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Date: Wed, 11 May 2022 12:23:57 +0000 From: "Hawkins, Nick" <nick.hawkins@....com> To: Will Deacon <will@...nel.org>, Arnd Bergmann <arnd@...db.de> CC: "Verdun, Jean-Marie" <verdun@....com>, Russell King - ARM Linux <linux@...linux.org.uk>, Mark Rutland <mark.rutland@....com>, Linux ARM <linux-arm-kernel@...ts.infradead.org>, Linux Kernel Mailing List <linux-kernel@...r.kernel.org>, Joel Stanley <joel@....id.au> Subject: RE: [PATCH v1] ARM: A9: Add ARM ERRATA 764319 workaround On Tue, May 10, 2022 at 03:01:26PM +0200, Arnd Bergmann wrote: > > On Tue, May 10, 2022 at 1:53 PM Verdun, Jean-Marie <verdun@....com> wrote: > > > > > > Hi Arnd, > > > > > > > Hi Nick, > > > > > > > This seems a bit more complex than necessary. Can't you just use a custom > > > > inline asm with an ex_table entry to catch the fault? Have a look at > > > > __get_user_asm() for an example. > > > > > > > > Arnd > > > > > > We got inspired from debug_reg_hook within the same source file ( > > >./arch/arm/kernel/hw_breakpoint.c ). We chose that path to keep > > >coherency within the source code. We can implement the same fix by > > >using an ex_table entry, but this will create two different ways at > > >catching unknown instruction within the same source file. Will that be ok ? > > > > I got a little lost trying to find where the breakpoint instruction > > comes from that gets trapped here, but I would guess that they had to > > do this using an undef_hook because the ex_table approach does not > > work there for some reason. > > > > I would still pick the ex_table method here if that works. > IIRC, the ex_table handlers are called only for data aborts and are intended to be used to handle cases where we take a fault on a memory access (e.g. translation fault). In this case, we're taking an undefined instruction exception on a cp14 access and so the undef_hook is the right thing to use. Hello Arnd, Given Will's input would you like me to still use the ex_table method? Thanks, -Nick Hawkins
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