[kvm-unit-tests,v4,4/9] s390x: smp: Rework cpu start and active tracking
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Message ID 20200121134254.4570-5-frankja@linux.ibm.com
State New
Headers show
Series
  • s390x: smp: Improve smp code and reset checks
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Commit Message

Janosch Frank Jan. 21, 2020, 1:42 p.m. UTC
The architecture specifies that processing sigp orders may be
asynchronous, and this is indeed the case on some hypervisors, so we
need to wait until the cpu runs before we return from the setup/start
function.

As there was a lot of duplicate code, a common function for cpu
restarts has been introduced.

Signed-off-by: Janosch Frank <frankja@linux.ibm.com>
Reviewed-by: Cornelia Huck <cohuck@redhat.com>
---
 lib/s390x/smp.c | 50 ++++++++++++++++++++++++++++---------------------
 1 file changed, 29 insertions(+), 21 deletions(-)

Comments

David Hildenbrand Jan. 21, 2020, 5:40 p.m. UTC | #1
On 21.01.20 14:42, Janosch Frank wrote:
> The architecture specifies that processing sigp orders may be
> asynchronous, and this is indeed the case on some hypervisors, so we
> need to wait until the cpu runs before we return from the setup/start
> function.
> 
> As there was a lot of duplicate code, a common function for cpu
> restarts has been introduced.
> 
> Signed-off-by: Janosch Frank <frankja@linux.ibm.com>
> Reviewed-by: Cornelia Huck <cohuck@redhat.com>
> ---
>  lib/s390x/smp.c | 50 ++++++++++++++++++++++++++++---------------------
>  1 file changed, 29 insertions(+), 21 deletions(-)
> 
> diff --git a/lib/s390x/smp.c b/lib/s390x/smp.c
> index f57f420..84e681d 100644
> --- a/lib/s390x/smp.c
> +++ b/lib/s390x/smp.c
> @@ -104,35 +104,46 @@ int smp_cpu_stop_store_status(uint16_t addr)
>  	return rc;
>  }
>  
> +static int smp_cpu_restart_nolock(uint16_t addr, struct psw *psw)
> +{
> +	int rc;
> +	struct cpu *cpu = smp_cpu_from_addr(addr);
> +
> +	if (!cpu)
> +		return -1;
> +	if (psw) {
> +		cpu->lowcore->restart_new_psw.mask = psw->mask;
> +		cpu->lowcore->restart_new_psw.addr = psw->addr;
> +	}
> +	rc = sigp(addr, SIGP_RESTART, 0, NULL);
> +	if (rc)
> +		return rc;
> +	/*
> +	 * The order has been accepted, but the actual restart may not
> +	 * have been performed yet, so wait until the cpu is running.
> +	 */
> +	while (!smp_cpu_running(addr))
> +		mb();
> +	cpu->active = true;
> +	return 0;
> +}
> +

Just wondering what happened to my comment

"Should you make sure to stop the CPU before issuing the restart?
Otherwise you will get false positives if it is still running (but
hasn't processed the RESTART yet)"

?

IOW, should we have a SIGP_STOP before issuing the SIGP_RESTART?
Janosch Frank Jan. 22, 2020, 8:25 a.m. UTC | #2
On 1/21/20 6:40 PM, David Hildenbrand wrote:
> On 21.01.20 14:42, Janosch Frank wrote:
>> The architecture specifies that processing sigp orders may be
>> asynchronous, and this is indeed the case on some hypervisors, so we
>> need to wait until the cpu runs before we return from the setup/start
>> function.
>>
>> As there was a lot of duplicate code, a common function for cpu
>> restarts has been introduced.
>>
>> Signed-off-by: Janosch Frank <frankja@linux.ibm.com>
>> Reviewed-by: Cornelia Huck <cohuck@redhat.com>
>> ---
>>  lib/s390x/smp.c | 50 ++++++++++++++++++++++++++++---------------------
>>  1 file changed, 29 insertions(+), 21 deletions(-)
>>
>> diff --git a/lib/s390x/smp.c b/lib/s390x/smp.c
>> index f57f420..84e681d 100644
>> --- a/lib/s390x/smp.c
>> +++ b/lib/s390x/smp.c
>> @@ -104,35 +104,46 @@ int smp_cpu_stop_store_status(uint16_t addr)
>>  	return rc;
>>  }
>>  
>> +static int smp_cpu_restart_nolock(uint16_t addr, struct psw *psw)
>> +{
>> +	int rc;
>> +	struct cpu *cpu = smp_cpu_from_addr(addr);
>> +
>> +	if (!cpu)
>> +		return -1;
>> +	if (psw) {
>> +		cpu->lowcore->restart_new_psw.mask = psw->mask;
>> +		cpu->lowcore->restart_new_psw.addr = psw->addr;
>> +	}
>> +	rc = sigp(addr, SIGP_RESTART, 0, NULL);
>> +	if (rc)
>> +		return rc;
>> +	/*
>> +	 * The order has been accepted, but the actual restart may not
>> +	 * have been performed yet, so wait until the cpu is running.
>> +	 */
>> +	while (!smp_cpu_running(addr))
>> +		mb();
>> +	cpu->active = true;
>> +	return 0;
>> +}
>> +
> 
> Just wondering what happened to my comment

It probably got lost in your other change requests :)

> 
> "Should you make sure to stop the CPU before issuing the restart?
> Otherwise you will get false positives if it is still running (but
> hasn't processed the RESTART yet)"
> 
> ?
> 
> IOW, should we have a SIGP_STOP before issuing the SIGP_RESTART?

Yes, that would be cleaner.

Patch
diff mbox series

diff --git a/lib/s390x/smp.c b/lib/s390x/smp.c
index f57f420..84e681d 100644
--- a/lib/s390x/smp.c
+++ b/lib/s390x/smp.c
@@ -104,35 +104,46 @@  int smp_cpu_stop_store_status(uint16_t addr)
 	return rc;
 }
 
+static int smp_cpu_restart_nolock(uint16_t addr, struct psw *psw)
+{
+	int rc;
+	struct cpu *cpu = smp_cpu_from_addr(addr);
+
+	if (!cpu)
+		return -1;
+	if (psw) {
+		cpu->lowcore->restart_new_psw.mask = psw->mask;
+		cpu->lowcore->restart_new_psw.addr = psw->addr;
+	}
+	rc = sigp(addr, SIGP_RESTART, 0, NULL);
+	if (rc)
+		return rc;
+	/*
+	 * The order has been accepted, but the actual restart may not
+	 * have been performed yet, so wait until the cpu is running.
+	 */
+	while (!smp_cpu_running(addr))
+		mb();
+	cpu->active = true;
+	return 0;
+}
+
 int smp_cpu_restart(uint16_t addr)
 {
-	int rc = -1;
-	struct cpu *cpu;
+	int rc;
 
 	spin_lock(&lock);
-	cpu = smp_cpu_from_addr(addr);
-	if (cpu) {
-		rc = sigp(addr, SIGP_RESTART, 0, NULL);
-		cpu->active = true;
-	}
+	rc = smp_cpu_restart_nolock(addr, NULL);
 	spin_unlock(&lock);
 	return rc;
 }
 
 int smp_cpu_start(uint16_t addr, struct psw psw)
 {
-	int rc = -1;
-	struct cpu *cpu;
-	struct lowcore *lc;
+	int rc;
 
 	spin_lock(&lock);
-	cpu = smp_cpu_from_addr(addr);
-	if (cpu) {
-		lc = cpu->lowcore;
-		lc->restart_new_psw.mask = psw.mask;
-		lc->restart_new_psw.addr = psw.addr;
-		rc = sigp(addr, SIGP_RESTART, 0, NULL);
-	}
+	rc = smp_cpu_restart_nolock(addr, &psw);
 	spin_unlock(&lock);
 	return rc;
 }
@@ -192,10 +203,7 @@  int smp_cpu_setup(uint16_t addr, struct psw psw)
 	lc->sw_int_crs[0] = 0x0000000000040000UL;
 
 	/* Start processing */
-	rc = sigp_retry(cpu->addr, SIGP_RESTART, 0, NULL);
-	if (!rc)
-		cpu->active = true;
-
+	smp_cpu_restart_nolock(addr, NULL);
 out:
 	spin_unlock(&lock);
 	return rc;