Re: [PATCH kvm-unit-tests v3 8/8] arm/arm64: psci: Don't assume method is hvc

[Alexandru Elisei <alexandru.elisei@arm.com>]

Hi Drew,

On 4/29/21 5:41 PM, Andrew Jones wrote:
> The method can be smc in addition to hvc, and it will be when running
> on bare metal. Additionally, we move the invocations to assembly so
> we don't have to rely on compiler assumptions. We also fix the
> prototype of psci_invoke. It should return long, not int, and
> function_id should be an unsigned int, not an unsigned long.

Sorry to harp on this again, but to be honest, it's still not clear to me why the
psci_invoke_{hvc,smc} functions return a long int.

If we only expect the PSCI functions to return error codes, then the PSCI spec
says these are 32-bit signed integers. If we want to support PSCI functions
returning other values, like PSCI_STAT_{RESIDENCY,COUNT}, then the invoke
functions should return an unsigned value.

The only case we're supporting is the error return for the SMC calling convention
(which says that error codes are 32/64bit signed integers). Since the commit
specifically mentions this change, I think some explanation why this width was
chosen would be appropriate. Unless it's painfully obvious and I'm just not seeing
it, which is a possibility.

Other than that, the patch looks good. I'll some tests to make sure everything is
in order.

Thanks,

Alex

>
> Signed-off-by: Andrew Jones <drjones@redhat.com>
> ---
>  arm/cstart.S       | 22 ++++++++++++++++++++++
>  arm/cstart64.S     | 22 ++++++++++++++++++++++
>  arm/selftest.c     | 34 +++++++---------------------------
>  lib/arm/asm/psci.h | 10 ++++++++--
>  lib/arm/psci.c     | 35 +++++++++++++++++++++++++++--------
>  lib/arm/setup.c    |  2 ++
>  6 files changed, 88 insertions(+), 37 deletions(-)
>
> diff --git a/arm/cstart.S b/arm/cstart.S
> index 446966de350d..2401d92cdadc 100644
> --- a/arm/cstart.S
> +++ b/arm/cstart.S
> @@ -95,6 +95,28 @@ start:
>  
>  .text
>  
> +/*
> + * psci_invoke_hvc / psci_invoke_smc
> + *
> + * Inputs:
> + *   r0 -- function_id
> + *   r1 -- arg0
> + *   r2 -- arg1
> + *   r3 -- arg2
> + *
> + * Outputs:
> + *   r0 -- return code
> + */
> +.globl psci_invoke_hvc
> +psci_invoke_hvc:
> +	hvc	#0
> +	mov	pc, lr
> +
> +.globl psci_invoke_smc
> +psci_invoke_smc:
> +	smc	#0
> +	mov	pc, lr
> +
>  enable_vfp:
>  	/* Enable full access to CP10 and CP11: */
>  	mov	r0, #(3 << 22 | 3 << 20)
> diff --git a/arm/cstart64.S b/arm/cstart64.S
> index 42ba3a3ca249..e4ab7d06251e 100644
> --- a/arm/cstart64.S
> +++ b/arm/cstart64.S
> @@ -109,6 +109,28 @@ start:
>  
>  .text
>  
> +/*
> + * psci_invoke_hvc / psci_invoke_smc
> + *
> + * Inputs:
> + *   w0 -- function_id
> + *   x1 -- arg0
> + *   x2 -- arg1
> + *   x3 -- arg2
> + *
> + * Outputs:
> + *   x0 -- return code
> + */
> +.globl psci_invoke_hvc
> +psci_invoke_hvc:
> +	hvc	#0
> +	ret
> +
> +.globl psci_invoke_smc
> +psci_invoke_smc:
> +	smc	#0
> +	ret
> +
>  get_mmu_off:
>  	adrp	x0, auxinfo
>  	ldr	x0, [x0, :lo12:auxinfo + 8]
> diff --git a/arm/selftest.c b/arm/selftest.c
> index 4495b161cdd5..9f459ed3d571 100644
> --- a/arm/selftest.c
> +++ b/arm/selftest.c
> @@ -400,33 +400,13 @@ static void check_vectors(void *arg __unused)
>  	exit(report_summary());
>  }
>  
> -static bool psci_check(void)
> +static void psci_print(void)
>  {
> -	const struct fdt_property *method;
> -	int node, len, ver;
> -
> -	node = fdt_node_offset_by_compatible(dt_fdt(), -1, "arm,psci-0.2");
> -	if (node < 0) {
> -		printf("PSCI v0.2 compatibility required\n");
> -		return false;
> -	}
> -
> -	method = fdt_get_property(dt_fdt(), node, "method", &len);
> -	if (method == NULL) {
> -		printf("bad psci device tree node\n");
> -		return false;
> -	}
> -
> -	if (len < 4 || strcmp(method->data, "hvc") != 0) {
> -		printf("psci method must be hvc\n");
> -		return false;
> -	}
> -
> -	ver = psci_invoke(PSCI_0_2_FN_PSCI_VERSION, 0, 0, 0);
> -	printf("PSCI version %d.%d\n", PSCI_VERSION_MAJOR(ver),
> -				       PSCI_VERSION_MINOR(ver));
> -
> -	return true;
> +	int ver = psci_invoke(PSCI_0_2_FN_PSCI_VERSION, 0, 0, 0);
> +	report_info("PSCI version: %d.%d", PSCI_VERSION_MAJOR(ver),
> +					  PSCI_VERSION_MINOR(ver));
> +	report_info("PSCI method: %s", psci_invoke == psci_invoke_hvc ?
> +				       "hvc" : "smc");
>  }
>  
>  static void cpu_report(void *data __unused)
> @@ -465,7 +445,7 @@ int main(int argc, char **argv)
>  
>  	} else if (strcmp(argv[1], "smp") == 0) {
>  
> -		report(psci_check(), "PSCI version");
> +		psci_print();
>  		on_cpus(cpu_report, NULL);
>  		while (!cpumask_full(&ready))
>  			cpu_relax();
> diff --git a/lib/arm/asm/psci.h b/lib/arm/asm/psci.h
> index 7b956bf5987d..f87fca0422cc 100644
> --- a/lib/arm/asm/psci.h
> +++ b/lib/arm/asm/psci.h
> @@ -3,8 +3,14 @@
>  #include <libcflat.h>
>  #include <linux/psci.h>
>  
> -extern int psci_invoke(unsigned long function_id, unsigned long arg0,
> -		       unsigned long arg1, unsigned long arg2);
> +typedef long (*psci_invoke_fn)(unsigned int function_id, unsigned long arg0,
> +			       unsigned long arg1, unsigned long arg2);
> +extern psci_invoke_fn psci_invoke;
> +extern long psci_invoke_hvc(unsigned int function_id, unsigned long arg0,
> +			    unsigned long arg1, unsigned long arg2);
> +extern long psci_invoke_smc(unsigned int function_id, unsigned long arg0,
> +			    unsigned long arg1, unsigned long arg2);
> +extern void psci_set_conduit(void);
>  extern int psci_cpu_on(unsigned long cpuid, unsigned long entry_point);
>  extern void psci_system_reset(void);
>  extern int cpu_psci_cpu_boot(unsigned int cpu);
> diff --git a/lib/arm/psci.c b/lib/arm/psci.c
> index 936c83948b6a..3053b3041c28 100644
> --- a/lib/arm/psci.c
> +++ b/lib/arm/psci.c
> @@ -6,22 +6,21 @@
>   *
>   * This work is licensed under the terms of the GNU LGPL, version 2.
>   */
> +#include <devicetree.h>
>  #include <asm/psci.h>
>  #include <asm/setup.h>
>  #include <asm/page.h>
>  #include <asm/smp.h>
>  
> -__attribute__((noinline))
> -int psci_invoke(unsigned long function_id, unsigned long arg0,
> -		unsigned long arg1, unsigned long arg2)
> +static long psci_invoke_none(unsigned int function_id, unsigned long arg0,
> +			     unsigned long arg1, unsigned long arg2)
>  {
> -	asm volatile(
> -		"hvc #0"
> -	: "+r" (function_id)
> -	: "r" (arg0), "r" (arg1), "r" (arg2));
> -	return function_id;
> +	printf("No PSCI method configured! Can't invoke...\n");
> +	return PSCI_RET_NOT_PRESENT;
>  }
>  
> +psci_invoke_fn psci_invoke = psci_invoke_none;
> +
>  int psci_cpu_on(unsigned long cpuid, unsigned long entry_point)
>  {
>  #ifdef __arm__
> @@ -56,3 +55,23 @@ void psci_system_off(void)
>  	int err = psci_invoke(PSCI_0_2_FN_SYSTEM_OFF, 0, 0, 0);
>  	printf("CPU%d unable to do system off (error = %d)\n", smp_processor_id(), err);
>  }
> +
> +void psci_set_conduit(void)
> +{
> +	const void *fdt = dt_fdt();
> +	const struct fdt_property *method;
> +	int node, len;
> +
> +	node = fdt_node_offset_by_compatible(fdt, -1, "arm,psci-0.2");
> +	assert_msg(node >= 0, "PSCI v0.2 compatibility required");
> +
> +	method = fdt_get_property(fdt, node, "method", &len);
> +	assert(method != NULL && len == 4);
> +
> +	if (strcmp(method->data, "hvc") == 0)
> +		psci_invoke = psci_invoke_hvc;
> +	else if (strcmp(method->data, "smc") == 0)
> +		psci_invoke = psci_invoke_smc;
> +	else
> +		assert_msg(false, "Unknown PSCI conduit: %s", method->data);
> +}
> diff --git a/lib/arm/setup.c b/lib/arm/setup.c
> index 86f054304baf..bcdf0d78c2e2 100644
> --- a/lib/arm/setup.c
> +++ b/lib/arm/setup.c
> @@ -25,6 +25,7 @@
>  #include <asm/processor.h>
>  #include <asm/smp.h>
>  #include <asm/timer.h>
> +#include <asm/psci.h>
>  
>  #include "io.h"
>  
> @@ -266,6 +267,7 @@ void setup(const void *fdt, phys_addr_t freemem_start)
>  	mem_regions_add_assumed();
>  	mem_init(PAGE_ALIGN((unsigned long)freemem));
>  
> +	psci_set_conduit();
>  	cpu_init();
>  
>  	/* cpu_init must be called before thread_info_init */