diff options
| author | Cyril Bur <cyrilbur@gmail.com> | 2016-03-16 13:29:30 +1100 |
|---|---|---|
| committer | Michael Ellerman <mpe@ellerman.id.au> | 2016-03-16 15:23:02 +1100 |
| commit | 6e669f085d595cb6053920832c89f1a13067db44 (patch) | |
| tree | abddaa4e582f0da6c0d7046b71cc1d47dc667608 | |
| parent | 2e098dcee6208a690f73e11feb29d181cae7d978 (diff) | |
powerpc: Fix unrecoverable SLB miss during restore_math()
Commit 70fe3d9 "powerpc: Restore FPU/VEC/VSX if previously used" introduces a
call to restore_math() late in the syscall return path, after MSR_RI has been
cleared. The MSR_RI flag is used to indicate whether the kernel can take
another exception or not. A cleared MSR_RI flag indicates that the kernel
cannot.
Unfortunately when a machine is under SLB pressure an SLB miss can occur
in restore_math() which (with MSR_RI cleared) leads to an unrecoverable
exception.
Unrecoverable exception 4100 at c0000000000088d8
cpu 0x0: Vector: 4100 at [c0000003fa473b20]
pc: c0000000000088d8: .load_vr_state+0x70/0x110
lr: c00000000000f710: .restore_math+0x130/0x188
sp: c0000003fa473da0
msr: 9000000002003030
current = 0xc0000007f876f180
paca = 0xc00000000fff0000 softe: 0 irq_happened: 0x01
pid = 1944, comm = K08umountfs
[link register ] c00000000000f710 .restore_math+0x130/0x188
[c0000003fa473da0] c0000003fa473e30 (unreliable)
[c0000003fa473e30] c000000000007b6c system_call+0x84/0xfc
The clearing of MSR_RI is actually an optimisation to avoid multiple MSR
writes, what must be disabled are interrupts. See comment in entry_64.S:
/*
* For performance reasons we clear RI the same time that we
* clear EE. We only need to clear RI just before we restore r13
* below, but batching it with EE saves us one expensive mtmsrd call.
* We have to be careful to restore RI if we branch anywhere from
* here (eg syscall_exit_work).
*/
At the point of calling restore_math() r13 has not been restored, as such, the
quick fix of turning MSR_RI back on for the call to restore_math() will
eliminate the occurrence of an unrecoverable exception.
We'd like to do a better fix in future.
Fixes: 70fe3d980f5f ("powerpc: Restore FPU/VEC/VSX if previously used")
Signed-off-by: Cyril Bur <cyrilbur@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
| -rw-r--r-- | arch/powerpc/kernel/entry_64.S | 9 |
1 files changed, 9 insertions, 0 deletions
diff --git a/arch/powerpc/kernel/entry_64.S b/arch/powerpc/kernel/entry_64.S index b9b125327f27..9916d150b28c 100644 --- a/arch/powerpc/kernel/entry_64.S +++ b/arch/powerpc/kernel/entry_64.S @@ -218,7 +218,16 @@ system_call: /* label this so stack traces look sane */ bne 3f #endif 2: addi r3,r1,STACK_FRAME_OVERHEAD +#ifdef CONFIG_PPC_BOOK3S + mtmsrd r10,1 /* Restore RI */ +#endif bl restore_math +#ifdef CONFIG_PPC_BOOK3S + ld r10,PACAKMSR(r13) + li r9,MSR_RI + andc r11,r10,r9 /* Re-clear RI */ + mtmsrd r11,1 +#endif ld r8,_MSR(r1) ld r3,RESULT(r1) li r11,-MAX_ERRNO |