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Subject[PATCH 5.9 014/152] s390: fix fpu restore in entry.S
Date
From: Sven Schnelle <svens@linux.ibm.com>

commit 1179f170b6f0af7bb0b3b7628136eaac450ddf31 upstream.

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: 0b0ed657fe00 ("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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
arch/s390/kernel/asm-offsets.c | 10 +++++-----
arch/s390/kernel/entry.S | 2 ++
2 files changed, 7 insertions(+), 5 deletions(-)

--- a/arch/s390/kernel/asm-offsets.c
+++ b/arch/s390/kernel/asm-offsets.c
@@ -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();
/* timeval/timezone offsets for use by vdso */
OFFSET(__VDSO_UPD_COUNT, vdso_data, tb_update_count);
--- a/arch/s390/kernel/entry.S
+++ b/arch/s390/kernel/entry.S
@@ -1072,6 +1072,7 @@ 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
@@ -1103,6 +1104,7 @@ 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)

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