Re: [kvm-unit-tests PATCH v3 04/13] s390x: Switch to z/Arch if needed

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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@xxxxxxxxxxxxx>
> Reviewed-by: David Hildenbrand <david@xxxxxxxxxx>
> ---
>  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




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