[PATCH v2 00/35] Introduce NS8250 UART emulator

[Denis Mukhin via B4 Relay <devnull+dmukhin.ford.com@xxxxxxxxxx>]

The patch series introduces initial in-hypervisor emulator for
NS8250/NS16x50-compatible UARTs under CONFIG_HAS_VUART_NS8250.

In parallel domain creation scenario (hyperlaunch), NS8520 emulator helps
early guest OS bringup debugging, because it eliminates dependency on the
external emulator being operational by the time domains are created. Also,
there's no early console facility similar to vpl011 to support x86 guest OS
bring up.

The NS8250 emulator is disabled by default.

Series
======
- patches 1-11: preparation fixes for xen console and NS8250 emulator.

- patches 12-27: xen console driver cleanup, fixes and preparation for enabling
  physical serial console focus assignment to the guest VM w/ virtual NS8250.

- patches 28-35: initial NS8250 emulator. That adds the I/O port emulator
  for legacy PC COM UARTs, Kconfig option, enabling emulator and libxl
  plumbing.

Limitations
===========
- Only x86;
- Only Linux guest tested so far;
- Only legacy COM{1,2,3,4} resources, no customization;
- Only Xen console as a backend, no inter-domain communication (similar to
  vpl011 on Arm);
- Only 8-bit characters;
- Baud rate is not emulated;
- FIFO-less mode is not emulated properly;
- RX FIFO interrupt moderation (FCR) is not emulated properly, TL16C750
  has special FCR handling;
- No integration w/ VM snapshotting (HVM_REGISTER_SAVE_RESTORE() and
  friends);
- Assumes no ISA-device IRQ sharing;
- MMIO-based UART is not supported.

Testing
=======

Gitlab CI:
  https://gitlab.com/xen-project/people/dmukhin/xen/-/pipelines/1576164352

I tested boot of HVM linux guest w/ OVMF as the virtual firmware.

The emulator, if enabled via CONFIG_HAS_VUART_NS8250=y, will use COM1 (0x3f8)
resources by default.

To test w/ virtual COM1, the guest kernel parameters should contain
  earlycon=uart,io,0x3f8,115200n8 console=uart,io,0x3f8,115200n8

Xen is able to forward physical console input to the domain w/ virtual NS8250.
To switch the console focus press Ctrl+aaa. If console= is given to the HVM
kernel, then the user shall be able to see the login prompt on xen console once
console focus is switched to the HVM guest.

Luca Fancellu helped big time w/ verifying the patch series on arm{32,64} w/
FVP Linux as a guest OS.

Signed-off-by: Denis Mukhin <dmukhin@xxxxxxxx>
---
Changes in v2:
- dropped kmalloc/kfree aliases
- fixed ECLAIR jobs (thanks Andrew Cooper)
- addressed console forwarding on arm32 and arm64 (thanks to Luca Fancellu)
- moved NS8250 debugging stubs into its own patch
- added fix for https://gitlab.com/xen-project/xen/-/issues/184
- Link to v1: 
https://lore.kernel.org/r/20241126-vuart-ns8250-v1-v1-0-87b9a8375b7a@xxxxxxxx

---
Denis Mukhin (35):
      xen: introduce resource.h
      xen/irq: introduce NO_IRQ
      xen/ctype: introduce isconsole()
      arm/vuart: use guest_printk()
      arm/vuart: make domain_has_vuart() public
      riscv/domain: introduce domain_has_vuart()
      ppc/domain: introduce domain_has_vuart()
      x86/domain: introduce domain_has_vuart()
      x86/domain: print emulation_flags
      xen/domain: add get_initial_domain_id()
      xen/domain: enable max_init_domid for all architectures
      xen/console: move vpl011-related code to vpl011 emulator
      xen/console: rename console_input_domain
      xen/console: rename switch_serial_input() to console_find_owner()
      xen/console: rename console_rx to console_owner
      xen/console: introduce printk_common()
      xen/console: introduce consoled_is_enabled()
      xen/console: introduce use of 'is_console' flag
      xen/console: introduce console_set_owner()
      xen/console: introduce console_owner_domid()
      xen/console: introduce console_init_owner()
      xen/console: introduce handle_keypress_in_domain()
      xen/console: introduce console_write()
      xen/console: introduce hwdom_crashconsole=
      xen/console: simplify console owner switch hint
      xen/console: make console buffer size configurable
      xen/console: flush console ring to physical console
      xen/8250-uart: add missing definitions
      x86/hvm: add HVM-specific Kconfig
      x86/hvm: add helpers for raising guest IRQs
      x86/hvm: introduce NS8250 UART emulator
      x86/hvm: add debugging facility to NS8250 UART emulator
      x86/domain: implement domain_has_vuart()
      xen/console: enable console owners w/ emulated NS8250
      docs/misc: update console documentation

 automation/eclair_analysis/ECLAIR/deviations.ecl |    2 +-
 docs/misc/console.txt                            |   50 +-
 docs/misc/xen-command-line.pandoc                |    5 +
 tools/libs/light/libxl_x86.c                     |    6 +-
 tools/ocaml/libs/xc/xenctrl.ml                   |    1 +
 tools/ocaml/libs/xc/xenctrl.mli                  |    1 +
 tools/python/xen/lowlevel/xc/xc.c                |    4 +-
 xen/arch/arm/dom0less-build.c                    |    4 +-
 xen/arch/arm/domain.c                            |   20 +-
 xen/arch/arm/domctl.c                            |    5 +-
 xen/arch/arm/include/asm/domain.h                |    9 +
 xen/arch/arm/include/asm/setup.h                 |    2 -
 xen/arch/arm/include/asm/vpl011.h                |    2 +-
 xen/arch/arm/setup.c                             |    2 -
 xen/arch/arm/vpl011.c                            |   19 +-
 xen/arch/arm/vuart.c                             |    7 +-
 xen/arch/ppc/include/asm/domain.h                |    2 +
 xen/arch/ppc/include/asm/setup.h                 |    2 -
 xen/arch/riscv/include/asm/domain.h              |    2 +
 xen/arch/riscv/include/asm/setup.h               |    2 -
 xen/arch/x86/Kconfig                             |   66 +-
 xen/arch/x86/dom0_build.c                        |    2 +
 xen/arch/x86/domain.c                            |   16 +-
 xen/arch/x86/hvm/Kconfig                         |   77 ++
 xen/arch/x86/hvm/Makefile                        |    1 +
 xen/arch/x86/hvm/hvm.c                           |   16 +-
 xen/arch/x86/hvm/irq.c                           |   24 +
 xen/arch/x86/hvm/vuart_ns8250.c                  | 1008 ++++++++++++++++++++++
 xen/arch/x86/include/asm/domain.h                |    8 +-
 xen/arch/x86/include/asm/hvm/domain.h            |    5 +
 xen/arch/x86/include/asm/hvm/irq.h               |    3 +
 xen/arch/x86/include/asm/hvm/vuart_ns8250.h      |   75 ++
 xen/arch/x86/include/asm/pv/shim.h               |    4 +-
 xen/arch/x86/include/asm/setup.h                 |    2 -
 xen/arch/x86/pv/shim.c                           |    6 +-
 xen/common/device-tree/device-tree.c             |   21 +-
 xen/common/domain.c                              |   35 +-
 xen/drivers/char/Kconfig                         |   23 +
 xen/drivers/char/console.c                       |  394 +++++----
 xen/drivers/char/consoled.c                      |   18 +-
 xen/drivers/passthrough/arm/smmu.c               |   15 +-
 xen/include/public/arch-x86/xen.h                |   14 +-
 xen/include/xen/8250-uart.h                      |   81 +-
 xen/include/xen/console.h                        |    4 +-
 xen/include/xen/consoled.h                       |   35 +-
 xen/include/xen/ctype.h                          |    3 +
 xen/include/xen/domain.h                         |    5 +
 xen/include/xen/irq.h                            |    1 +
 xen/include/xen/lib.h                            |    3 +
 xen/include/xen/resource.h                       |   40 +
 50 files changed, 1799 insertions(+), 353 deletions(-)
---
base-commit: dc8e1b33a525d31989c0d1ffe6ae7794484e1d99
change-id: 20241205-vuart-ns8250-45847bc04140

Best regards,
-- 
Denis Mukhin <dmukhin@xxxxxxxx>