0000:76:00.0: sec_fsm_hbeat_rint [error 
status=0x20] found
[  152.755340] hisi_sec2 0000:76:00.0: Controller resetting...
[  152.762044] hisi_sec2 0000:76:00.0: QM mailbox operation timeout!
[  152.768198] hisi_sec2 0000:76:00.0: Failed to dump sqc!
[  152.773490] hisi_sec2 0000:76:00.0: Failed to drain out data for 
stopping!
[  152.781426] hisi_sec2 0000:76:00.0: QM mailbox is busy to start!
[  152.787468] hisi_sec2 0000:76:00.0: Failed to dump sqc!
[  152.792753] hisi_sec2 0000:76:00.0: Failed to drain out data for 
stopping!
[  152.800685] hisi_sec2 0000:76:00.0: QM mailbox is busy to start!
[  152.806730] hisi_sec2 0000:76:00.0: Failed to dump sqc!
[  152.812017] hisi_sec2 0000:76:00.0: Failed to drain out data for 
stopping!
[  152.819946] hisi_sec2 0000:76:00.0: QM mailbox is busy to start!
[  152.825992] hisi_sec2 0000:76:00.0: Failed to dump sqc!

Thanks

>
> For instance, if we have:
>
> 	nginx: ioasid_alloc()==1
> 	       fork(); // spawn the daemon
> 	       exit();
> 	       ioasid_free(1);
>
> and then a moment later:
>
> 	lynx:  ioasid_alloc()==1
> 	       fork();
> 	       exit();
> 	       ioasid_free(1);
>
> There's no problem.  The original nginx process with ioasid==1 exited.
> The fact that *some* process called nginx is still running doesn't mean
> that it still has a reference to asid==1.
>
> Are you sure the nginx process that allocated the ASID is the same
> process you see in ps?