On Mon, Jul 06, 2026 at 01:17:02PM +0200, Janosch Frank wrote:

On 7/6/26 10:52, Steffen Eiden wrote:

quoted

The Start Arm Execution (SAE) instruction is the centerpiece for
executing arm64 (KVM) guests on s390. Its purpose is, similar to SIE, to
enable accelerated execution of arm64 virtual machines. SAE expects the
physical address of a control block as the only argument.

The host is responsible to save & restore
  - GPRs 0-13
  - access register 0-15
  - breaking event register (BEAR)
  - vector/floating point registers
between SAE executions to guarantee host consistency.

GPRs and BEAR are save and restores in the asm functions. The other
register are handled in within C code. Access registers are handled in a
later patch and SVEs will be handled when they are introduced in a
future series. Most arm64 registers are handled by a satellite block
called save_area. Some registers, frequently used by hypervisors, are
placed into the SAE control block itself.

Enlighten asm/kvm_host_types.h for the new header variant. The new
header is chosen instead of asm/kvm_host_s390_types.h if KVM_S390_ARM64
is defined.

[...]

quoted

+	u64	gpr[31];		/* 0x0300  */
+	u64	_03f8;			/* 0x03f8  */
+
+	union {
+		u64	icptd[8];		/* 0x0400 */
+		/* validity-interception reason; icptr 0x01 */
+#define SAE_VIR_UNKNOWN		0x00
+#define SAE_VIR_UNSUPP_FORMAT	0x01
+#define SAE_VIR_MSO_BOUNDS	0x02
+#define SAE_VIR_MSLA		0x03
+#define SAE_VIR_MGPAS		0x04
+#define SAE_VIR_INVAL_SYSREG	0x05
+#define SAE_VIR_HOST_CONTROL	0x06
+#define SAE_VIR_SCA		0x07
+#define SAE_VIR_MSO_ALIGN	0x08
+#define SAE_VIR_HLC		0x09
+#define SAE_VIR_IRPTC		0x0a

Will these ever be used for something?

I'll remove them.