Re: [Xen-devel] [RFC PATCH 16/31] arm: add SMC wrapper that is compatible with SMCCC

[Volodymyr Babchuk <volodymyr_babchuk@xxxxxxxx>]

Hi Stefano,

On Mon, Dec 04, 2017 at 06:30:13PM -0800, Stefano Stabellini wrote:
> On Thu, 9 Nov 2017, Oleksandr Tyshchenko wrote:
> > From: Volodymyr Babchuk <volodymyr_babchuk@xxxxxxxx>
> > 
> > Existing SMC wrapper call_smc() allows only 4 parameters and
> > returns only one value. This is enough for existing
> > use in PSCI code, but TEE mediator will need a call that is
> > fully compatible with ARM SMCCC.
> > This patch adds this call for both arm32 and arm64.
> > 
> > There was similar patch by Edgar E. Iglesias ([1]), but looks
> > like it is abandoned.
> > 
> > [1] 
> > https://lists.xenproject.org/archives/html/xen-devel/2017-02/msg00636.html
> > 
> > CC: "Edgar E. Iglesias" <edgar.iglesias@xxxxxxxxxx>
> > 
> > Signed-off-by: Volodymyr Babchuk <volodymyr_babchuk@xxxxxxxx>
> > CC: Stefano Stabellini <sstabellini@xxxxxxxxxx>
> > CC: Julien Grall <julien.grall@xxxxxxxxxx>
> > ---
> >  xen/arch/arm/arm32/Makefile     |  1 +
> >  xen/arch/arm/arm32/smc.S        | 32 ++++++++++++++++++++++++++++++++
> >  xen/arch/arm/arm64/Makefile     |  1 +
> >  xen/arch/arm/arm64/smc.S        | 29 +++++++++++++++++++++++++++++
> >  xen/include/asm-arm/processor.h |  4 ++++
> >  5 files changed, 67 insertions(+)
> >  create mode 100644 xen/arch/arm/arm32/smc.S
> >  create mode 100644 xen/arch/arm/arm64/smc.S
> > 
> > diff --git a/xen/arch/arm/arm32/Makefile b/xen/arch/arm/arm32/Makefile
> > index 0ac254f..a2362f3 100644
> > --- a/xen/arch/arm/arm32/Makefile
> > +++ b/xen/arch/arm/arm32/Makefile
> > @@ -8,6 +8,7 @@ obj-y += insn.o
> >  obj-$(CONFIG_LIVEPATCH) += livepatch.o
> >  obj-y += proc-v7.o proc-caxx.o
> >  obj-y += smpboot.o
> > +obj-y += smc.o
> >  obj-y += traps.o
> >  obj-y += vfp.o
> >  
> > diff --git a/xen/arch/arm/arm32/smc.S b/xen/arch/arm/arm32/smc.S
> > new file mode 100644
> > index 0000000..1cc9528
> > --- /dev/null
> > +++ b/xen/arch/arm/arm32/smc.S
> > @@ -0,0 +1,32 @@
> > +/*
> > + * xen/arch/arm/arm32/smc.S
> > + *
> > + * Wrapper for Secure Monitors Calls
> > + *
> > + * This program is free software; you can redistribute it and/or modify
> > + * it under the terms of the GNU General Public License as published by
> > + * the Free Software Foundation; either version 2 of the License, or
> > + * (at your option) any later version.
> > + *
> > + * This program is distributed in the hope that it will be useful,
> > + * but WITHOUT ANY WARRANTY; without even the implied warranty of
> > + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
> > + * GNU General Public License for more details.
> > + */
> > +
> > +#include <asm/macros.h>
> > +
> > +/*
> > + * void call_smccc_smc(register_t a0, register_t a1, register_t a2,
> > + *                     register_t a3, register_t a4, register_t a5,
> > + *                     register_t a6, register_t a7, register_t res[4])
> > + */
> > +ENTRY(call_smccc_smc)
> > +        mov     r12, sp
> > +        push    {r4-r7}
> > +        ldm     r12, {r4-r7}
> > +        smc     #0
> > +        pop     {r4-r7}
> > +        ldr     r12, [sp, #(4 * 4)]
> 
> I haven't run this, but shouldn't it be:
> 
>   ldr     r12, [sp, #20]
> 
> ?
> 
I took this code from linux (arch/arm/kernel/arm-smccc.h).
But, why #20? There are 5 parameters on the stack: a4-a7 and res:
a4:  [sp]
a5:  [sp, #4]
a6:  [sp, #8]
a7:  [sp, #12]
res: [sp, #16]

We need to save returnred values to res. So it looks right. Unless
I'm terribly wrong :)

> > +        stm     r12, {r0-r3}
> > +        bx      lr
> > diff --git a/xen/arch/arm/arm64/Makefile b/xen/arch/arm/arm64/Makefile
> > index 149b6b3..7831dc1 100644
> > --- a/xen/arch/arm/arm64/Makefile
> > +++ b/xen/arch/arm/arm64/Makefile
> > @@ -8,5 +8,6 @@ obj-y += entry.o
> >  obj-y += insn.o
> >  obj-$(CONFIG_LIVEPATCH) += livepatch.o
> >  obj-y += smpboot.o
> > +obj-y += smc.o
> >  obj-y += traps.o
> >  obj-y += vfp.o
> > diff --git a/xen/arch/arm/arm64/smc.S b/xen/arch/arm/arm64/smc.S
> > new file mode 100644
> > index 0000000..aa44fba
> > --- /dev/null
> > +++ b/xen/arch/arm/arm64/smc.S
> > @@ -0,0 +1,29 @@
> > +/*
> > + * xen/arch/arm/arm64/smc.S
> > + *
> > + * Wrapper for Secure Monitors Calls
> > + *
> > + * This program is free software; you can redistribute it and/or modify
> > + * it under the terms of the GNU General Public License as published by
> > + * the Free Software Foundation; either version 2 of the License, or
> > + * (at your option) any later version.
> > + *
> > + * This program is distributed in the hope that it will be useful,
> > + * but WITHOUT ANY WARRANTY; without even the implied warranty of
> > + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
> > + * GNU General Public License for more details.
> > + */
> > +
> > +#include <asm/macros.h>
> > +
> > +/*
> > + * void call_smccc_smc(register_t a0, register_t a1, register_t a2,
> > + *                     register_t a3, register_t a4, register_t a5,
> > + *                     register_t a6, register_t a7, register_t res[4])
> > + */
> > +ENTRY(call_smccc_smc)
> > +        smc     #0
> > +        ldr     x4, [sp]
> > +        stp     x0, x1, [x4, 0]
> > +        stp     x2, x3, [x4, 16]
> > +        ret
> > diff --git a/xen/include/asm-arm/processor.h 
> > b/xen/include/asm-arm/processor.h
> > index 9f7a42f..4ce5bb6 100644
> > --- a/xen/include/asm-arm/processor.h
> > +++ b/xen/include/asm-arm/processor.h
> > @@ -786,6 +786,10 @@ void vcpu_regs_user_to_hyp(struct vcpu *vcpu,
> >  int call_smc(register_t function_id, register_t arg0, register_t arg1,
> >               register_t arg2);
> >  
> > +void call_smccc_smc(register_t a0, register_t a1, register_t a2,
> > +                    register_t a3, register_t a4, register_t a5,
> > +                    register_t a6, register_t a7, register_t res[4]);
> > +
> >  void do_trap_hyp_serror(struct cpu_user_regs *regs);
> >  
> >  void do_trap_guest_serror(struct cpu_user_regs *regs);
> > -- 
> > 2.7.4
> > 

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