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Fix a bug in the previous change to restore the fast path for syscall

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return.  The ast() function may cause a context switch in which case
PCB_FULL_IRET would be set in the pcb.  However, the code was not
rechecking the flag after ast() returned and would not properly restore
the FSBASE and GSBASE MSRs.  To fix, recheck the PCB_FULL_IRET flag after
ast() returns.

While here, trim an instruction (and memory access) from the doreti path
and fix a typo in a comment.

MFC after:	1 week
This commit is contained in:
John Baldwin 2011-04-08 13:33:57 +00:00
parent ff265077cf
commit 13fb631aff
1 changed files with 5 additions and 6 deletions
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11
sys/amd64/amd64/exception.S
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@ -382,10 +382,10 @@ IDTVEC(fast_syscall)
FAKE_MCOUNT(TF_RIP(%rsp))
movq %rsp,%rdi
call syscall
movq PCPU(CURPCB),%rax
1: movq PCPU(CURPCB),%rax
testl $PCB_FULL_IRET,PCB_FLAGS(%rax)
jne 3f
1: /* Check for and handle AST's on return to userland. */
jnz 3f
/* Check for and handle AST's on return to userland. */
cli
movq PCPU(CURTHREAD),%rax
testl $TDF_ASTPENDING | TDF_NEEDRESCHED,TD_FLAGS(%rax)
@ -661,7 +661,7 @@ doreti:
doreti_ast:
/*
* Check for ASTs atomically with returning. Disabling CPU
* interrupts provides sufficient locking eve in the SMP case,
* interrupts provides sufficient locking even in the SMP case,
* since we will be informed of any new ASTs by an IPI.
*/
cli
@ -682,8 +682,7 @@ doreti_ast:
*/
doreti_exit:
MEXITCOUNT
movq PCPU(CURTHREAD),%r8
movq TD_PCB(%r8),%r8
movq PCPU(CURPCB),%r8
/*
* Do not reload segment registers for kernel.