[Bug 1880722] Re: Problems related to checking page crossing in use_goto_tb()

[Ahmed Karaman]

** Summary changed:

- Changing executable page permissions with mmap causes user-mode failures
+ Problems related to checking page crossing in use_goto_tb()

** Description changed:

- The discussion that led to this bug discovery can be found in this 
+ The discussion that led to this bug discovery can be found in this
  mailing list thread:
  https://lists.nongnu.org/archive/html/qemu-devel/2020-05/msg05426.html
  
- A workaround for this problem would be to check for page crossings for 
- both the user and system modes in the use_goto_tb() function across 
+ A workaround for this problem would be to check for page crossings for
+ both the user and system modes in the use_goto_tb() function across
  targets. Some targets like "hppa" already implement this fix but others
  don't.
  
- To solve the root cause of this problem, the linux-user/mmap.c should 
- be fixed to do all the invalidations required. By doing so, up to 6.93% 
- performance improvements will be achieved.
+ To solve the root cause of this problem, the linux-user/mmap.c should
+ be fixed to do all the invalidations required. By doing so, better
+ performance results could be achieved, compared to the case of the
+ workaround described above.

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https://bugs.launchpad.net/bugs/1880722

Title:
  Problems related to checking page crossing in use_goto_tb()

Status in QEMU:
  New

Bug description:
  The discussion that led to this bug discovery can be found in this
  mailing list thread:
  https://lists.nongnu.org/archive/html/qemu-devel/2020-05/msg05426.html

  A workaround for this problem would be to check for page crossings for
  both the user and system modes in the use_goto_tb() function across
  targets. Some targets like "hppa" already implement this fix but others
  don't.

  To solve the root cause of this problem, the linux-user/mmap.c should
  be fixed to do all the invalidations required. By doing so, better
  performance results could be achieved, compared to the case of the
  workaround described above.

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