[kvm-unit-tests,v3,04/13] s390x: Switch to z/Arch if needed
diff mbox series

Message ID 20181218092657.46466-5-frankja@linux.ibm.com
State New
Headers show
Series
  • 390x: Add cross hypervisor and disk boot
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Commit Message

Janosch Frank Dec. 18, 2018, 9:26 a.m. UTC
LPAR and z/VM start in esam mode depending on the hardware, so we need
to switch to z/Arch and set 64 bit addressing.

Under Qemu/KVM we already start out with both when being run with the
Qemu --kernel argument or we lack 64 bit when booting from disk
because of the initial psw specifying 31 bit for z/VM and lpar
compatibility.

Signed-off-by: Janosch Frank <frankja@linux.ibm.com>
Reviewed-by: David Hildenbrand <david@redhat.com>
---
 s390x/cstart64.S | 8 ++++++++
 1 file changed, 8 insertions(+)

Comments

David Hildenbrand Dec. 18, 2018, 9:54 a.m. UTC | #1
On 18.12.18 10:26, Janosch Frank wrote:

s/s390x: Switch to z\/Arch if needed/s390x: Switch to z\/Arch/

As you dropped the condition before the switch

> LPAR and z/VM start in esam mode depending on the hardware, so we need
> to switch to z/Arch and set 64 bit addressing.
> 
> Under Qemu/KVM we already start out with both when being run with the
> Qemu --kernel argument or we lack 64 bit when booting from disk
> because of the initial psw specifying 31 bit for z/VM and lpar
> compatibility.
> 
> Signed-off-by: Janosch Frank <frankja@linux.ibm.com>
> Reviewed-by: David Hildenbrand <david@redhat.com>
> ---
>  s390x/cstart64.S | 8 ++++++++
>  1 file changed, 8 insertions(+)
> 
> diff --git a/s390x/cstart64.S b/s390x/cstart64.S
> index d382497..7886f35 100644
> --- a/s390x/cstart64.S
> +++ b/s390x/cstart64.S
> @@ -20,9 +20,17 @@
>   *
>   * For KVM and TCG kernel boot we are in 64 bit z/Arch mode.
>   * When booting from disk the initial short psw is in 31 bit mode.
> + * When running under LPAR or z/VM, we might start in 31 bit and esam mode.
>   */
>  	.globl start
>  start:
> +	/* Switch to z/Architecture mode and 64-bit */
> +	slr     %r0, %r0		# Set cpuid to zero
> +	lhi     %r1, 2			# mode 2 = esame
> +	sigp    %r1, %r0, 0x12		# sigp set arch

Use the new define for set architecture here?

> +	bras	%r13,0f			# Jump over zero area
> +	.fill	16,4,0x0		# Zero area for lmh
> +0:	lmh	%r0,%r15,0(%r13)	# Clear high-order half of gprs
>  	sam64				# Set addressing mode to 64 bit
>  	/* setup stack */
>  	larl	%r15, stackptr
>
Janosch Frank Dec. 18, 2018, 9:55 a.m. UTC | #2
On 18.12.18 10:54, David Hildenbrand wrote:
> On 18.12.18 10:26, Janosch Frank wrote:
> 
> s/s390x: Switch to z\/Arch if needed/s390x: Switch to z\/Arch/
> 
> As you dropped the condition before the switch
> 
>> LPAR and z/VM start in esam mode depending on the hardware, so we need
>> to switch to z/Arch and set 64 bit addressing.
>>
>> Under Qemu/KVM we already start out with both when being run with the
>> Qemu --kernel argument or we lack 64 bit when booting from disk
>> because of the initial psw specifying 31 bit for z/VM and lpar
>> compatibility.
>>
>> Signed-off-by: Janosch Frank <frankja@linux.ibm.com>
>> Reviewed-by: David Hildenbrand <david@redhat.com>
>> ---
>>  s390x/cstart64.S | 8 ++++++++
>>  1 file changed, 8 insertions(+)
>>
>> diff --git a/s390x/cstart64.S b/s390x/cstart64.S
>> index d382497..7886f35 100644
>> --- a/s390x/cstart64.S
>> +++ b/s390x/cstart64.S
>> @@ -20,9 +20,17 @@
>>   *
>>   * For KVM and TCG kernel boot we are in 64 bit z/Arch mode.
>>   * When booting from disk the initial short psw is in 31 bit mode.
>> + * When running under LPAR or z/VM, we might start in 31 bit and esam mode.
>>   */
>>  	.globl start
>>  start:
>> +	/* Switch to z/Architecture mode and 64-bit */
>> +	slr     %r0, %r0		# Set cpuid to zero
>> +	lhi     %r1, 2			# mode 2 = esame
>> +	sigp    %r1, %r0, 0x12		# sigp set arch
> 
> Use the new define for set architecture here?

Will do

> 
>> +	bras	%r13,0f			# Jump over zero area
>> +	.fill	16,4,0x0		# Zero area for lmh
>> +0:	lmh	%r0,%r15,0(%r13)	# Clear high-order half of gprs
>>  	sam64				# Set addressing mode to 64 bit
>>  	/* setup stack */
>>  	larl	%r15, stackptr
>>
> 
>
Thomas Huth Dec. 18, 2018, 10:04 a.m. UTC | #3
On 2018-12-18 10:26, Janosch Frank wrote:
> LPAR and z/VM start in esam mode depending on the hardware, so we need
> to switch to z/Arch and set 64 bit addressing.
> 
> Under Qemu/KVM we already start out with both when being run with the
> Qemu --kernel argument or we lack 64 bit when booting from disk
> because of the initial psw specifying 31 bit for z/VM and lpar
> compatibility.
> 
> Signed-off-by: Janosch Frank <frankja@linux.ibm.com>
> Reviewed-by: David Hildenbrand <david@redhat.com>
> ---
>  s390x/cstart64.S | 8 ++++++++
>  1 file changed, 8 insertions(+)
> 
> diff --git a/s390x/cstart64.S b/s390x/cstart64.S
> index d382497..7886f35 100644
> --- a/s390x/cstart64.S
> +++ b/s390x/cstart64.S
> @@ -20,9 +20,17 @@
>   *
>   * For KVM and TCG kernel boot we are in 64 bit z/Arch mode.
>   * When booting from disk the initial short psw is in 31 bit mode.
> + * When running under LPAR or z/VM, we might start in 31 bit and esam mode.
>   */
>  	.globl start
>  start:
> +	/* Switch to z/Architecture mode and 64-bit */
> +	slr     %r0, %r0		# Set cpuid to zero
> +	lhi     %r1, 2			# mode 2 = esame
> +	sigp    %r1, %r0, 0x12		# sigp set arch
> +	bras	%r13,0f			# Jump over zero area
> +	.fill	16,4,0x0		# Zero area for lmh
> +0:	lmh	%r0,%r15,0(%r13)	# Clear high-order half of gprs

Do we really want to keep the lmh here? ... yes, I know the kernel is
doing this, too, but I really fail to see why we would need it in the
kvm-unit-tests, too... have you tried it also without this clearing?

 Thomas
Janosch Frank Dec. 18, 2018, 11:45 a.m. UTC | #4
On 18.12.18 11:04, Thomas Huth wrote:
> On 2018-12-18 10:26, Janosch Frank wrote:
>> LPAR and z/VM start in esam mode depending on the hardware, so we need
>> to switch to z/Arch and set 64 bit addressing.
>>
>> Under Qemu/KVM we already start out with both when being run with the
>> Qemu --kernel argument or we lack 64 bit when booting from disk
>> because of the initial psw specifying 31 bit for z/VM and lpar
>> compatibility.
>>
>> Signed-off-by: Janosch Frank <frankja@linux.ibm.com>
>> Reviewed-by: David Hildenbrand <david@redhat.com>
>> ---
>>  s390x/cstart64.S | 8 ++++++++
>>  1 file changed, 8 insertions(+)
>>
>> diff --git a/s390x/cstart64.S b/s390x/cstart64.S
>> index d382497..7886f35 100644
>> --- a/s390x/cstart64.S
>> +++ b/s390x/cstart64.S
>> @@ -20,9 +20,17 @@
>>   *
>>   * For KVM and TCG kernel boot we are in 64 bit z/Arch mode.
>>   * When booting from disk the initial short psw is in 31 bit mode.
>> + * When running under LPAR or z/VM, we might start in 31 bit and esam mode.
>>   */
>>  	.globl start
>>  start:
>> +	/* Switch to z/Architecture mode and 64-bit */
>> +	slr     %r0, %r0		# Set cpuid to zero
>> +	lhi     %r1, 2			# mode 2 = esame
>> +	sigp    %r1, %r0, 0x12		# sigp set arch
>> +	bras	%r13,0f			# Jump over zero area
>> +	.fill	16,4,0x0		# Zero area for lmh
>> +0:	lmh	%r0,%r15,0(%r13)	# Clear high-order half of gprs
> 
> Do we really want to keep the lmh here? ... yes, I know the kernel is
> doing this, too, but I really fail to see why we would need it in the
> kvm-unit-tests, too... have you tried it also without this clearing?
> 
>  Thomas
> 

I think I had it without that for a few days.
What's your reasoning against it? We loose more cycles when clearing BSS
under KVM where it's empty anyway. I'd rather expand it to a lm, to
really have a fresh start.
Thomas Huth Dec. 18, 2018, 12:17 p.m. UTC | #5
On 2018-12-18 12:45, Janosch Frank wrote:
> On 18.12.18 11:04, Thomas Huth wrote:
>> On 2018-12-18 10:26, Janosch Frank wrote:
>>> LPAR and z/VM start in esam mode depending on the hardware, so we need
>>> to switch to z/Arch and set 64 bit addressing.
>>>
>>> Under Qemu/KVM we already start out with both when being run with the
>>> Qemu --kernel argument or we lack 64 bit when booting from disk
>>> because of the initial psw specifying 31 bit for z/VM and lpar
>>> compatibility.
>>>
>>> Signed-off-by: Janosch Frank <frankja@linux.ibm.com>
>>> Reviewed-by: David Hildenbrand <david@redhat.com>
>>> ---
>>>  s390x/cstart64.S | 8 ++++++++
>>>  1 file changed, 8 insertions(+)
>>>
>>> diff --git a/s390x/cstart64.S b/s390x/cstart64.S
>>> index d382497..7886f35 100644
>>> --- a/s390x/cstart64.S
>>> +++ b/s390x/cstart64.S
>>> @@ -20,9 +20,17 @@
>>>   *
>>>   * For KVM and TCG kernel boot we are in 64 bit z/Arch mode.
>>>   * When booting from disk the initial short psw is in 31 bit mode.
>>> + * When running under LPAR or z/VM, we might start in 31 bit and esam mode.
>>>   */
>>>  	.globl start
>>>  start:
>>> +	/* Switch to z/Architecture mode and 64-bit */
>>> +	slr     %r0, %r0		# Set cpuid to zero
>>> +	lhi     %r1, 2			# mode 2 = esame
>>> +	sigp    %r1, %r0, 0x12		# sigp set arch
>>> +	bras	%r13,0f			# Jump over zero area
>>> +	.fill	16,4,0x0		# Zero area for lmh
>>> +0:	lmh	%r0,%r15,0(%r13)	# Clear high-order half of gprs
>>
>> Do we really want to keep the lmh here? ... yes, I know the kernel is
>> doing this, too, but I really fail to see why we would need it in the
>> kvm-unit-tests, too... have you tried it also without this clearing?
> 
> I think I had it without that for a few days.
> What's your reasoning against it?

It just looks weird this way. Like we wanted to execute some 32-bit code
in 64-bit mode afterwards, but we don't do that.

> We loose more cycles when clearing BSS
> under KVM where it's empty anyway. I'd rather expand it to a lm, to
> really have a fresh start.

Fine for me, just add a comment like that ("Clear all registers to make
sure that we have a well-defined fresh start" or so).

I think I'd also rather write this as:

	.irp i, 0,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15
	 xgr \i,\i
	.endr

... since that takes a little bit less space.

 Thomas

Patch
diff mbox series

diff --git a/s390x/cstart64.S b/s390x/cstart64.S
index d382497..7886f35 100644
--- a/s390x/cstart64.S
+++ b/s390x/cstart64.S
@@ -20,9 +20,17 @@ 
  *
  * For KVM and TCG kernel boot we are in 64 bit z/Arch mode.
  * When booting from disk the initial short psw is in 31 bit mode.
+ * When running under LPAR or z/VM, we might start in 31 bit and esam mode.
  */
 	.globl start
 start:
+	/* Switch to z/Architecture mode and 64-bit */
+	slr     %r0, %r0		# Set cpuid to zero
+	lhi     %r1, 2			# mode 2 = esame
+	sigp    %r1, %r0, 0x12		# sigp set arch
+	bras	%r13,0f			# Jump over zero area
+	.fill	16,4,0x0		# Zero area for lmh
+0:	lmh	%r0,%r15,0(%r13)	# Clear high-order half of gprs
 	sam64				# Set addressing mode to 64 bit
 	/* setup stack */
 	larl	%r15, stackptr