powerpc/64s: return more carefully from sreset NMI
Nicholas Piggin
reviewerPATCH 1/1 powerpc/64s: return more carefully from sreset NMI
System Reset, being an NMI, must return more carefully than other interrupts. It has traditionally returned via the nromal return from exception path, but that has a number of problems.
- r13 does not get restored if returning to kernel. This is for interrupts which may cause a context switch, which sreset will never do. Interrupting OPAL (which uses a different r13) is one place where this causes breakage.
- It may cause several other problems returning to kernel with preempt or TIF_EMULATE_STACK_STORE if it hits at the wrong time.
It's safer just to have a simple restore and return, like machine check which is the other NMI.
--- arch/powerpc/kernel/exceptions-64s.S | 61 ++++++++++++++++++++++++++++++++++-- 1 file changed, 58 insertions(+), 3 deletions(-)
arch/powerpc/kernel/exceptions-64s.S +58 -3
@@ -139,6 +139,21 @@ EXC_COMMON_BEGIN(system_reset_idle_common) b pnv_powersave_wakeup #endif +/* + * Set IRQS_ALL_DISABLED unconditionally so arch_irqs_disabled does + * the right thing. We do not want to reconcile because that goes + * through irq tracing which we don't want in NMI. + * + * Save PACAIRQHAPPENED because some code will do a hard disable + * (e.g., xmon). So we want to restore this back to where it was + * when we return. DAR is unused in the stack, so save it there. + */ +#define ADD_RECONCILE_NMI \ + li r10,IRQS_ALL_DISABLED; \ + stb r10,PACAIRQSOFTMASK(r13); \ + lbz r10,PACAIRQHAPPENED(r13); \ + std r10,_DAR(r1) + EXC_COMMON_BEGIN(system_reset_common) /* * Increment paca->in_nmi then enable MSR_RI. SLB or MCE will be able
@@ -157,16 +172,56 @@ EXC_COMMON_BEGIN(system_reset_common) subi r1,r1,INT_FRAME_SIZE EXCEPTION_COMMON_NORET_STACK(PACA_EXNMI, 0x100, system_reset, system_reset_exception, - ADD_NVGPRS;ADD_RECONCILE) + ADD_NVGPRS;ADD_RECONCILE_NMI) + + /* This (and MCE) can be simplified with mtmsrd L=1 */ + /* Clear MSR_RI before setting SRR0 and SRR1. */ + li r0,MSR_RI + mfmsr r9 + andc r9,r9,r0 + mtmsrd r9,1 /* - * The stack is no longer in use, decrement in_nmi. + * MSR_RI is clear, now we can decrement paca->in_nmi. */ lhz r10,PACA_IN_NMI(r13) subi r10,r10,1 sth r10,PACA_IN_NMI(r13) - b ret_from_except + /* + * Restore soft mask settings. + */ + ld r10,_DAR(r1) + stb r10,PACAIRQHAPPENED(r13) + ld r10,SOFTE(r1) + stb r10,PACAIRQSOFTMASK(r13) + + /* + * Keep below code in synch with MACHINE_CHECK_HANDLER_WINDUP. + * Should share common bits... + */ + + /* Move original SRR0 and SRR1 into the respective regs */ + ld r9,_MSR(r1) + mtspr SPRN_SRR1,r9 + ld r3,_NIP(r1) + mtspr SPRN_SRR0,r3 + ld r9,_CTR(r1) + mtctr r9 + ld r9,_XER(r1) + mtxer r9 + ld r9,_LINK(r1) + mtlr r9 + REST_GPR(0, r1) + REST_8GPRS(2, r1) + REST_GPR(10, r1) + ld r11,_CCR(r1) + mtcr r11 + REST_GPR(11, r1) + REST_2GPRS(12, r1) + /* restore original r1. */ + ld r1,GPR1(r1) + RFI_TO_USER_OR_KERNEL #ifdef CONFIG_PPC_PSERIES /*
Signature · 1 line
2.16.1
Michael Ellerman
AppliedQuoted 9 lines · Nicholas Piggin
System Reset, being an NMI, must return more carefully than other interrupts. It has traditionally returned via the nromal return from exception path, but that has a number of problems.
- r13 does not get restored if returning to kernel. This is for interrupts which may cause a context switch, which sreset will never do. Interrupting OPAL (which uses a different r13) is one place where this causes breakage.
Quoted 7 lines
- It may cause several other problems returning to kernel with preempt or
TIF_EMULATE_STACK_STOREif it hits at the wrong time.It's safer just to have a simple restore and return, like machine check which is the other NMI.
Signed-off-by Nicholas Piggin <[email protected]>
Applied to powerpc next, thanks.
https://git.kernel.org/powerpc/c/15b4dd7981496f51c5f9262a5e0761
cheers