[kvm-unit-tests,1/6] s390x: Use interrupts in SCLP and add locking
diff mbox series

Message ID 20190829121459.1708-2-frankja@linux.ibm.com
State New
Headers show
Series
  • s390x: Add multiboot and smp
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Commit Message

Janosch Frank Aug. 29, 2019, 12:14 p.m. UTC
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(-)

Comments

David Hildenbrand Aug. 30, 2019, 12:21 p.m. UTC | #1
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);
}

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.
Thomas Huth Sept. 2, 2019, 11:42 a.m. UTC | #2
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
Janosch Frank Sept. 3, 2019, 7:53 a.m. UTC | #3
On 8/30/19 2:21 PM, 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.

[...]

>> +
>> +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);
> }
> 
> 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 :)

If you want to add it and it works, I'm open for it :)
Until then I'm taking your suggestion.

> 
>> +}
[...]
>>  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.

Hmm, IMHO my names are a bit better, since they clearly state, that we
wait until the other user has finished.
David Hildenbrand Sept. 3, 2019, 8:52 a.m. UTC | #4
On 03.09.19 09:53, Janosch Frank wrote:
> On 8/30/19 2:21 PM, 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.
> 
> [...]
> 
>>> +
>>> +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);
>> }
>>
>> 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 :)
> 
> If you want to add it and it works, I'm open for it :)
> Until then I'm taking your suggestion.
> 
>>
>>> +}
> [...]
>>>  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.
> 
> Hmm, IMHO my names are a bit better, since they clearly state, that we
> wait until the other user has finished.
> 
> 

I don't like "sclp_wait_busy()" as it is not clear from the name that we
are waiting until we can mark it busy :) It is rather a
"sclp_wait_not_busy()" + marking it busy.

I'm not able to come up with a better name right now :)

Patch
diff mbox series

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);
+}
+
 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);
 void sclp_console_setup(void);
 void sclp_print(const char *str);
 int sclp_service_call(unsigned int command, void *sccb);