KVM: s390: improve documentation for S390_MEM_OP

flag KVM_S390_MEMOP_F_INJECT_EXCEPTION is set in the "flags" field.

The start address of the memory region has to be specified in the "gaddr"

field, and the length of the region in the "size" field. "buf" is the buffer

supplied by the userspace application where the read data should be written

to for KVM_S390_MEMOP_LOGICAL_READ, or where the data that should be written

is stored for a KVM_S390_MEMOP_LOGICAL_WRITE. "buf" is unused and can be NULL

when KVM_S390_MEMOP_F_CHECK_ONLY is specified. "ar" designates the access

register number to be used.

field, and the length of the region in the "size" field (which must not

be 0). The maximum value for "size" can be obtained by checking the

KVM_CAP_S390_MEM_OP capability. "buf" is the buffer supplied by the

userspace application where the read data should be written to for

KVM_S390_MEMOP_LOGICAL_READ, or where the data that should be written is

stored for a KVM_S390_MEMOP_LOGICAL_WRITE. When KVM_S390_MEMOP_F_CHECK_ONLY

is specified, "buf" is unused and can be NULL. "ar" designates the access

register number to be used; the valid range is 0..15.

The "reserved" field is meant for future extensions. It is not used by

KVM with the currently defined set of flags.