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Message-ID: <CABCJKudSBjOkPFZ-DBFRNqQ=kx5u1Q8W6MY0VGoo=5BTakP2dg@mail.gmail.com>
Date: Tue, 22 Oct 2019 14:45:45 -0700
From: Sami Tolvanen <samitolvanen@...gle.com>
To: Marc Zyngier <maz@...nel.org>
Cc: Will Deacon <will@...nel.org>, Catalin Marinas <catalin.marinas@....com>,
Steven Rostedt <rostedt@...dmis.org>, Ard Biesheuvel <ard.biesheuvel@...aro.org>,
Mark Rutland <mark.rutland@....com>, Kees Cook <keescook@...omium.org>,
Kernel Hardening <kernel-hardening@...ts.openwall.com>,
Nick Desaulniers <ndesaulniers@...gle.com>, LKML <linux-kernel@...r.kernel.org>,
clang-built-linux <clang-built-linux@...glegroups.com>, Laura Abbott <labbott@...hat.com>,
Dave Martin <Dave.Martin@....com>,
linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH 03/18] arm64: kvm: stop treating register x18 as caller save
On Tue, Oct 22, 2019 at 10:22 AM Marc Zyngier <maz@...nel.org> wrote:
> > .macro save_callee_saved_regs ctxt
> > + str x18, [\ctxt, #CPU_XREG_OFFSET(18)]
> > stp x19, x20, [\ctxt, #CPU_XREG_OFFSET(19)]
> > stp x21, x22, [\ctxt, #CPU_XREG_OFFSET(21)]
> > stp x23, x24, [\ctxt, #CPU_XREG_OFFSET(23)]
> > @@ -38,6 +39,7 @@
> > ldp x25, x26, [\ctxt, #CPU_XREG_OFFSET(25)]
> > ldp x27, x28, [\ctxt, #CPU_XREG_OFFSET(27)]
> > ldp x29, lr, [\ctxt, #CPU_XREG_OFFSET(29)]
> > + ldr x18, [\ctxt, #CPU_XREG_OFFSET(18)]
>
> There is now an assumption that ctxt is x18 (otherwise why would it be
> out of order?). Please add a comment to that effect.
> > - // Restore guest regs x19-x29, lr
> > + // Restore guest regs x18-x29, lr
> > restore_callee_saved_regs x18
>
> Or you could elect another register such as x29 as the base, and keep
> the above in a reasonable order.
I'm fine with either option. Ard, any thoughts?
Sami
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