linux-kernel - Re: [RFC][PATCH 5/8] x86/mm: fix exception table comments

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Date:   Fri, 7 Sep 2018 14:51:02 -0700
From:   Dave Hansen <dave.hansen@...ux.intel.com>
To:     Sean Christopherson <sean.j.christopherson@...el.com>,
        linux-kernel@...r.kernel.org
Cc:     peterz@...radead.org, tglx@...utronix.de, x86@...nel.org,
        luto@...nel.org
Subject: Re: [RFC][PATCH 5/8] x86/mm: fix exception table comments


>> +	 * Only do the expensive exception table search when we might be at
>> +	 * risk of a deadlock:
>> +	 * 1. We failed to acquire mmap_sem, and
>> +	 * 2. The access was an explicit kernel-mode access
>> +	 *    (X86_PF_USER=0).
> 
> Might be worth reminding the reader that X86_PF_USER will be set in
> sw_error_code for implicit accesses.  I saw "explicit" and my mind
> immediately jumped to hw_error_code for whatever reason.  E.g.:
> 
> 	* 2. The access was an explicit kernel-mode access (we set X86_PF_USER
> 	*    in sw_error_code for implicit kernel-mode accesses).

Yeah, that was not worded well.  Is this better?

>          * Only do the expensive exception table search when we might be at
>          * risk of a deadlock:
>          * 1. We failed to acquire mmap_sem, and
>          * 2. The access was an explicit kernel-mode access.  An access
>          *    from user-mode will X86_PF_USER=1 set via hw_error_code or
>          *    set in sw_error_code if it were an implicit kernel-mode
>          *    access that originated in user mode.