Re: [kvm-unit-tests PATCH 1/6] s390x: Use interrupts in SCLP and add locking

Thomas Huth
2019-09-02T11:42:50Z

On 30/08/2019 14.21, David Hildenbrand wrote:
> On 29.08.19 14:14, Janosch Frank wrote:
>> We need to properly implement interrupt handling for SCLP, because on
>> z/VM and LPAR SCLP calls are not synchronous!
>>
>> Also with smp CPUs have to compete for sclp. Let's add some locking,
>> so they execute sclp calls in an orderly fashion and don't compete for
>> the data buffer.
>>
>> Signed-off-by: Janosch Frank <frankja@linux.ibm.com>
>> ---
>> lib/s390x/asm/interrupt.h | 2 ++
>> lib/s390x/interrupt.c | 12 +++++++--
>> lib/s390x/sclp-console.c | 2 ++
>> lib/s390x/sclp.c | 54 +++++++++++++++++++++++++++++++++++++--
>> lib/s390x/sclp.h | 3 +++
>> 5 files changed, 69 insertions(+), 4 deletions(-)
>>
>> diff --git a/lib/s390x/asm/interrupt.h b/lib/s390x/asm/interrupt.h
>> index 013709f..f485e96 100644
>> --- a/lib/s390x/asm/interrupt.h
>> +++ b/lib/s390x/asm/interrupt.h
>> @@ -11,6 +11,8 @@
>> #define _ASMS390X_IRQ_H_
>> #include <asm/arch_def.h>
>>
>> +#define EXT_IRQ_SERVICE_SIG 0x2401
>> +
>> void handle_pgm_int(void);
>> void handle_ext_int(void);
>> void handle_mcck_int(void);
>> diff --git a/lib/s390x/interrupt.c b/lib/s390x/interrupt.c
>> index cf0a794..7832711 100644
>> --- a/lib/s390x/interrupt.c
>> +++ b/lib/s390x/interrupt.c
>> @@ -12,6 +12,7 @@
>> #include <libcflat.h>
>> #include <asm/interrupt.h>
>> #include <asm/barrier.h>
>> +#include <sclp.h>
>>
>> static bool pgm_int_expected;
>> static struct lowcore *lc;
>> @@ -107,8 +108,15 @@ void handle_pgm_int(void)
>>
>> void handle_ext_int(void)
>> {
>> - report_abort("Unexpected external call interrupt: at %#lx",
>> - lc->ext_old_psw.addr);
>> + if (lc->ext_int_code != EXT_IRQ_SERVICE_SIG) {
>> + report_abort("Unexpected external call interrupt: at %#lx",
>> + lc->ext_old_psw.addr);
>> + } else {
>> + lc->ext_old_psw.mask &= ~PSW_MASK_EXT;
>> + lc->sw_int_cr0 &= ~(1UL << 9);
>> + sclp_handle_ext();
>> + lc->ext_int_code = 0;
>> + }
>> }
>>
>> void handle_mcck_int(void)
>> diff --git a/lib/s390x/sclp-console.c b/lib/s390x/sclp-console.c
>> index bc01f41..a5ef45f 100644
>> --- a/lib/s390x/sclp-console.c
>> +++ b/lib/s390x/sclp-console.c
>> @@ -17,6 +17,7 @@ static void sclp_set_write_mask(void)
>> {
>> WriteEventMask *sccb = (void *)_sccb;
>>
>> + sclp_mark_busy();
>> sccb->h.length = sizeof(WriteEventMask);
>> sccb->mask_length = sizeof(unsigned int);
>> sccb->receive_mask = SCLP_EVENT_MASK_MSG_ASCII;
>> @@ -37,6 +38,7 @@ void sclp_print(const char *str)
>> int len = strlen(str);
>> WriteEventData *sccb = (void *)_sccb;
>>
>> + sclp_mark_busy();
>> sccb->h.length = sizeof(WriteEventData) + len;
>> sccb->h.function_code = SCLP_FC_NORMAL_WRITE;
>> sccb->ebh.length = sizeof(EventBufferHeader) + len;
>> diff --git a/lib/s390x/sclp.c b/lib/s390x/sclp.c
>> index b60f7a4..257eb02 100644
>> --- a/lib/s390x/sclp.c
>> +++ b/lib/s390x/sclp.c
>> @@ -14,6 +14,8 @@
>> #include <asm/page.h>
>> #include <asm/arch_def.h>
>> #include <asm/interrupt.h>
>> +#include <asm/barrier.h>
>> +#include <asm/spinlock.h>
>> #include "sclp.h"
>> #include <alloc_phys.h>
>> #include <alloc_page.h>
>> @@ -25,6 +27,8 @@ static uint64_t max_ram_size;
>> static uint64_t ram_size;
>>
>> char _sccb[PAGE_SIZE] __attribute__((__aligned__(4096)));
>> +static volatile bool sclp_busy;
>> +static struct spinlock sclp_lock;
>>
>> static void mem_init(phys_addr_t mem_end)
>> {
>> @@ -41,17 +45,61 @@ static void mem_init(phys_addr_t mem_end)
>> page_alloc_ops_enable();
>> }
>>
>> +static void sclp_setup_int(void)
>> +{
>> + uint64_t mask;
>> +
>> + ctl_set_bit(0, 9);
>> +
>> + mask = extract_psw_mask();
>> + mask |= PSW_MASK_EXT;
>> + load_psw_mask(mask);
>> +}
>> +
>> +void sclp_handle_ext(void)
>> +{
>> + ctl_clear_bit(0, 9);
>> + spin_lock(&sclp_lock);
>> + sclp_busy = false;
>> + spin_unlock(&sclp_lock);
>> +}
>> +
>> +void sclp_wait_busy(void)
>> +{
>> + while (sclp_busy)
>> + mb();
>> +}
>> +
>> +void sclp_mark_busy(void)
>> +{
>> + /*
>> + * With multiple CPUs we might need to wait for another CPU's
>> + * request before grabbing the busy indication.
>> + */
>> +retry_wait:
>> + sclp_wait_busy();
>> + spin_lock(&sclp_lock);
>> + if (sclp_busy) {
>> + spin_unlock(&sclp_lock);
>> + goto retry_wait;
>> + }
>> + sclp_busy = true;
>> + spin_unlock(&sclp_lock);
>
> while (true) {
> sclp_wait_busy();
> spin_lock(&sclp_lock);
> if (!sclp_busy) {
> sclp_busy = true
> spin_unlock(&sclp_lock);
> break;
> }
> spin_unlock(&sclp_lock);
> }

I'd also prefer this without "goto".

> Or can we simply switch to an atomic_t for sclp_busy and implement
> cmpxchg using __sync_bool_compare_and_swap/ __sync_val_compare_and_swap ?
>
> I guess then we can drop the lock. But maybe I am missing something :)
>
>> +}
>> +
>> static void sclp_read_scp_info(ReadInfo *ri, int length)
>> {
>> unsigned int commands[] = { SCLP_CMDW_READ_SCP_INFO_FORCED,
>> SCLP_CMDW_READ_SCP_INFO };
>> - int i;
>> + int i, cc;
>>
>> for (i = 0; i < ARRAY_SIZE(commands); i++) {
>> + sclp_mark_busy();
>> memset(&ri->h, 0, sizeof(ri->h));
>> ri->h.length = length;
>>
>> - if (sclp_service_call(commands[i], ri))
>> + cc = sclp_service_call(commands[i], ri);
>> + if (cc)
>> break;
>> if (ri->h.response_code == SCLP_RC_NORMAL_READ_COMPLETION)
>> return;
>> @@ -66,12 +114,14 @@ int sclp_service_call(unsigned int command, void *sccb)
>> {
>> int cc;
>>
>> + sclp_setup_int();
>> asm volatile(
>> " .insn rre,0xb2200000,%1,%2\n" /* servc %1,%2 */
>> " ipm %0\n"
>> " srl %0,28"
>> : "=&d" (cc) : "d" (command), "a" (__pa(sccb))
>> : "cc", "memory");
>> + sclp_wait_busy();
>> if (cc == 3)
>> return -1;
>> if (cc == 2)
>> diff --git a/lib/s390x/sclp.h b/lib/s390x/sclp.h
>> index 583c4e5..63cf609 100644
>> --- a/lib/s390x/sclp.h
>> +++ b/lib/s390x/sclp.h
>> @@ -213,6 +213,9 @@ typedef struct ReadEventData {
>> } __attribute__((packed)) ReadEventData;
>>
>> extern char _sccb[];
>> +void sclp_handle_ext(void);
>> +void sclp_wait_busy(void);
>> +void sclp_mark_busy(void);
>
> I wonder if we can find better names ...
>
> sclp_prepare()
> sclp_finalize()
>
> or sth like that.

IMHO "mark_busy" / "wait_busy" is more logical than "prepare" /
"finalize". With "busy" in the name, I can figure out the meaning, while
with "prepare" and "finalize", I'd rather wonder what it is about, I think.

Thomas