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[IA64] fix syscall-optimization goof

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Sadly, I goofed in this syscall-tuning patch:

ChangeSet 1.1966.1.40 2005/01/22 13:31:05 davidm@hpl.hp.com
  [IA64] Improve ia64_leave_syscall() for McKinley-type cores.

  Optimize ia64_leave_syscall() a bit better for McKinley-type cores.
  The patch looks big, but that's mostly due to renaming r16/r17 to r2/r3.
  Good for a 13 cycle improvement.

The problem is that the size of the physical stacked registers was
loaded into the wrong register (r3 instead of r17).  Since r17 by
coincidence always had the value 1, this had the effect of turning
rse_clear_invalid into a no-op.  That poses the risk of leaking kernel
state back to user-land and is hence not acceptable.

The fix below is simple, but unfortunately it costs us about 28 cycles
in syscall overhead. ;-(

Unfortunately, there isn't much we can do about that since those
registers have to be cleared one way or another.

	--david

Signed-off-by: Tony Luck <tony.luck@intel.com>
This commit is contained in:
David Mosberger-Tang 2005-04-25 13:20:38 -07:00 committed by Tony Luck
parent 93a07d0a0e
commit a37d98f6a9
1 changed files with 1 additions and 1 deletions
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2
arch/ia64/kernel/entry.S
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@ -759,7 +759,7 @@ ENTRY(ia64_leave_syscall)
(pUStk) st1 [r14]=r17
addl r3=THIS_CPU(ia64_phys_stacked_size_p8),r0
;;
(pUStk) ld4 r3=[r3] // r3 = cpu_data->phys_stacked_size_p8
(pUStk) ld4 r17=[r3] // r17 = cpu_data->phys_stacked_size_p8
mov.m ar.csd=r0 // M2 clear ar.csd
mov b6=r18 // I0 restore b6
;;