Re: [PATCH v5 1/9] xen/arm: smccc: add support for SMCCCv1.2 extended input/output registers

[Bertrand Marquis <Bertrand.Marquis@xxxxxxx>]

Hi Jens,

> On 18 Aug 2022, at 11:55, Jens Wiklander <jens.wiklander@xxxxxxxxxx> wrote:
> 
> SMCCC v1.2 [1] AArch64 allows x0-x17 to be used as both parameter
> registers and result registers for the SMC and HVC instructions.
> 
> Arm Firmware Framework for Armv8-A specification makes use of x0-x7 as
> parameter and result registers.
> 
> Let us add new interface to support this extended set of input/output
> registers.
> 
> This is based on 3fdc0cb59d97 ("arm64: smccc: Add support for SMCCCv1.2
> extended input/output registers") by Sudeep Holla from the Linux kernel
> 
> The SMCCC version reported to the VM is bumped to 1.2 in order to support
> handling FF-A messages.

With this patch, you add something so that you could call SMCCCv1.2 but in 
practice you are not using it anywhere.
I do not think this patch should bump the version we present to guests.

> 
> [1] https://developer.arm.com/documentation/den0028/c/?lang=en
> 
> Reviewed-by: Luca Fancellu <luca.fancellu@xxxxxxx>
> Signed-off-by: Jens Wiklander <jens.wiklander@xxxxxxxxxx>
> ---
> xen/arch/arm/arm64/asm-offsets.c |  9 +++++++
> xen/arch/arm/arm64/smc.S         | 43 ++++++++++++++++++++++++++++++++
> xen/arch/arm/include/asm/smccc.h | 40 +++++++++++++++++++++++++++++
> xen/arch/arm/vsmc.c              |  2 +-
> 4 files changed, 93 insertions(+), 1 deletion(-)
> 
> diff --git a/xen/arch/arm/arm64/asm-offsets.c 
> b/xen/arch/arm/arm64/asm-offsets.c
> index 280ddb55bfd4..1721e1ed26e1 100644
> --- a/xen/arch/arm/arm64/asm-offsets.c
> +++ b/xen/arch/arm/arm64/asm-offsets.c
> @@ -56,6 +56,15 @@ void __dummy__(void)
>    BLANK();
>    OFFSET(SMCCC_RES_a0, struct arm_smccc_res, a0);
>    OFFSET(SMCCC_RES_a2, struct arm_smccc_res, a2);
> +   OFFSET(ARM_SMCCC_1_2_REGS_X0_OFFS, struct arm_smccc_1_2_regs, a0);
> +   OFFSET(ARM_SMCCC_1_2_REGS_X2_OFFS, struct arm_smccc_1_2_regs, a2);
> +   OFFSET(ARM_SMCCC_1_2_REGS_X4_OFFS, struct arm_smccc_1_2_regs, a4);
> +   OFFSET(ARM_SMCCC_1_2_REGS_X6_OFFS, struct arm_smccc_1_2_regs, a6);
> +   OFFSET(ARM_SMCCC_1_2_REGS_X8_OFFS, struct arm_smccc_1_2_regs, a8);
> +   OFFSET(ARM_SMCCC_1_2_REGS_X10_OFFS, struct arm_smccc_1_2_regs, a10);
> +   OFFSET(ARM_SMCCC_1_2_REGS_X12_OFFS, struct arm_smccc_1_2_regs, a12);
> +   OFFSET(ARM_SMCCC_1_2_REGS_X14_OFFS, struct arm_smccc_1_2_regs, a14);
> +   OFFSET(ARM_SMCCC_1_2_REGS_X16_OFFS, struct arm_smccc_1_2_regs, a16);
> }
> 
> /*
> diff --git a/xen/arch/arm/arm64/smc.S b/xen/arch/arm/arm64/smc.S
> index 91bae62dd4d2..c546192e7f2d 100644
> --- a/xen/arch/arm/arm64/smc.S
> +++ b/xen/arch/arm/arm64/smc.S
> @@ -27,3 +27,46 @@ ENTRY(__arm_smccc_1_0_smc)
>         stp     x2, x3, [x4, #SMCCC_RES_a2]
> 1:
>         ret
> +
> +

Please only add one line only here

> +/*
> + * void arm_smccc_1_2_smc(const struct arm_smccc_1_2_regs *args,
> + *                        struct arm_smccc_1_2_regs *res)
> + */
> +ENTRY(arm_smccc_1_2_smc)
> +    /* Save `res` and free a GPR that won't be clobbered */

The comment here should be fixed, you are clobbering x19 hence you need to save 
it.

> +    stp     x1, x19, [sp, #-16]!
> +
> +    /* Ensure `args` won't be clobbered while loading regs in next step */
> +    mov      x19, x0

You do not need to save args (and no code is restoring it).

> +
> +    /* Load the registers x0 - x17 from the struct arm_smccc_1_2_regs */
> +    ldp      x0, x1, [x19, #ARM_SMCCC_1_2_REGS_X0_OFFS]
> +    ldp      x2, x3, [x19, #ARM_SMCCC_1_2_REGS_X2_OFFS]
> +    ldp      x4, x5, [x19, #ARM_SMCCC_1_2_REGS_X4_OFFS]
> +    ldp      x6, x7, [x19, #ARM_SMCCC_1_2_REGS_X6_OFFS]
> +    ldp      x8, x9, [x19, #ARM_SMCCC_1_2_REGS_X8_OFFS]
> +    ldp      x10, x11, [x19, #ARM_SMCCC_1_2_REGS_X10_OFFS]
> +    ldp      x12, x13, [x19, #ARM_SMCCC_1_2_REGS_X12_OFFS]
> +    ldp      x14, x15, [x19, #ARM_SMCCC_1_2_REGS_X14_OFFS]
> +    ldp      x16, x17, [x19, #ARM_SMCCC_1_2_REGS_X16_OFFS]
> +
> +    smc #0
> +
> +    /* Load the `res` from the stack */
> +    ldr      x19, [sp]
> +
> +    /* Store the registers x0 - x17 into the result structure */
> +    stp      x0, x1, [x19, #ARM_SMCCC_1_2_REGS_X0_OFFS]
> +    stp      x2, x3, [x19, #ARM_SMCCC_1_2_REGS_X2_OFFS]
> +    stp      x4, x5, [x19, #ARM_SMCCC_1_2_REGS_X4_OFFS]
> +    stp      x6, x7, [x19, #ARM_SMCCC_1_2_REGS_X6_OFFS]
> +    stp      x8, x9, [x19, #ARM_SMCCC_1_2_REGS_X8_OFFS]
> +    stp      x10, x11, [x19, #ARM_SMCCC_1_2_REGS_X10_OFFS]
> +    stp      x12, x13, [x19, #ARM_SMCCC_1_2_REGS_X12_OFFS]
> +    stp      x14, x15, [x19, #ARM_SMCCC_1_2_REGS_X14_OFFS]
> +    stp      x16, x17, [x19, #ARM_SMCCC_1_2_REGS_X16_OFFS]
> +
> +    /* Restore original x19 */
> +    ldp     xzr, x19, [sp], #16

You should use ldr and just load x19 value here. 

> +    ret
> diff --git a/xen/arch/arm/include/asm/smccc.h 
> b/xen/arch/arm/include/asm/smccc.h
> index b3dbeecc90ad..b5e3f67eb34e 100644
> --- a/xen/arch/arm/include/asm/smccc.h
> +++ b/xen/arch/arm/include/asm/smccc.h
> @@ -33,6 +33,7 @@
> 
> #define ARM_SMCCC_VERSION_1_0   SMCCC_VERSION(1, 0)
> #define ARM_SMCCC_VERSION_1_1   SMCCC_VERSION(1, 1)
> +#define ARM_SMCCC_VERSION_1_2   SMCCC_VERSION(1, 2)
> 
> /*
>  * This file provides common defines for ARM SMC Calling Convention as
> @@ -265,6 +266,45 @@ void __arm_smccc_1_0_smc(register_t a0, register_t a1, 
> register_t a2,
>         else                                                    \
>             arm_smccc_1_0_smc(__VA_ARGS__);                     \
>     } while ( 0 )
> +
> +/**
> + * struct arm_smccc_1_2_regs - Arguments for or Results from SMC call
> + * @a0-a17 argument values from registers 0 to 17
> + */
> +struct arm_smccc_1_2_regs {
> +    unsigned long a0;
> +    unsigned long a1;
> +    unsigned long a2;
> +    unsigned long a3;
> +    unsigned long a4;
> +    unsigned long a5;
> +    unsigned long a6;
> +    unsigned long a7;
> +    unsigned long a8;
> +    unsigned long a9;
> +    unsigned long a10;
> +    unsigned long a11;
> +    unsigned long a12;
> +    unsigned long a13;
> +    unsigned long a14;
> +    unsigned long a15;
> +    unsigned long a16;
> +    unsigned long a17;
> +};
> +
> +/**
> + * arm_smccc_1_2_smc() - make SMC calls
> + * @args: arguments passed via struct arm_smccc_1_2_regs
> + * @res: result values via struct arm_smccc_1_2_regs
> + *
> + * This function is used to make SMC calls following SMC Calling Convention
> + * v1.2 or above. The content of the supplied param are copied from the
> + * structure to registers prior to the SMC instruction. The return values
> + * are updated with the content from registers on return from the SMC
> + * instruction.
> + */
> +void arm_smccc_1_2_smc(const struct arm_smccc_1_2_regs *args,
> +                       struct arm_smccc_1_2_regs *res);
> #endif /* CONFIG_ARM_64 */
> 
> #endif /* __ASSEMBLY__ */
> diff --git a/xen/arch/arm/vsmc.c b/xen/arch/arm/vsmc.c
> index 676740ef1520..6f90c08a6304 100644
> --- a/xen/arch/arm/vsmc.c
> +++ b/xen/arch/arm/vsmc.c
> @@ -93,7 +93,7 @@ static bool handle_arch(struct cpu_user_regs *regs)
>     switch ( fid )
>     {
>     case ARM_SMCCC_VERSION_FID:
> -        set_user_reg(regs, 0, ARM_SMCCC_VERSION_1_1);
> +        set_user_reg(regs, 0, ARM_SMCCC_VERSION_1_2);

As said for the commit message, I do not see what changes are making Xen 
providing 1.2 interface at this stage.

Regards
Bertrand

>         return true;
> 
>     case ARM_SMCCC_ARCH_FEATURES_FID:
> -- 
> 2.31.1
>