[Qemu-commits] [qemu/qemu] d00960: Revert "arm/kvm: add support for MTE"

[Peter Maydell]

  Branch: refs/heads/master
  Home:   https://github.com/qemu/qemu
  Commit: d009607d08d22f91ca399b72828c6693855e7325
      
https://github.com/qemu/qemu/commit/d009607d08d22f91ca399b72828c6693855e7325
  Author: Peter Maydell <peter.maydell@linaro.org>
  Date:   2023-05-19 (Fri, 19 May 2023)

  Changed paths:
    M hw/arm/virt.c
    M target/arm/cpu.c
    M target/arm/cpu.h
    M target/arm/kvm.c
    M target/arm/kvm64.c
    M target/arm/kvm_arm.h

  Log Message:
  -----------
  Revert "arm/kvm: add support for MTE"

This reverts commit b320e21c48ce64853904bea6631c0158cc2ef227,
which accidentally broke TCG, because it made the TCG -cpu max
report the presence of MTE to the guest even if the board hadn't
enabled MTE by wiring up the tag RAM. This meant that if the guest
then tried to use MTE QEMU would segfault accessing the
non-existent tag RAM:

    ==346473==ERROR: UndefinedBehaviorSanitizer: SEGV on unknown address (pc 
0x55f328952a4a bp 0x00000213a400 sp 0x7f7871859b80 T346476)
    ==346473==The signal is caused by a READ memory access.
    ==346473==Hint: this fault was caused by a dereference of a high value 
address (see register values below).  Disassemble the provided pc to learn 
which register was used.
        #0 0x55f328952a4a in address_space_to_flatview 
/mnt/nvmedisk/linaro/qemu-from-laptop/qemu/include/exec/memory.h:1108:12
        #1 0x55f328952a4a in address_space_translate 
/mnt/nvmedisk/linaro/qemu-from-laptop/qemu/include/exec/memory.h:2797:31
        #2 0x55f328952a4a in allocation_tag_mem 
/mnt/nvmedisk/linaro/qemu-from-laptop/qemu/build/arm-clang/../../target/arm/tcg/mte_helper.c:176:10
        #3 0x55f32895366c in helper_stgm 
/mnt/nvmedisk/linaro/qemu-from-laptop/qemu/build/arm-clang/../../target/arm/tcg/mte_helper.c:461:15
        #4 0x7f782431a293  (<unknown module>)

It's also not clear that the KVM logic is correct either:
MTE defaults to on there, rather than being only on if the
board wants it on.

Revert the whole commit for now so we can sort out the issues.

(We didn't catch this in CI because we have no test cases in
avocado that use guests with MTE support.)

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Message-Id: <20230519145808.348701-1-peter.maydell@linaro.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>