Re: [Xen-devel] [PATCH v2 3/6] xen/arm: add SMC wrapper that is compatible with SMCCC v1.0

[Julien Grall <julien.grall@xxxxxxx>]

Hi Stefano,

On 09/26/2018 12:50 AM, Stefano Stabellini wrote:
> On Tue, 25 Sep 2018, Julien Grall 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 v1.0.
> >
> > This patch adds a wrapper for both arm32 and arm64. In the case of
> > arm32, the wrapper is just an alias to the ARM SMCCC v1.1 as the
> > convention is the same.
> >
> > CC: "Edgar E. Iglesias" <edgar.iglesias@xxxxxxxxxx>
> > Signed-off-by: Volodymyr Babchuk <volodymyr_babchuk@xxxxxxxx>
> > [julien: Rework the wrapper to make it closer to SMCC 1.1 wrapper]
> > Signed-off-by: Julien Grall <julien.grall@xxxxxxx>
> I have been struggling to find the old doc for SMCCC v1.0, all the
> references have been updated to v1.1 online now. Do you have a link?
Are you sure? All the references are still to v1.0 (DEN 0028B). See [1].

> > diff --git a/xen/arch/arm/arm64/smc.S b/xen/arch/arm/arm64/smc.S
> > new file mode 100644
> > index 0000000000..b0752be57e
> > --- /dev/null
> > +++ b/xen/arch/arm/arm64/smc.S
> > @@ -0,0 +1,32 @@
> > +/*
> > + * 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.
> > + *
> > + * 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/asm_defns.h>
> > +#include <asm/macros.h>
> > +
> > +/*
> > + * void __arm_smccc_1_0_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,
> > + *                          struct arm_smccc_res *res)
> > + */
> > +ENTRY(__arm_smccc_1_0_smc)
> > +        smc     #0
> > +        ldr     x4, [sp]
> > +        cbz     x4, 1f          /* No need to store the result */
> > +        stp     x0, x1, [x4, #SMCCC_RES_a0]
> > +        stp     x2, x3, [x4, #SMCCC_RES_a2]
> > +1:
> > +        ret
> As I mentioned, I couldn't find the doc, but it looks like the Linux
> implementation always copies back the results
> (arch/arm64/kernel/smccc-call.S)? Shouldn't we zero x0-x3 at least?
Could you provide more details on what looks wrong?

The results are copied in the array res using stp instructions. The only 
difference with Linux implementation is we don't handle quirk.
Cheers,

[1] 
https://developer.arm.com/products/architecture/cpu-architecture/a-profile/docs/den0028/latest/smc-calling-convention-system-software-on-arm-platforms
--
Julien Grall

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