Re: [kvm-unit-tests PATCH v4 04/13] s390x: Switch to z/Arch

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Hi Janosch,

happy new year!

On 03.01.2019 11:07, Janosch Frank wrote:
LPAR and z/VM start in esam mode depending on the hardware, so we need

Did you consider the CZAM facility? You already use a so called "short PSW" (which is compatible to the ESA/390 PSW, as you did not set bit 31).

LPAR and z/VM start in esam or esame mode, depending on the hardware CZAM facility and z/VM MACHINE setting.

See POP section "Load State":

"When neither the configuration-z/Architecture-architectural-mode (CZAM) facility nor the ESA/390-compatibility-mode facility are installed, this sets the architectural mode to the ESA/390 mode. When the ESA/390-compatibility-mode facility is installed, this sets the architecture mode to the ESA/390-compatibility mode. When the CZAM facility is installed, the architectural mode is unchanged (that is, it remains in the z/Architecture architectural mode)."

to switch to z/Arch and set 64 bit addressing.

Wouldn't it be nice to mention this in the commit subject:

s390x: Switch to z/Arch and 64-bit addressing [mode]

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 | 10 ++++++++++
  1 file changed, 10 insertions(+)

diff --git a/s390x/cstart64.S b/s390x/cstart64.S
index d382497..6622633 100644
--- a/s390x/cstart64.S
+++ b/s390x/cstart64.S
@@ -11,6 +11,7 @@
   * under the terms of the GNU Library General Public License version 2.
   */
  #include <asm/asm-offsets.h>
+#include <asm/sigp.h>
.section .init @@ -20,9 +21,18 @@
   *
   * 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, SIGP_SET_ARCHITECTURE
+	/* XOR all registers with themselves to clear them fully. */
+	.irp i, 0,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15
+	xgr \i,\i
+	.endr
  	sam64				# Set addressing mode to 64 bit
  	/* setup stack */
  	larl	%r15, stackptr


Regards,
Jens
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