Date: Tue, 05 Nov 2019 16:04:47 +0109 From: Marc Zyngier <maz@...nel.org> To: Sami Tolvanen <samitolvanen@...gle.com> Cc: Nick Desaulniers <ndesaulniers@...gle.com>, Will Deacon <will@...nel.org>, Catalin Marinas <catalin.marinas@....com>, Steven Rostedt <rostedt@...dmis.org>, Masami Hiramatsu <mhiramat@...nel.org>, Ard Biesheuvel <ard.biesheuvel@...aro.org>, Dave Martin <dave.martin@....com>, Kees Cook <keescook@...omium.org>, Laura Abbott <labbott@...hat.com>, Mark Rutland <mark.rutland@....com>, Jann Horn <jannh@...gle.com>, Miguel Ojeda <miguel.ojeda.sandonis@...il.com>, Masahiro Yamada <yamada.masahiro@...ionext.com>, clang-built-linux <clang-built-linux@...glegroups.com>, Kernel Hardening <kernel-hardening@...ts.openwall.com>, linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>, LKML <linux-kernel@...r.kernel.org> Subject: Re: [PATCH v4 13/17] arm64: preserve x18 when CPU is suspended On 2019-11-05 01:11, Sami Tolvanen wrote: > On Mon, Nov 4, 2019 at 1:59 PM Nick Desaulniers > <ndesaulniers@...gle.com> wrote: >> >> On Mon, Nov 4, 2019 at 1:38 PM Sami Tolvanen >> <samitolvanen@...gle.com> wrote: >> > >> > On Mon, Nov 4, 2019 at 5:20 AM Marc Zyngier <maz@...nel.org> >> wrote: >> > > > ENTRY(cpu_do_suspend) >> > > > mrs x2, tpidr_el0 >> > > > @@ -73,6 +75,9 @@ alternative_endif >> > > > stp x8, x9, [x0, #48] >> > > > stp x10, x11, [x0, #64] >> > > > stp x12, x13, [x0, #80] >> > > > +#ifdef CONFIG_SHADOW_CALL_STACK >> > > > + str x18, [x0, #96] >> > > > +#endif >> > > >> > > Do we need the #ifdefery here? We didn't add that to the KVM >> path, >> > > and I'd feel better having a single behaviour, specially when >> > > NR_CTX_REGS is unconditionally sized to hold 13 regs. >> > >> > I'm fine with dropping the ifdefs here in v5 unless someone >> objects to this. >> >> Oh, yeah I guess it would be good to be consistent. Rather than >> drop >> the ifdefs, would you (Marc) be ok with conditionally setting >> NR_CTX_REGS based on CONFIG_SHADOW_CALL_STACK, and doing so in KVM? >> (So 3 ifdefs, rather than 0)? >> >> Without any conditionals or comments, it's not clear why x18 is >> being >> saved and restored (unless git blame survives, or a comment is added >> in place of the ifdefs in v6). > > True. Clearing the sleep state buffer in cpu_do_resume is also > pointless without CONFIG_SHADOW_CALL_STACK, so if the ifdefs are > removed, some kind of an explanation is needed there. I can't imagine the overhead being noticeable, and I certainly value minimizing the testing space. Sticking a comment there should be enough for people hacking on this to understand that this isn't entirely dead code. Thanks, M. -- Jazz is not dead. It just smells funny...
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