[PATCH v8 04/12] drm/i915: return EACCES for check_cmd() failures

[sourab gupta]

On Thu, 2016-10-27 at 19:14 -0700, Robert Bragg wrote:
> check_cmd() is checking whether a command adheres to certain
> restrictions that ensure it's safe to execute within a privileged batch
> buffer. Returning false implies a privilege problem, not that the
> command is invalid.
> 
> The distinction makes the difference between allowing the buffer to be
> executed as an unprivileged batch buffer or returning an EINVAL error to
> userspace without executing anything.
> 
> In a case where userspace may want to test whether it can successfully
> write to a register that needs privileges the distinction may be
> important and an EINVAL error may be considered fatal.
> 
> In particular this is currently true for Mesa, which includes a test for
> whether OACONTROL can be written too, but Mesa treats any error when
> flushing a batch buffer as fatal, calling exit(1).
> 
> As it is currently Mesa can gracefully handle a failure to write to
> OACONTROL if the command parser is disabled, but if we were to remove
> OACONTROL from the parser's whitelist then the returned EINVAL would
> break Mesa applications as they attempt an OACONTROL write.
> 
> This bumps the command parser version from 7 to 8, as the change is
> visible to userspace.
> 
> Signed-off-by: Robert Bragg <robert at sixbynine.org>
> Reviewed-by: Matthew Auld <matthew.auld at intel.com>
Well, looks reasonable to me.

Reviewed-by: Sourab Gupta <sourab.gupta at intel.com>