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[Qemu-devel] [PATCH v2 0/5] tcg: Fix mmap_lock assertion failure, take 2

From: Richard Henderson
Subject: [Qemu-devel] [PATCH v2 0/5] tcg: Fix mmap_lock assertion failure, take 2
Date: Tue, 9 Jul 2019 18:36:51 +0200

Changes from v1:
  * Fix whitespace error
  * Fix cpu_lds*_code(), where cut-and-paste failed to extend the data.
    Noticable with check-tcg with docker cross-compiler for cris-linux-user.

Blurb from v1:

While I could not replicate the failure Peter reported, the apparent
root cause -- the old magic fixed page -- should affect other guests
as well.  In particular, the old arm32 magic fixed page at 0xffff0f00,
and the hppa magic fixed page at 0.

In the arm32 and hppa cases that I just mentioned -- but notably not
the x86_64 case that Peter reported -- there is special-case code in
target/*/translate.c to handle those addresses without actually doing
the read from the unmapped address.

Therefore, until we fix these sort of address space representational
errors, we cannot even rely on page_check_range() to validate the
execute access.

Instead, modify the host signal handler to intercept this at SIGSEGV.
At this point we're sure that there is no guest special case that we
have overlooked, because we did attempt the read for execute.

Also, I noticed that we really ought to have some barriers around this
code to make sure that the modifications to helper_retaddr are in fact
visible to the host signal handler.

Also, some minor cleanups to the set of read functions that we expose
for use during translation.

Also, a trivial duplicated condition.


Richard Henderson (5):
  include/qemu/atomic.h: Add signal_barrier
  tcg: Introduce set/clear_helper_retaddr
  tcg: Remove cpu_ld*_code_ra
  tcg: Remove duplicate #if !defined(CODE_ACCESS)
  tcg: Release mmap_lock on translation fault

 include/exec/cpu_ldst.h                   | 20 ++++++
 include/exec/cpu_ldst_useronly_template.h | 40 ++++++++----
 include/qemu/atomic.h                     | 11 ++++
 accel/tcg/user-exec.c                     | 77 ++++++++++++++++-------
 target/arm/helper-a64.c                   |  8 +--
 target/arm/sve_helper.c                   | 43 +++++++------
 6 files changed, 136 insertions(+), 63 deletions(-)


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