[v6,0/6,v5,0/7] RISCV basic exception handling implementation

Message

Oleksii Kurochko May 29, 2023, 12:13 p.m. UTC

The patch series is based on:
    enable MMU for RISC-V [1]
which haven't been commited yet.

The patch series provides a basic implementation of exception handling.
It can do only basic things such as decode a cause of an exception,
save/restore registers and execute "wfi" instruction if an exception
can not be handled.

To verify that exception handling works well it was implemented macros
from <asm/bug.h> such as BUG/WARN/run_in_exception/assert_failed.
The implementation of macros is used "ebreak" instruction and set up bug
frame tables for each type of macros.
Also it was implemented register save/restore to return and continue work
after WARN/run_in_exception.
Not all functionality of the macros was implemented as some of them
require hard-panic the system which is not available now. Instead of
hard-panic 'wfi' instruction is used but it should be definitely changed
in the neareset future.
It wasn't implemented show_execution_state() and stack trace discovering
as it's not necessary now.

[1] https://lore.kernel.org/xen-devel/[e-mail]/T/#t

---
Changes in V6:
 - Update the cover letter message: the patch set is based on MMU patch series.
 - Introduce new patch with temporary printk functionality. ( it will be
   removed when Xen common code will be ready )
 - Change early_printk() to printk().
 - Remove usage of LINK_TO_LOAD() due to the MMU being enabled first.
 - Add additional explanatory comments.
 - Remove patch "xen/riscv: initialize boot_info structure" from the patch
   series.
---
Changes in V5:
 - Rebase on top of [1] and [2]
 - Add new patch which introduces stub for <asm/bug.h> to keep Xen compilable
   as in the patch [xen/riscv: introduce decode_cause() stuff] is used
   header <xen/lib.h> which requires <asm/bug.h>.
 - Remove <xen/error.h> from riscv/traps/c as nothing would require
   inclusion.
 - decode_reserved_interrupt_cause(), decode_interrupt_cause(),
   decode_cause, do_unexpected_trap() were made as static they are expected
   to be used only in traps.c
 - Remove "#include <xen/types.h>" from <asm/bug.h> as there is no any need in it anymore
 - Update macros GET_INSN_LENGTH: remove UL and 'unsigned int len;' from it
 - Remove " include <xen/bug.h>" from risc/setup.c. it is not needed in the current version of
   the patch
 - change an argument type from vaddr_t to uint32_t for is_valid_bugaddr and introduce 
   read_instr() to read instruction properly as the length of qinstruction can be
   either 32 or 16 bits.
 - Code style fixes
 - update the comments before do_bug_frame() in riscv/trap.c
 - [[PATCH v4 5/5] automation: modify RISC-V smoke test ] was dropped as it was provided
   more simple solution by Andrew.  CI: Simplify RISCV smoke testing
 - Refactor is_valid_bugaddr() function.
 - 2 new patches ([PATCH v5 {1-2}/7]) were introduced, the goal of which is to recalculate
   addresses used in traps.c, which can be linker time relative. It is needed as we don't
   have enabled MMU yet.
---
Changes in V4:
  - Rebase the patch series on top of new version of [introduce generic
    implementation of macros from bug.h] patch series.
  - Update the cover letter message as 'Early printk' was merged and
    the current one patch series is based only on [introduce generic
    implementation of macros from bug.h] which hasn't been commited yet.
  - The following patches of the patch series were merged to staging:
      [PATCH v3 01/14] xen/riscv: change ISA to r64G
      [PATCH v3 02/14] xen/riscv: add <asm/asm.h> header
      [PATCH v3 03/14] xen/riscv: add <asm/riscv_encoding.h header
      [PATCH v3 04/14] xen/riscv: add <asm/csr.h> header
      [PATCH v3 05/14] xen/riscv: introduce empty <asm/string.h>
      [PATCH v3 06/14] xen/riscv: introduce empty <asm/cache.h>
      [PATCH v3 07/14] xen/riscv: introduce exception context
      [PATCH v3 08/14] xen/riscv: introduce exception handlers implementation
      [PATCH v3 10/14] xen/riscv: mask all interrupts
  - Fix addressed comments in xen-devel mailing list.

---
Changes in V3:
  - Change the name of config RISCV_ISA_RV64IMA to RISCV_ISA_RV64G
    as instructions from Zicsr and Zifencei extensions aren't part of
    I extension any more.
  - Rebase the patch "xen/riscv: introduce an implementation of macros
    from <asm/bug.h>" on top of patch series [introduce generic implementation
    of macros from bug.h]
  - Update commit messages
---
Changes in V2:
  - take the latest riscv_encoding.h from OpenSBI, update it with Xen
    related changes, and update the commit message with "Origin:"
    tag and the commit message itself.
  - add "Origin:" tag to the commit messag of the patch
    [xen/riscv: add <asm/csr.h> header].
  - Remove the patch [xen/riscv: add early_printk_hnum() function] as the
    functionality provided by the patch isn't used now.
  - Refactor prcoess.h: move structure offset defines to asm-offsets.c,
    change register_t to unsigned long.
  - Refactor entry.S to use offsets defined in asm-offsets.C
  - Rename {__,}handle_exception to handle_trap() and do_trap() to be more
    consistent with RISC-V spec.
  - Merge the pathc which introduces do_unexpected_trap() with the patch
    [xen/riscv: introduce exception handlers implementation].
  - Rename setup_trap_handler() to trap_init() and update correspondingly
    the patches in the patch series.
  - Refactor bug.h, remove bug_instr_t type from it.
  - Refactor decode_trap_cause() function to be more optimization-friendly.
  - Add two new empty headers: <cache.h> and <string.h> as they are needed to
    include <xen/lib.h> which provides ARRAY_SIZE and other macros.
  - Code style fixes.
---

Oleksii Kurochko (6):
  xen/riscv: introduce temporary printk stuff
  xen/riscv: introduce dummy <asm/bug.h>
  xen/riscv: introduce decode_cause() stuff
  xen/riscv: introduce trap_init()
  xen/riscv: introduce an implementation of macros from <asm/bug.h>
  xen/riscv: test basic handling stuff

 xen/arch/riscv/early_printk.c      | 168 ++++++++++++++++++++
 xen/arch/riscv/include/asm/bug.h   |  38 +++++
 xen/arch/riscv/include/asm/traps.h |   1 +
 xen/arch/riscv/setup.c             |  20 +++
 xen/arch/riscv/traps.c             | 238 ++++++++++++++++++++++++++++-
 xen/arch/riscv/xen.lds.S           |  10 ++
 6 files changed, 474 insertions(+), 1 deletion(-)
 create mode 100644 xen/arch/riscv/include/asm/bug.h