Re: [kvm-unit-tests PATCH v2 1/6] s390x: Use interrupts in SCLP and add locking

[David Hildenbrand <david@redhat.com>]

On 10.09.19 12:14, David Hildenbrand wrote:
> On 05.09.19 12:39, 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          | 55 +++++++++++++++++++++++++++++++++++++--
>>  lib/s390x/sclp.h          |  3 +++
>>  5 files changed, 70 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..56fca0c 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 +45,62 @@ 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.
>> +	 */
>> +	while (true) {
>> +		sclp_wait_busy();
>> +		spin_lock(&sclp_lock);
>> +		if (!sclp_busy) {
>> +			sclp_busy = true;
>> +			spin_unlock(&sclp_lock);
>> +			return;
>> +		}
>> +		spin_unlock(&sclp_lock);
>> +	}
>> +}
>> +
>>  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 +115,14 @@ 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);
>>  void sclp_console_setup(void);
>>  void sclp_print(const char *str);
>>  int sclp_service_call(unsigned int command, void *sccb);
>>
> 
> I was wondering whether it would make sense to enable sclp interrupts as
> default for all CPUs (once in a reasonable state after brought up), and
> simply let any CPU process the request. Initially, we could only let the
> boot CPU handle them.
> 
> You already decoupled sclp_mark_busy() and sclp_setup_int() already. The
> part would have to be moved to the CPU init stage and sclp_handle_ext()
> would simply not clear the interrupt-enable flag.
> 
> Opinions?
> 

OTOH, the s390x-ccw bios enables interrupts on the single cpu after
sending the request, and disables them again in the interrupt handler. I
guess we should never get more than one interrupt per SCLP request?

-- 

Thanks,

David / dhildenb