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s390: fix fpu restore in entry.S 

We need to disable interrupts in load_fpu_regs(). Otherwise an
interrupt might come in after the registers are loaded, but before
CIF_FPU is cleared in load_fpu_regs(). When the interrupt returns,
CIF_FPU will be cleared and the registers will never be restored.

The entry.S code usually saves the interrupt state in __SF_EMPTY on the
stack when disabling/restoring interrupts. sie64a however saves the pointer
to the sie control block in __SF_SIE_CONTROL, which references the same
location.  This is non-obvious to the reader. To avoid thrashing the sie
control block pointer in load_fpu_regs(), move the __SIE_* offsets eight
bytes after __SF_EMPTY on the stack.

Cc: <stable@vger.kernel.org> # 5.8
Fixes: 0b0ed657fe ("s390: remove critical section cleanup from entry.S")
Reported-by: Pierre Morel <pmorel@linux.ibm.com>
Signed-off-by: Sven Schnelle <svens@linux.ibm.com>
Acked-by: Christian Borntraeger <borntraeger@de.ibm.com>
Reviewed-by: Heiko Carstens <hca@linux.ibm.com>
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>
This commit is contained in:
Sven Schnelle 2020-11-20 14:17:52 +01:00 committed by Heiko Carstens
parent 78d732e1f3
commit 1179f170b6
2 changed files with 7 additions and 5 deletions
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10
arch/s390/kernel/asm-offsets.c
View File

@ -53,11 +53,11 @@ int main(void)
/* stack_frame offsets */
OFFSET(__SF_BACKCHAIN, stack_frame, back_chain);
OFFSET(__SF_GPRS, stack_frame, gprs);
OFFSET(__SF_EMPTY, stack_frame, empty1);
OFFSET(__SF_SIE_CONTROL, stack_frame, empty1[0]);
OFFSET(__SF_SIE_SAVEAREA, stack_frame, empty1[1]);
OFFSET(__SF_SIE_REASON, stack_frame, empty1[2]);
OFFSET(__SF_SIE_FLAGS, stack_frame, empty1[3]);
OFFSET(__SF_EMPTY, stack_frame, empty1[0]);
OFFSET(__SF_SIE_CONTROL, stack_frame, empty1[1]);
OFFSET(__SF_SIE_SAVEAREA, stack_frame, empty1[2]);
OFFSET(__SF_SIE_REASON, stack_frame, empty1[3]);
OFFSET(__SF_SIE_FLAGS, stack_frame, empty1[4]);
BLANK();
OFFSET(__VDSO_GETCPU_VAL, vdso_per_cpu_data, getcpu_val);
BLANK();

2
arch/s390/kernel/entry.S
View File

@ -1068,6 +1068,7 @@ EXPORT_SYMBOL(save_fpu_regs)
* %r4
*/
load_fpu_regs:
stnsm __SF_EMPTY(%r15),0xfc
lg %r4,__LC_CURRENT
aghi %r4,__TASK_thread
TSTMSK __LC_CPU_FLAGS,_CIF_FPU
@ -1099,6 +1100,7 @@ load_fpu_regs:
.Lload_fpu_regs_done:
ni __LC_CPU_FLAGS+7,255-_CIF_FPU
.Lload_fpu_regs_exit:
ssm __SF_EMPTY(%r15)
BR_EX %r14
.Lload_fpu_regs_end:
ENDPROC(load_fpu_regs)