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

[Janosch Frank <frankja@linux.ibm.com>]

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On 9/10/19 1:24 PM, David Hildenbrand wrote:
> 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?
> 

Didn't old qemu versions do exactly that an we currently catch that in
the kernel?


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