Date: Mon, 4 Nov 2019 13:44:30 -0800 From: Sami Tolvanen <samitolvanen@...gle.com> To: Mark Rutland <mark.rutland@....com> Cc: 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>, Marc Zyngier <maz@...nel.org>, Nick Desaulniers <ndesaulniers@...gle.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 03/17] arm64: kvm: stop treating register x18 as caller save On Mon, Nov 4, 2019 at 3:51 AM Mark Rutland <mark.rutland@....com> wrote: > > --- a/arch/arm64/kvm/hyp/entry.S > > +++ b/arch/arm64/kvm/hyp/entry.S > > @@ -23,6 +23,7 @@ > > .pushsection .hyp.text, "ax" > > > > Could we please add a note here, e.g. > > /* > * We treat x18 as callee-saved as the host may use it as a platform > * register (e.g. for shadow call stack). > */ > > ... as that will avoid anyone trying to optimize this away in future > after reading the AAPCS. Sure, that's a good idea. > > .macro restore_callee_saved_regs ctxt > > + // We assume \ctxt is not x18-x28 > > Probably worth s/assume/require/ here. Agreed, I'll change this in v5. Sami
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