From: Sean Christopherson <sean.j.christopherson@intel.com>
To: Dave Hansen <dave.hansen@linux.intel.com>, linux-kernel@vger.kernel.org
Cc: peterz@infradead.org, tglx@linutronix.de, x86@kernel.org,
luto@kernel.org
Subject: Re: [RFC][PATCH 5/8] x86/mm: fix exception table comments
Date: Mon, 10 Sep 2018 13:43:17 -0700 [thread overview]
Message-ID: <1536612197.3236.13.camel@intel.com> (raw)
In-Reply-To: <bc50acea-ebc9-5be8-0fcc-9b96031a7348@linux.intel.com>
On Fri, 2018-09-07 at 14:51 -0700, Dave Hansen wrote:
> >
> > >
> > > + * 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.
For me, mentioning hw_error_code just muddies the waters, e.g. why is
hw_error_code mentioned when it's not checked in the code? Comments
alone won't help someone that's reading this code and doesn't understand
that hardware sets X86_PF_USER for user-mode accesses. Maybe this?
* 2. The access was an explicit kernel-mode access. X86_PF_USER
* is set in sw_error_code for both user-mode accesses and
* implicit kernel-mode accesses that originated in user mode.
next prev parent reply other threads:[~2018-09-10 20:43 UTC|newest]
Thread overview: 25+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-09-07 19:48 [RFC][PATCH 0/8] x86/mm: page fault handling cleanups Dave Hansen
2018-09-07 19:48 ` [RFC][PATCH 1/8] x86/mm: clarify hardware vs. software "error_code" Dave Hansen
2018-09-07 22:48 ` Andy Lutomirski
2018-09-10 20:07 ` Dave Hansen
2018-09-10 21:17 ` Andy Lutomirski
2018-09-07 19:48 ` [RFC][PATCH 2/8] x86/mm: break out kernel address space handling Dave Hansen
2018-09-07 21:06 ` Sean Christopherson
2018-09-07 21:51 ` Dave Hansen
2018-09-07 22:21 ` Andy Lutomirski
2018-09-07 22:37 ` Dave Hansen
2018-09-07 19:48 ` [RFC][PATCH 3/8] x86/mm: break out user " Dave Hansen
2018-09-08 9:38 ` Peter Zijlstra
2018-09-10 20:20 ` Dave Hansen
2018-09-07 19:48 ` [RFC][PATCH 4/8] x86/mm: add clarifying comments for user addr space Dave Hansen
2018-09-07 19:49 ` [RFC][PATCH 5/8] x86/mm: fix exception table comments Dave Hansen
2018-09-07 21:04 ` Sean Christopherson
2018-09-07 21:51 ` Dave Hansen
2018-09-10 20:43 ` Sean Christopherson [this message]
2018-09-08 0:37 ` Jann Horn
2018-09-07 19:49 ` [RFC][PATCH 6/8] x86/mm: add vsyscall address helper Dave Hansen
2018-09-08 0:46 ` Jann Horn
2018-09-07 19:49 ` [RFC][PATCH 7/8] x86/mm/vsyscall: consider vsyscall page part of user address space Dave Hansen
2018-09-07 22:58 ` Andy Lutomirski
2018-09-08 1:16 ` Jann Horn
2018-09-07 19:49 ` [RFC][PATCH 8/8] x86/mm: remove spurious fault pkey check Dave Hansen
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