Re: [kvm-unit-tests PATCH 4/6] s390x: Add initial smp code

Thomas Huth
2019-09-02T13:21:34Z

On 29/08/2019 14.14, Janosch Frank wrote:
> Let's add a rudimentary SMP library, which will scan for cpus and has
> helper functions that manage the cpu state.
>
> Signed-off-by: Janosch Frank <frankja@linux.ibm.com>
> ---
> lib/s390x/asm/arch_def.h | 8 ++
> lib/s390x/asm/sigp.h | 29 ++++-
> lib/s390x/io.c | 5 +-
> lib/s390x/sclp.h | 1 +
> lib/s390x/smp.c | 272 +++++++++++++++++++++++++++++++++++++++
> lib/s390x/smp.h | 51 ++++++++
> s390x/Makefile | 1 +
> s390x/cstart64.S | 7 +
> 8 files changed, 368 insertions(+), 6 deletions(-)
> create mode 100644 lib/s390x/smp.c
> create mode 100644 lib/s390x/smp.h
>
> diff --git a/lib/s390x/asm/arch_def.h b/lib/s390x/asm/arch_def.h
> index 5f8f45e..d5a7f51 100644
> --- a/lib/s390x/asm/arch_def.h
> +++ b/lib/s390x/asm/arch_def.h
> @@ -157,6 +157,14 @@ struct cpuid {
> uint64_t reserved : 15;
> };
>
> +static inline unsigned short stap(void)
> +{
> + unsigned short cpu_address;
> +
> + asm volatile("stap %0" : "=Q" (cpu_address));
> + return cpu_address;
> +}
> +
> static inline int tprot(unsigned long addr)
> {
> int cc;
> diff --git a/lib/s390x/asm/sigp.h b/lib/s390x/asm/sigp.h
> index fbd94fc..ce85eb7 100644
> --- a/lib/s390x/asm/sigp.h
> +++ b/lib/s390x/asm/sigp.h
> @@ -46,14 +46,33 @@
>
> #ifndef __ASSEMBLER__
>
> -static inline void sigp_stop(void)
> +
> +static inline int sigp(uint16_t addr, uint8_t order, unsigned long parm,
> + uint32_t *status)
> {
> - register unsigned long status asm ("1") = 0;
> - register unsigned long cpu asm ("2") = 0;
> + register unsigned long reg1 asm ("1") = parm;
> + int cc;
>
> asm volatile(
> - " sigp %0,%1,0(%2)\n"
> - : "+d" (status) : "d" (cpu), "d" (SIGP_STOP) : "cc");
> + " sigp %1,%2,0(%3)\n"
> + " ipm %0\n"
> + " srl %0,28\n"
> + : "=d" (cc), "+d" (reg1) : "d" (addr), "a" (order) : "cc");
> + if (status)
> + *status = reg1;
> + return cc;
> +}
> +
> +static inline int sigp_retry(uint16_t addr, uint8_t order, unsigned long parm,
> + uint32_t *status)
> +{
> + int cc;
> +
> +retry:
> + cc = sigp(addr, order, parm, status);
> + if (cc == 2)
> + goto retry;

Please change to:

do {
cc = sigp(addr, order, parm, status);
} while (cc == 2);

> + return cc;
> }
>
> #endif /* __ASSEMBLER__ */
[...]
> diff --git a/lib/s390x/smp.c b/lib/s390x/smp.c
> new file mode 100644
> index 0000000..b1b636a
> --- /dev/null
> +++ b/lib/s390x/smp.c
[...]
> +int smp_cpu_restart(uint16_t addr)
> +{
> + int rc = 0;
> + struct cpu *cpu;
> +
> + spin_lock(&lock);
> + cpu = smp_cpu_from_addr(addr);
> + if (!cpu) {
> + rc = -ENOENT;
> + goto out;
> + }
> +
> + rc = sigp(cpu->addr, SIGP_RESTART, 0, NULL);

I think you could use "addr" instead of "cpu->addr" here.

> + cpu->active = true;
> +out:
> + spin_unlock(&lock);
> + return rc;
> +}
> +
> +int smp_cpu_start(uint16_t addr, struct psw psw)
> +{
> + int rc = 0;
> + struct cpu *cpu;
> + struct lowcore *lc;
> +
> + spin_lock(&lock);
> + cpu = smp_cpu_from_addr(addr);
> + if (!cpu) {
> + rc = -ENOENT;
> + goto out;
> + }
> +
> + lc = cpu->lowcore;
> + lc->restart_new_psw.mask = psw.mask;
> + lc->restart_new_psw.addr = psw.addr;
> + rc = sigp(cpu->addr, SIGP_RESTART, 0, NULL);

dito

> +out:
> + spin_unlock(&lock);
> + return rc;
> +}
> +
> +int smp_cpu_destroy(uint16_t addr)
> +{
> + struct cpu *cpu;
> + int rc = 0;
> +
> + spin_lock(&lock);
> + rc = smp_cpu_stop_nolock(addr, false);
> + if (rc)
> + goto out;
> +
> + cpu = smp_cpu_from_addr(addr);
> + free_pages(cpu->lowcore, 2 * PAGE_SIZE);
> + free_pages(cpu->stack, 4 * PAGE_SIZE);

Maybe do this afterwards to make sure that nobody uses a dangling pointer:

cpu->lowcore = cpu->stack = -1UL;

?

> +out:
> + spin_unlock(&lock);
> + return rc;
> +}
> +
> +int smp_cpu_setup(uint16_t addr, struct psw psw)
> +{
> + struct lowcore *lc;
> + struct cpu *cpu;
> + int rc = 0;
> +
> + spin_lock(&lock);
> +
> + if (!cpus) {
> + rc = -EINVAL;
> + goto out;
> + }
> +
> + cpu = smp_cpu_from_addr(addr);
> +
> + if (!cpu) {
> + rc = -ENOENT;
> + goto out;
> + }
> +
> + if (cpu->active) {
> + rc = -EINVAL;
> + goto out;
> + }
> +
> + sigp_retry(cpu->addr, SIGP_INITIAL_CPU_RESET, 0, NULL);
> +
> + lc = alloc_pages(1);
> + cpu->lowcore = lc;
> + memset(lc, 0, PAGE_SIZE * 2);
> + sigp_retry(cpu->addr, SIGP_SET_PREFIX, (unsigned long )lc, NULL);
> +
> + /* Copy all exception psws. */
> + memcpy(lc, cpu0->lowcore, 512);
> +
> + /* Setup stack */
> + cpu->stack = (uint64_t *)alloc_pages(2);
> +
> + /* Start without DAT and any other mask bits. */
> + cpu->lowcore->sw_int_grs[14] = psw.addr;
> + cpu->lowcore->sw_int_grs[15] = (uint64_t)cpu->stack + (PAGE_SIZE * 4) / sizeof(cpu->stack);

The end-of-stack calculation looks wrong to me. I think you either meant:

... = (uint64_t)(cpu->stack + (PAGE_SIZE * 4) / sizeof(*cpu->stack));

or:

... = (uint64_t)cpu->stack + (PAGE_SIZE * 4);

?

> + lc->restart_new_psw.mask = 0x0000000180000000UL;
> + lc->restart_new_psw.addr = (unsigned long)smp_cpu_setup_state;

Maybe use "(uint64_t)" instead of "(unsigned long)"?

> + lc->sw_int_cr0 = 0x0000000000040000UL;
> +
> + /* Start processing */
> + cpu->active = true;
> + rc = sigp_retry(cpu->addr, SIGP_RESTART, 0, NULL);

Should cpu->active only be set to true if rc == 0 ?

> +out:
> + spin_unlock(&lock);
> + return rc;
> +}
> +
> +/*
> + * Disregarding state, stop all cpus that once were online except for
> + * calling cpu.
> + */
> +void smp_teardown(void)
> +{
> + int i = 0;
> + uint16_t this_cpu = stap();
> + struct ReadCpuInfo *info = (void *)cpu_info_buffer;
> +
> + spin_lock(&lock);
> + for (; i < info->nr_configured; i++) {
> + if (cpus[i].active &&
> + cpus[i].addr != this_cpu) {
> + sigp_retry(cpus[i].addr, SIGP_STOP, 0, NULL);

Maybe set cpus[i].active = false afterwards ?

> + }
> + }
> + spin_unlock(&lock);
> +}

Thomas