Speed up indirect branches by jumping to the target if it is valid.

Softmmu measurements (see later commit for user-mode numbers):

Note: baseline (i.e. speedup == 1x) is QEMU v2.9.0.

-                  SPECint06 (test set), x86_64-softmmu (Ubuntu 16.04 guest). Host: Intel i7-4790K @ 4.00GHz

 2.4x +-+--------------------------------------------------------------------------------------------------------------+-+
      |                                                                                                                  |
      |   cross                                                                                                          |
 2.2x +cross+jr..........................................................................+++...........................+-+
      |                                                                                   |                              |
      |                                                                               +++ |                              |
   2x +-+..............................................................................|..|............................+-+
      |                                                                                |  |                              |
      |                                                                                |  |                              |
 1.8x +-+..............................................................................|####...........................+-+
      |                                                                                |# |#                             |
      |                                                                              **** |#                             |
 1.6x +-+............................................................................*.|*.|#...........................+-+
      |                                                                              * |* |#                             |
      |                                                                              * |* |#                             |
 1.4x +-+.......................................................................+++..*.|*.|#...........................+-+
      |                                                      ++++++             #### * |*++#             +++             |
      |                        +++                            |  |              #++# *++*  #          +++ |              |
 1.2x +-+......................###.....####....+++............|..|...........****..#.*..*..#....####...|.###.....####..+-+
      |        +++          **** #  ****  #    ####          ***###          *++*  # *  *  #    #++#  ****|#  +++#++#    |
      |    ****###     +++  *++* #  *++*  #  ++#  #    ####  *|* |#     +++  *  *  # *  *  #  ***  #  *| *|#  ****  #    |
   1x +-++-*++*++#++***###++*++*+#++*+-*++#+****++#++***++#+-*+*++#-+****##++*++*-+#+*++*-+#++*+*++#++*-+*+#++*++*++#-++-+
      |    *  *  #  * *  #  *  * #  *  *  # *  *  #  * *  #  *|* |#  *++* #  *  *  # *  *  #  * *  #  *  * #  *  *  #    |
      |    *  *  #  * *  #  *  * #  *  *  # *  *  #  * *  #  *+*++#  *  * #  *  *  # *  *  #  * *  #  *  * #  *  *  #    |
 0.8x +-+--****###--***###--****##--****###-****###--***###--***###--****##--****###-****###--***###--****##--****###--+-+
         astar   bzip2      gcc   gobmk h264ref   hmmlibquantum      mcf omnetpperlbench   sjengxalancbmk   hmean
  png: http://imgur.com/DU36YFU

NB. 'cross' represents the previous commit.
Reviewed-by: NAlex Bennée <alex.bennee@linaro.org>
Reviewed-by: NRichard Henderson <rth@twiddle.net>
Signed-off-by: NEmilio G. Cota <cota@braap.org>
Message-Id: <1493263764-18657-11-git-send-email-cota@braap.org>
Signed-off-by: NRichard Henderson <rth@twiddle.net>

Instead of unconditionally exiting to the exec loop, use the
gen_jr helper to jump to the target if it is valid.

Perf impact: see next commit's log.
Reviewed-by: NRichard Henderson <rth@twiddle.net>
Signed-off-by: NEmilio G. Cota <cota@braap.org>
Message-Id: <1493263764-18657-10-git-send-email-cota@braap.org>
Signed-off-by: NRichard Henderson <rth@twiddle.net>

This helper will be used by subsequent changes.
Reviewed-by: NAlex Bennée <alex.bennee@linaro.org>
Signed-off-by: NEmilio G. Cota <cota@braap.org>
Message-Id: <1493263764-18657-9-git-send-email-cota@braap.org>
Signed-off-by: NRichard Henderson <rth@twiddle.net>

Speed up indirect branches by jumping to the target if it is valid.

Softmmu measurements (see later commit for user-mode results):

Note: baseline (i.e. speedup == 1x) is QEMU v2.9.0.

- Impact on Boot time

| setup  | ARM debian jessie boot+shutdown time | stddev |
|--------+--------------------------------------+--------|
| v2.9.0 |                                 8.84 |   0.07 |
| +cross |                                 8.85 |   0.03 |
| +jr    |                                 8.83 |   0.06 |

-                            NBench, arm-softmmu (debian jessie guest). Host: Intel i7-4790K @ 4.00GHz

  1.3x +-+-------------------------------------------------------------------------------------------------------------+-+
       |                                                                                                                 |
       |   cross                                                          ####                                           |
 1.25x +cross+jr..........................................................#++#.........................................+-+
       |                                                        ####      #  #                                           |
       |                                                     +++#  #      #  #                                           |
       |                                      +++            ****  #      #  #                                           |
  1.2x +-+...................................####............*..*..#......#..#.........................................+-+
       |                                  ****  #            *  *  #      #  #     ####                                  |
       |                                  *  *  #            *  *  #      #  #     #  #                                  |
 1.15x +-+................................*..*..#............*..*..#......#..#.....#..#................................+-+
       |                                  *  *  #            *  *  #      #  #     #  #                                  |
       |                                  *  *  #      ####  *  *  #      #  #     #  #                                  |
       |                                  *  *  #      #  #  *  *  #      #  #     #  #                         ####     |
  1.1x +-+................................*..*..#......#..#..*..*..#......#..#.....#..#.........................#..#...+-+
       |                                  *  *  #      #  #  *  *  #      #  #     #  #                         #  #     |
       |                                  *  *  #      #  #  *  *  #      #  #     #  #                         #  #     |
 1.05x +-+..........................####..*..*..#......#..#..*..*..#......#..#.....#..#......+++............*****..#...+-+
       |                        *****  #  *  *  #      #  #  *  *  #  *****  #     #  #   +++ |    ****###  *   *  #     |
       |                        *+++*  #  *  *  #      #  #  *  *  #  *+++*  #  ****  #  *****###  *  *  #  *   *  #     |
       |     *****###  +++####  *   *  #  *  *  #  *****  #  *  *  #  *   *  #  *  *  #  * | *++#  *  *  #  *   *  #     |
    1x +-++-+*+++*-+#++****++#++*+-+*++#+-*++*++#-+*+++*-+#++*++*++#++*+-+*++#+-*++*++#-+*+++*-+#++*++*++#++*+-+*++#+-++-+
       |     *   *  #  *  *  #  *   *  #  *  *  #  *   *  #  *  *  #  *   *  #  *  *  #  *   *  #  *  *  #  *   *  #     |
       |     *   *  #  *  *  #  *   *  #  *  *  #  *   *  #  *  *  #  *   *  #  *  *  #  *   *  #  *  *  #  *   *  #     |
 0.95x +-+---*****###--****###--*****###--****###--*****###--****###--*****###--****###--*****###--****###--*****###---+-+
       ASSIGNMENT BITFIELD   FOURFP EMULATION   HUFFMAN   LU DECOMPOSITIONEURAL NNUMERIC SOSTRING SORT     hmean
  png: http://imgur.com/eOLmZNR

NB. 'cross' represents the previous commit.
Signed-off-by: NEmilio G. Cota <cota@braap.org>
Message-Id: <1493263764-18657-8-git-send-email-cota@braap.org>
[rth: Replace gen_jr global variable with DISAS_EXIT state.]
Signed-off-by: NRichard Henderson <rth@twiddle.net>

Instead of unconditionally exiting to the exec loop, use the
lookup_and_goto_ptr helper to jump to the target if it is valid.

Perf impact: see next commit's log.
Reviewed-by: NAlex Bennée <alex.bennee@linaro.org>
Reviewed-by: NRichard Henderson <rth@twiddle.net>
Signed-off-by: NEmilio G. Cota <cota@braap.org>
Message-Id: <1493263764-18657-7-git-send-email-cota@braap.org>
Signed-off-by: NRichard Henderson <rth@twiddle.net>

Suggested-by: NRichard Henderson <rth@twiddle.net>
Reviewed-by: NRichard Henderson <rth@twiddle.net>
Signed-off-by: NEmilio G. Cota <cota@braap.org>
Message-Id: <1493263764-18657-6-git-send-email-cota@braap.org>
[rth: Reuse goto_ptr epilogue for exit_tb 0.]
Signed-off-by: NRichard Henderson <rth@twiddle.net>

Instead of exporting goto_ptr directly to TCG frontends, export
tcg_gen_lookup_and_goto_ptr(), which calls goto_ptr with the pointer
returned by the lookup_tb_ptr() helper. This is the only use case
we have for goto_ptr and lookup_tb_ptr, so having this function is
very convenient. Furthermore, it trivially allows us to avoid calling
the lookup helper if goto_ptr is not implemented by the backend.
Reviewed-by: NAlex Bennée <alex.bennee@linaro.org>
Signed-off-by: NEmilio G. Cota <cota@braap.org>
Message-Id: <1493263764-18657-2-git-send-email-cota@braap.org>
Message-Id: <1493263764-18657-3-git-send-email-cota@braap.org>
Message-Id: <1493263764-18657-4-git-send-email-cota@braap.org>
Message-Id: <1493263764-18657-5-git-send-email-cota@braap.org>
[rth: Squashed 4 related commits.]
Signed-off-by: NRichard Henderson <rth@twiddle.net>

We need to coordinate with the TCG_OVERSIZED_GUEST test in cputlb.c,
and allow 64-bit atomics even though sizeof(void *) == 4.
Reviewed-by: NAlex Bennée <alex.bennee@linaro.org>
Signed-off-by: NRichard Henderson <rth@twiddle.net>

We have required a v9 cpu since 9b9c37c3.
However, the flags we were using did not reliably enable v8plus, which
meant that the compiler didn't know it could inline 64-bit atomics.
Reviewed-by: NAlex Bennée <alex.bennee@linaro.org>
Signed-off-by: NRichard Henderson <rth@twiddle.net>

Avoid a "cast from pointer to integer of different size" warning
by using the proper host type.
Reviewed-by: NPhilippe Mathieu-Daudé <f4bug@amsat.org>
Reviewed-by: NAlex Bennée <alex.bennee@linaro.org>
Signed-off-by: NRichard Henderson <rth@twiddle.net>

trivial patches for 2017-06-05

# gpg: Signature made Mon 05 Jun 2017 15:23:46 BST
# gpg:                using RSA key 0x701B4F6B1A693E59
# gpg: Good signature from "Michael Tokarev <mjt@tls.msk.ru>"
# gpg:                 aka "Michael Tokarev <mjt@corpit.ru>"
# gpg:                 aka "Michael Tokarev <mjt@debian.org>"
# Primary key fingerprint: 6EE1 95D1 886E 8FFB 810D  4324 457C E0A0 8044 65C5
#      Subkey fingerprint: 7B73 BAD6 8BE7 A2C2 8931  4B22 701B 4F6B 1A69 3E59

* remotes/mjt/tags/trivial-patches-fetch: (21 commits)
  hw/core: nmi.c can be compiled as common-obj nowadays
  dump: fix memory_mapping_filter leak
  ide-test: check return of fwrite
  help: Add newline to end of thread option help text
  qemu-ga: remove useless allocation
  scsi/lsi53c895a: Remove unused lsi_mem_*() return value
  qapi: Fix some QMP documentation regressions
  hw/mips: add missing include
  register: display register prefix (name) since it is available
  hw/sparc: use ARRAY_SIZE() macro
  hw/xtensa: sim: use g_string/g_new
  target/arm: add data cache invalidation cp15 instruction to cortex-r5
  block: Correct documentation for BLOCK_WRITE_THRESHOLD
  trivial: Remove unneeded ifndef in memory.h
  altera_timer: fix incorrect memset
  configure: Detect native NetBSD curses(3)
  tests/libqtest: Print error instead of aborting when env variable is missing
  docs/qdev-device-use.txt: update section Default Devices
  docs qemu-doc: Avoid ide-drive, it's deprecated
  qemu-doc: Add hyperlinks to further license information
  ...
Signed-off-by: NPeter Maydell <peter.maydell@linaro.org>

The target-specific code in nmi.c has been removed with this commit:

	commit f7e981f2
	nmi: remove x86 specific nmi handling
Signed-off-by: NThomas Huth <thuth@redhat.com>
Reviewed-by: NJuan Quintela <quintela@redhat.com>
Signed-off-by: NMichael Tokarev <mjt@tls.msk.ru>

# gpg: Signature made Fri 02 Jun 2017 20:12:48 BST
# gpg:                using RSA key 0xDAE8E10975969CE5
# gpg: Good signature from "Marc-André Lureau <marcandre.lureau@redhat.com>"
# gpg:                 aka "Marc-André Lureau <marcandre.lureau@gmail.com>"
# gpg: WARNING: This key is not certified with sufficiently trusted signatures!
# gpg:          It is not certain that the signature belongs to the owner.
# Primary key fingerprint: 87A9 BD93 3F87 C606 D276  F62D DAE8 E109 7596 9CE5

* remotes/elmarco/tags/chrfe-pull-request:
  char: move char devices to chardev/
  char: make chr_fe_deinit() optionaly delete backend
  char: rename functions that are not part of fe
  char: move CharBackend handling in char-fe unit
  char: generalize qemu_chr_write_all()
  be-hci: use backend functions
  chardev: serial & parallel declaration to own headers
  chardev: move headers to include/chardev
  Remove/replace sysemu/char.h inclusion
  char-win: close file handle except with console
  char-win: rename hcom->file
  char-win: rename win_chr_init/poll win_chr_serial_init/poll
  char-win: remove WinChardev.len
  char-win: simplify win_chr_read()
  char: cast ARRAY_SIZE() as signed to silent warning on empty array
Signed-off-by: NPeter Maydell <peter.maydell@linaro.org>

Spotted by ASAN.
Signed-off-by: NMarc-André Lureau <marcandre.lureau@redhat.com>
Signed-off-by: NMichael Tokarev <mjt@tls.msk.ru>

To quiet patchew, add an assert for fwrite's return value.
Signed-off-by: NJohn Snow <jsnow@redhat.com>
Reviewed-by: NJeff Cody <jcody@redhat.com>
Reviewed-by: NLaurent Vivier <lvivier@redhat.com>
Signed-off-by: NMichael Tokarev <mjt@tls.msk.ru>

The help text for the thread sub option of the accel option is missing
a newline at the end. This is annoying as it makes it hard to see the
help text for the next option.

Add the new line so that the following option help text (-smp) is
displayed on a new line rather on the same line and directly after
the thread help.

Before patch:

-accel [accel=]accelerator[,thread=single|multi]
                select accelerator (kvm, xen, hax or tcg; use 'help' for a list)
                thread=single|multi (enable multi-threaded TCG)-smp [cpus=]n[,maxcpus=cpus][,cores=cores][,threads=threads][,sockets=sockets]
                set the number of CPUs to 'n' [default=1]
                maxcpus= maximum number of total cpus, including
                offline CPUs for hotplug, etc
                cores= number of CPU cores on one socket
                threads= number of threads on one CPU core
                sockets= number of discrete sockets in the system

After patch:

-accel [accel=]accelerator[,thread=single|multi]
                select accelerator (kvm, xen, hax or tcg; use 'help' for a list)
                thread=single|multi (enable multi-threaded TCG)
-smp [cpus=]n[,maxcpus=cpus][,cores=cores][,threads=threads][,sockets=sockets]
                set the number of CPUs to 'n' [default=1]
                maxcpus= maximum number of total cpus, including
                offline CPUs for hotplug, etc
                cores= number of CPU cores on one socket
                threads= number of threads on one CPU core
                sockets= number of discrete sockets in the system
Signed-off-by: NSuraj Jitindar Singh <sjitindarsingh@gmail.com>
Signed-off-by: NMichael Tokarev <mjt@tls.msk.ru>

There is no need to duplicate a fixed string.
Signed-off-by: NMarc-André Lureau <marcandre.lureau@redhat.com>
Reviewed-by: NEric Blake <eblake@redhat.com>
Reviewed-by: NPhilippe Mathieu-Daudé <f4bug@amsat.org>
Signed-off-by: NMichael Tokarev <mjt@tls.msk.ru>

lsi_mem_read/write() always return 0 about which their
callers actually don't care. Change the function type
to void.
Signed-off-by: NMao Zhongyi <maozy.fnst@cn.fujitsu.com>
Signed-off-by: NMichael Tokarev <mjt@tls.msk.ru>

In the process of getting rid of docs/qmp-commands.txt, we managed
to regress on some of the text that changed after the point where
the move was first branched and when the move actually occurred.
For example, commit 3282eca4 for blockdev-snapshot re-added the
extra "options" layer which had been cleaned up in commit 0153d2f5.

This clears up all regressions identified over the range
02b351d8..bd6092e4:
https://lists.gnu.org/archive/html/qemu-devel/2017-05/msg05127.html
as well as a cleanup to x-blockdev-remove-medium to prefer
'id' over 'device' (matching the cleanup for 'eject').
Signed-off-by: NEric Blake <eblake@redhat.com>
Reviewed-by: NMarkus Armbruster <armbru@redhat.com>
Signed-off-by: NMichael Tokarev <mjt@tls.msk.ru>

Signed-off-by: NPhilippe Mathieu-Daudé <f4bug@amsat.org>
Acked-by: NAurelien Jarno <aurelien@aurel32.net>
Signed-off-by: NMichael Tokarev <mjt@tls.msk.ru>

Signed-off-by: NPhilippe Mathieu-Daudé <f4bug@amsat.org>
Reviewed-by: NAlistair Francis <alistair.francis@xilinx.com>
Signed-off-by: NMichael Tokarev <mjt@tls.msk.ru>

Signed-off-by: NPhilippe Mathieu-Daudé <f4bug@amsat.org>
Reviewed-by: NAlex Bennée <alex.bennee@linaro.org>
Signed-off-by: NMichael Tokarev <mjt@tls.msk.ru>

Replace malloc/free/sprintf with g_string/g_string_printf/g_string_free.
Replace g_malloc with g_new when allocating the MemoryRegion to get more
type safety.
Suggested-by: NAlex Bennée <alex.bennee@linaro.org>
Signed-off-by: NMax Filippov <jcmvbkbc@gmail.com>
Reviewed-by: NPhilippe Mathieu-Daudé <f4bug@amsat.org>
Signed-off-by: NMichael Tokarev <mjt@tls.msk.ru>

The cp15, CRn=15, opc1=0, CRm=5, opc2=0 instruction invalidates all the
data cache on the cortex-r5. Implementing it as a NOP.
Signed-off-by: NLuc MICHEL <luc.michel@git.antfield.fr>
Signed-off-by: NMichael Tokarev <mjt@tls.msk.ru>

Use the correct command name.
Signed-off-by: NEric Blake <eblake@redhat.com>
Signed-off-by: NMichael Tokarev <mjt@tls.msk.ru>

All the file is surounded already by #ifndef CONFIG_USER_ONLY.
Signed-off-by: NJuan Quintela <quintela@redhat.com>
Reviewed-by: NDr. David Alan Gilbert <dgilbert@redhat.com>
Reviewed-by: NLaurent Vivier <lvivier@redhat.com>
Signed-off-by: NMichael Tokarev <mjt@tls.msk.ru>

Use sizeof instead of ARRAY_SIZE, fixing -Wmemset-elt-size with recent
GCC versions.
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>
Reviewed-by: NLaurent Vivier <lvivier@redhat.com>
Signed-off-by: NMichael Tokarev <mjt@tls.msk.ru>

NetBSD ships with traditional BSD curses with compatibility with ncurses.
qemu works nicely with the basesystem version of curses(3) from NetBSD.

The only mismatch between curses(3) and ncurses is the lack of
curses_version() in the NetBSD version. This function is used solely in
the configure script, therefore eliminate it from the curses(3) detection.

With this change applied, configure detects correctly curses frontend.
Signed-off-by: NKamil Rytarowski <n54@gmx.com>
Reviewed-by: NAlex Bennée <alex.bennee@linaro.org>
Reviewed-by: NPhilippe Mathieu-Daudé <f4bug@amsat.org>
Signed-off-by: NMichael Tokarev <mjt@tls.msk.ru>

When you currently try to run a test directly from the command line
without setting the QTEST_QEMU_BINARY environment variable first,
you are presented with an unhelpful assertion message like this:

 ERROR:tests/libqtest.c:163:qtest_init_without_qmp_handshake:
 assertion failed: (qemu_binary != NULL)
 Aborted (core dumped)

Let's replace the assert() with a more user friendly error message
instead.
Reviewed-by: NMarkus Armbruster <armbru@redhat.com>
Signed-off-by: NThomas Huth <thuth@redhat.com>
Signed-off-by: NMichael Tokarev <mjt@tls.msk.ru>

Resynchronize the table of default device suppressions with vl.c's
default_list[].
Signed-off-by: NMarkus Armbruster <armbru@redhat.com>
Reviewed-by: NThomas Huth <thuth@redhat.com>
Signed-off-by: NMichael Tokarev <mjt@tls.msk.ru>

Suggested-by: NThomas Huth <thuth@redhat.com>
Signed-off-by: NMarkus Armbruster <armbru@redhat.com>
Reviewed-by: NThomas Huth <thuth@redhat.com>
Signed-off-by: NMichael Tokarev <mjt@tls.msk.ru>

Add a link to the GPLv2 and a link to the LICENSE file in the
QEMU repository to fix the two TODO items in this appendix.
Signed-off-by: NThomas Huth <thuth@redhat.com>
Reviewed-by: NStefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: NMichael Tokarev <mjt@tls.msk.ru>

The qemu-ga description is currently a subsection of the Disk Images
chapter - which does not make much sense since the qemu-ga is not
directly related to disk images. So let's move this information
into a separate chapter instead.
Signed-off-by: NThomas Huth <thuth@redhat.com>
Reviewed-by: NStefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: NMichael Tokarev <mjt@tls.msk.ru>

virtio, vhost: fixes, features

IOTLB support in vhost-user.
A bunch of fixes all over the place.
Signed-off-by: NMichael S. Tsirkin <mst@redhat.com>

# gpg: Signature made Fri 02 Jun 2017 17:33:25 BST
# gpg:                using RSA key 0x281F0DB8D28D5469
# gpg: Good signature from "Michael S. Tsirkin <mst@kernel.org>"
# gpg:                 aka "Michael S. Tsirkin <mst@redhat.com>"
# Primary key fingerprint: 0270 606B 6F3C DF3D 0B17  0970 C350 3912 AFBE 8E67
#      Subkey fingerprint: 5D09 FD08 71C8 F85B 94CA  8A0D 281F 0DB8 D28D 5469

* remotes/mst/tags/for_upstream:
  spec/vhost-user spec: Add IOMMU support
  vhost-user: add slave-req-fd support
  vhost-user: add vhost_user to hold the chr
  vhost: rework IOTLB messaging
  vhost: propagate errors in vhost_device_iotlb_miss()
  virtio-serial: fix segfault on disconnect
  virtio: add virtqueue_alloc_element tracepoint
  virtio-serial-bus: Unset hotplug handler when unrealize
Signed-off-by: NPeter Maydell <peter.maydell@linaro.org>

This patch specifies and implements the master/slave communication
to support device IOTLB in slave.

The vhost_iotlb_msg structure introduced for kernel backends is
re-used, making the design close between the two backends.

An exception is the use of the secondary channel to enable the
slave to send IOTLB miss requests to the master.
Signed-off-by: NMaxime Coquelin <maxime.coquelin@redhat.com>
Reviewed-by: NMichael S. Tsirkin <mst@redhat.com>
Signed-off-by: NMichael S. Tsirkin <mst@redhat.com>

Learn to give a socket to the slave to let him make requests to the
master.
Signed-off-by: NMarc-André Lureau <marcandre.lureau@redhat.com>
Signed-off-by: NMaxime Coquelin <maxime.coquelin@redhat.com>
Reviewed-by: NMichael S. Tsirkin <mst@redhat.com>
Signed-off-by: NMichael S. Tsirkin <mst@redhat.com>

Next patches will add more fields to the structure
Signed-off-by: NMarc-André Lureau <marcandre.lureau@redhat.com>
Signed-off-by: NMaxime Coquelin <maxime.coquelin@redhat.com>
Reviewed-by: NMichael S. Tsirkin <mst@redhat.com>
Signed-off-by: NMichael S. Tsirkin <mst@redhat.com>

This patch reworks IOTLB messaging to prepare for vhost-user
device IOTLB support.

IOTLB messages handling is extracted from vhost-kernel backend,
so that only the messages transport remains backend specifics.
Signed-off-by: NMaxime Coquelin <maxime.coquelin@redhat.com>
Reviewed-by: NMichael S. Tsirkin <mst@redhat.com>
Signed-off-by: NMichael S. Tsirkin <mst@redhat.com>

Some backends might want to know when things went wrong.
Signed-off-by: NMaxime Coquelin <maxime.coquelin@redhat.com>
Reviewed-by: NMichael S. Tsirkin <mst@redhat.com>
Signed-off-by: NMichael S. Tsirkin <mst@redhat.com>

Since commit d4c19cde ("virtio-serial:
add missing virtio_detach_element() call") the following commands may
cause QEMU to segfault:

  $ qemu -M accel=kvm -cpu host -m 1G \
         -drive if=virtio,file=test.img,format=raw \
         -device virtio-serial-pci,id=virtio-serial0 \
         -chardev socket,id=channel1,path=/tmp/chardev.sock,server,nowait \
         -device virtserialport,chardev=channel1,bus=virtio-serial0.0,id=port1
  $ nc -U /tmp/chardev.sock
  ^C

  (guest)$ cat /dev/zero >/dev/vport0p1

The segfault is non-deterministic: if the event loop notices the socket
has been closed then there is no crash.  The disconnect has to happen
right before QEMU attempts to write data to the socket.

The backtrace is as follows:

  Thread 1 "qemu-system-x86" received signal SIGSEGV, Segmentation fault.
  0x00005555557e0698 in do_flush_queued_data (port=0x5555582cedf0, vq=0x7fffcc854290, vdev=0x55555807b1d0) at hw/char/virtio-serial-bus.c:180
  180           for (i = port->iov_idx; i < port->elem->out_num; i++) {
  #1  0x000055555580d363 in virtio_queue_notify_vq (vq=0x7fffcc854290) at hw/virtio/virtio.c:1524
  #2  0x000055555580d363 in virtio_queue_host_notifier_read (n=0x7fffcc8542f8) at hw/virtio/virtio.c:2430
  #3  0x0000555555b3482c in aio_dispatch_handlers (ctx=ctx@entry=0x5555566b8c80) at util/aio-posix.c:399
  #4  0x0000555555b350d8 in aio_dispatch (ctx=0x5555566b8c80) at util/aio-posix.c:430
  #5  0x0000555555b3212e in aio_ctx_dispatch (source=<optimized out>, callback=<optimized out>, user_data=<optimized out>) at util/async.c:261
  #6  0x00007fffde71de52 in g_main_context_dispatch () at /lib64/libglib-2.0.so.0
  #7  0x0000555555b34353 in glib_pollfds_poll () at util/main-loop.c:213
  #8  0x0000555555b34353 in os_host_main_loop_wait (timeout=<optimized out>) at util/main-loop.c:261
  #9  0x0000555555b34353 in main_loop_wait (nonblocking=<optimized out>) at util/main-loop.c:517
  #10 0x0000555555773207 in main_loop () at vl.c:1917
  #11 0x0000555555773207 in main (argc=<optimized out>, argv=<optimized out>, envp=<optimized out>) at vl.c:4751

The do_flush_queued_data() function does not anticipate chardev close
events during vsc->have_data().  It expects port->elem to remain
non-NULL for the duration its for loop.

The fix is simply to return from do_flush_queued_data() if the port
closes because the close event already frees port->elem and drains the
virtqueue - there is nothing left for do_flush_queued_data() to do.
Reported-by: NSitong Liu <siliu@redhat.com>
Reported-by: NMin Deng <mdeng@redhat.com>
Signed-off-by: NStefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: NMichael S. Tsirkin <mst@redhat.com>
Signed-off-by: NMichael S. Tsirkin <mst@redhat.com>