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: 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>

diff --git a/arch/s390/kernel/asm-offsets.c b/arch/s390/kernel/asm-offsets.c
index 2012c1c..483051e 100644 (file)
--- 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();
        OFFSET(__VDSO_GETCPU_VAL, vdso_per_cpu_data, getcpu_val);
        BLANK();

diff --git a/arch/s390/kernel/entry.S b/arch/s390/kernel/entry.S
index 5346545..26bb060 100644 (file)
--- a/arch/s390/kernel/entry.S
+++ b/arch/s390/kernel/entry.S
@@ -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)