Messages in this thread | | | Date | Fri, 22 Jun 2018 16:18:13 -0700 | From | Fenghua Yu <> | Subject | Re: [RFC PATCH 02/16] x86/split_lock: Handle #AC exception for split lock in kernel mode |
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On Fri, Jun 22, 2018 at 01:59:44PM +0200, Thomas Gleixner wrote: > On Fri, 22 Jun 2018, Thomas Gleixner wrote: > > The whole thing is simply: > > > > handle_ac() > > { > > if (user_mode(regs)) { > > do_trap(AC, SIGBUS, ...); > > } else { > > disable_ac_on_local_cpu(); > > WARN_ONCE(1); > > } > > } > > > > That wants #AC enabled as early as possible so the kernel gets as much > > coverage as it can. If it trips in the kernel it's a bug and needs to be > > fixed and we can them fix ONE by ONE. > > That said, #AC is just yet another badly defined and hastily bolted on > (mis)feature. This should have been: > > Bit A: Enable #AC if CPL < 3 > Bit B: Enable #AC if CPL == 3 > > But that would have been too useful and would allow sensible use of #AC > without creating software trainwrecks. >
The two bits would be ideal.
So I will do SIGBUG for user and WARN/disable for kernel in the next version.
Thanks.
-Fenghua
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