kvm: attach the exit reason of vcpu as auxstr to KVM_RUN output

kvm: attach the exit reason of vcpu as auxstr to KVM_RUN output

In KVM, a virtual machine implementation like Qemu can access a vcpu
via ioctl.  KVM_RUN is an ioctl command to enter vcpu.  The command
returns control for various reasons: needs of device emulation or
consuming time slices are the typical ones.  The vmi takes a different
action for the reason.

We, strace users, want to know the reason to understand kvm.  This
change prints the reason as auxstr if "-e kvm=vcpu" option is given,
and if strace runs on Linux 4.16.0 or higher, which includes commit
e46b469278a59781f9b25ff608af84892963821b, "kvm: embed vcpu id to dentry
of vcpu anon inode."

The way to get the reason is a bit complicated because the ioctl does
not return it to the userspace directly.  Instead, the vmi and kvm
communicate via an area of the process virtual memory where the fd of
vcpu is mmap'ed.  strace must peek the area to know the reason.

The change does three things: (1) recording the area for the given vcpu
when the target calls VCPU_CREATE to vcpu_info_list per tcb data field,
(2) verifying the data recorded in vcpu_info_list before doing (3), and
(3) decoding the exit reason field of the area.

The change is complicated because there is a case that strace
does not have a chance to do (1) if -p option is used.
In this case, vcpu_info data created in the step (2).

The area has more fields than "exit reason",
dumping them may be implemented in the future.

* defs.h (struct tcb) [HAVE_LINUX_KVM_H]: Add vcpu_info_list field.
[HAVE_LINUX_KVM_H]: (kvm_run_structure_decoder_init,
kvm_vcpu_info_free): New declarations.
* strace.c (usage): Add "kvm" as a new expression for -e option.
(droptcb): Call kvm_vcpu_info_free.
* filter_qualify.c (qualify_kvm): New function calling
kvm_run_structure_decoder_init to enable for attaching the exit
reason to auxstr.
(qual_options): Add "kvm" as an entry.
* xlat/kvm_exit_reason.in: New file.
* kvm.c: Include xmalloc.h and mmap_cache.h.
(dump_kvm_run_structure): New static variable.
(kvm_run_structure_decoder_init): New function.
(vcpu_info): New struct definition representing the 3-tuple: vcpu file
descriptor, id of the vcpu, and mmap'ed entry.
(vcpu_find, vcpu_alloc, vcpu_register, vcpu_getinfo,
kvm_vcpu_info_free): New functions to access tcb's vcpu_info_list
field and vcpu_info data type.
(is_map_for_file, map_len): New helper functions.
(kvm_ioclt_run_attach_auxstr, kvm_ioctl_decode_run): New functions
decoding vcpu exit reason and attaching the decoded data to auxstr
field of tcb.
(kvm_ioctl_create_vcpu): Call vcpu_register to make an entry mapping
a file descriptor and the vcpu id associated with the fd.
(kvm_ioctl): Call kvm_ioctl_decode_run.

Signed-off-by: Masatake YAMATO <yamato@redhat.com>
Co-Authored-by: Dmitry V. Levin <ldv@altlinux.org>