Excerpts from Nicholas Piggin's message of April 1, 2021 5:36 pm:
> Excerpts from Andreas Schwab's message of March 30, 2021 2:23 am:
>> On Mär 29 2021, Andreas Schwab wrote:
>>
>>> On Mär 29 2021, Michael Ellerman wrote:
>>>
>>>> Nicholas Piggin <npig...@gmail.com> writes:
>>>>> There is no need for this to be in asm, use the new intrrupt entry
>>>>> wrapper.
>>>>>
>>>>> Signed-off-by: Nicholas Piggin <npig...@gmail.com>
>>>>> ---
>>>>> Hopefully this works on a real G5 now, but I couldn't reproduce the
>>>>> problem with QEMU.
>>>>
>>>> It still prevents my G5 from booting.
>>>
>>> I see differing failures. What's common is that there is a pause of
>>> about 60 seconds before the crash occurs. It looks like the crash
>>> occurs in power4_idle_nap+0x30/0x34. Unfortuately, the BootX console is
>>> too small to see enough.
>>
>> I was now able to see the messages on the VGA console, and the problem
>> is actually that the cpus are starting to stall.
>
> This is strange, I haven't been able to figure out what is wrong.
>
> I've been looking at QEMU code and now I'll have to try find a POWER4/5
> or PPC970 manual to see what exactly this MSR[POW] thing does and make
> sure QEMU matches it.
I worked it out. There was a window where it could take another
interrupt before the first one adjusts the nip.
I managed to trigger it in qemu and this version fixed it.
---
arch/powerpc/include/asm/interrupt.h | 24 ++++++++++++++
arch/powerpc/include/asm/processor.h | 1 +
arch/powerpc/include/asm/thread_info.h | 6 ++++
arch/powerpc/kernel/exceptions-64s.S | 45 --------------------------
arch/powerpc/kernel/idle_book3s.S | 4 +++
5 files changed, 35 insertions(+), 45 deletions(-)
diff --git a/arch/powerpc/include/asm/interrupt.h
b/arch/powerpc/include/asm/interrupt.h
index e8d09a841373..2643028cf67a 100644
--- a/arch/powerpc/include/asm/interrupt.h
+++ b/arch/powerpc/include/asm/interrupt.h
@@ -9,6 +9,17 @@
#include <asm/kprobes.h>
#include <asm/runlatch.h>
+static inline void nap_adjust_return(struct pt_regs *regs)
+{
+#ifdef CONFIG_PPC_970_NAP
+ if (unlikely(test_thread_local_flags(_TLF_NAPPING))) {
+ /* Can avoid a test-and-clear because NMIs do not call this */
+ clear_thread_local_flags(_TLF_NAPPING);
+ regs->nip = (unsigned long)power4_idle_nap_return;
+ }
+#endif
+}
+
struct interrupt_state {
#ifdef CONFIG_PPC_BOOK3E_64
enum ctx_state ctx_state;
@@ -109,6 +120,14 @@ static inline void interrupt_async_enter_prepare(struct
pt_regs *regs, struct in
static inline void interrupt_async_exit_prepare(struct pt_regs *regs, struct
interrupt_state *state)
{
+ /*
+ * Adjust at exit so the main handler sees the true NIA. This must
+ * come before irq_exit() because irq_exit can enable interrupts, and
+ * if another interrupt is taken before nap_adjust_return has run
+ * here, then that interrupt would return directly to idle nap return.
+ */
+ nap_adjust_return(regs);
+
irq_exit();
interrupt_exit_prepare(regs, state);
}
@@ -164,6 +183,11 @@ static inline void interrupt_nmi_exit_prepare(struct
pt_regs *regs, struct inter
radix_enabled() || (mfmsr() & MSR_DR))
nmi_exit();
+ /*
+ * nmi does not call nap_adjust_return because nmi should not create
+ * new work to do (must use irq_work for that).
+ */
+
#ifdef CONFIG_PPC64
if (TRAP(regs) != 0x900 && TRAP(regs) != 0xf00 && TRAP(regs) != 0x260)
this_cpu_set_ftrace_enabled(state->ftrace_enabled);
diff --git a/arch/powerpc/include/asm/processor.h
b/arch/powerpc/include/asm/processor.h
index 8acc3590c971..eedc3c775141 100644
--- a/arch/powerpc/include/asm/processor.h
+++ b/arch/powerpc/include/asm/processor.h
@@ -393,6 +393,7 @@ extern unsigned long isa300_idle_stop_mayloss(unsigned long
psscr_val);
extern unsigned long isa206_idle_insn_mayloss(unsigned long type);
#ifdef CONFIG_PPC_970_NAP
extern void power4_idle_nap(void);
+void power4_idle_nap_return(void);
#endif
extern unsigned long cpuidle_disable;
diff --git a/arch/powerpc/include/asm/thread_info.h
b/arch/powerpc/include/asm/thread_info.h
index 386d576673a1..bf137151100b 100644
--- a/arch/powerpc/include/asm/thread_info.h
+++ b/arch/powerpc/include/asm/thread_info.h
@@ -152,6 +152,12 @@ void arch_setup_new_exec(void);
#ifndef __ASSEMBLY__
+static inline void clear_thread_local_flags(unsigned int flags)
+{
+ struct thread_info *ti = current_thread_info();
+ ti->local_flags &= ~flags;
+}
+
static inline bool test_thread_local_flags(unsigned int flags)
{
struct thread_info *ti = current_thread_info();
diff --git a/arch/powerpc/kernel/exceptions-64s.S
b/arch/powerpc/kernel/exceptions-64s.S
index 8082b690e874..0cdb59e8b577 100644
--- a/arch/powerpc/kernel/exceptions-64s.S
+++ b/arch/powerpc/kernel/exceptions-64s.S
@@ -692,25 +692,6 @@ END_FTR_SECTION_IFSET(CPU_FTR_CFAR)
ld r1,GPR1(r1)
.endm
-/*
- * When the idle code in power4_idle puts the CPU into NAP mode,
- * it has to do so in a loop, and relies on the external interrupt
- * and decrementer interrupt entry code to get it out of the loop.
- * It sets the _TLF_NAPPING bit in current_thread_info()->local_flags
- * to signal that it is in the loop and needs help to get out.
- */
-#ifdef CONFIG_PPC_970_NAP
-#define FINISH_NAP \
-BEGIN_FTR_SECTION \
- ld r11, PACA_THREAD_INFO(r13); \
- ld r9,TI_LOCAL_FLAGS(r11); \
- andi. r10,r9,_TLF_NAPPING; \
- bnel power4_fixup_nap; \
-END_FTR_SECTION_IFSET(CPU_FTR_CAN_NAP)
-#else
-#define FINISH_NAP
-#endif
-
/*
* There are a few constraints to be concerned with.
* - Real mode exceptions code/data must be located at their physical location.
@@ -1248,7 +1229,6 @@ EXC_COMMON_BEGIN(machine_check_common)
*/
GEN_COMMON machine_check
- FINISH_NAP
/* Enable MSR_RI when finished with PACA_EXMC */
li r10,MSR_RI
mtmsrd r10,1
@@ -1571,7 +1551,6 @@ EXC_VIRT_BEGIN(hardware_interrupt, 0x4500, 0x100)
EXC_VIRT_END(hardware_interrupt, 0x4500, 0x100)
EXC_COMMON_BEGIN(hardware_interrupt_common)
GEN_COMMON hardware_interrupt
- FINISH_NAP
addi r3,r1,STACK_FRAME_OVERHEAD
bl do_IRQ
b interrupt_return
@@ -1801,7 +1780,6 @@ EXC_VIRT_BEGIN(decrementer, 0x4900, 0x80)
EXC_VIRT_END(decrementer, 0x4900, 0x80)
EXC_COMMON_BEGIN(decrementer_common)
GEN_COMMON decrementer
- FINISH_NAP
addi r3,r1,STACK_FRAME_OVERHEAD
bl timer_interrupt
b interrupt_return
@@ -1886,7 +1864,6 @@ EXC_VIRT_BEGIN(doorbell_super, 0x4a00, 0x100)
EXC_VIRT_END(doorbell_super, 0x4a00, 0x100)
EXC_COMMON_BEGIN(doorbell_super_common)
GEN_COMMON doorbell_super
- FINISH_NAP
addi r3,r1,STACK_FRAME_OVERHEAD
#ifdef CONFIG_PPC_DOORBELL
bl doorbell_exception
@@ -2237,7 +2214,6 @@ EXC_COMMON_BEGIN(hmi_exception_early_common)
EXC_COMMON_BEGIN(hmi_exception_common)
GEN_COMMON hmi_exception
- FINISH_NAP
addi r3,r1,STACK_FRAME_OVERHEAD
bl handle_hmi_exception
b interrupt_return
@@ -2266,7 +2242,6 @@ EXC_VIRT_BEGIN(h_doorbell, 0x4e80, 0x20)
EXC_VIRT_END(h_doorbell, 0x4e80, 0x20)
EXC_COMMON_BEGIN(h_doorbell_common)
GEN_COMMON h_doorbell
- FINISH_NAP
addi r3,r1,STACK_FRAME_OVERHEAD
#ifdef CONFIG_PPC_DOORBELL
bl doorbell_exception
@@ -2299,7 +2274,6 @@ EXC_VIRT_BEGIN(h_virt_irq, 0x4ea0, 0x20)
EXC_VIRT_END(h_virt_irq, 0x4ea0, 0x20)
EXC_COMMON_BEGIN(h_virt_irq_common)
GEN_COMMON h_virt_irq
- FINISH_NAP
addi r3,r1,STACK_FRAME_OVERHEAD
bl do_IRQ
b interrupt_return
@@ -2345,7 +2319,6 @@ EXC_VIRT_BEGIN(performance_monitor, 0x4f00, 0x20)
EXC_VIRT_END(performance_monitor, 0x4f00, 0x20)
EXC_COMMON_BEGIN(performance_monitor_common)
GEN_COMMON performance_monitor
- FINISH_NAP
addi r3,r1,STACK_FRAME_OVERHEAD
bl performance_monitor_exception
b interrupt_return
@@ -3096,24 +3069,6 @@ USE_FIXED_SECTION(virt_trampolines)
__end_interrupts:
DEFINE_FIXED_SYMBOL(__end_interrupts)
-#ifdef CONFIG_PPC_970_NAP
- /*
- * Called by exception entry code if _TLF_NAPPING was set, this clears
- * the NAPPING flag, and redirects the exception exit to
- * power4_fixup_nap_return.
- */
- .globl power4_fixup_nap
-EXC_COMMON_BEGIN(power4_fixup_nap)
- andc r9,r9,r10
- std r9,TI_LOCAL_FLAGS(r11)
- LOAD_REG_ADDR(r10, power4_idle_nap_return)
- std r10,_NIP(r1)
- blr
-
-power4_idle_nap_return:
- blr
-#endif
-
CLOSE_FIXED_SECTION(real_vectors);
CLOSE_FIXED_SECTION(real_trampolines);
CLOSE_FIXED_SECTION(virt_vectors);
diff --git a/arch/powerpc/kernel/idle_book3s.S
b/arch/powerpc/kernel/idle_book3s.S
index f9e6d83e6720..abb719b21cae 100644
--- a/arch/powerpc/kernel/idle_book3s.S
+++ b/arch/powerpc/kernel/idle_book3s.S
@@ -209,4 +209,8 @@ _GLOBAL(power4_idle_nap)
mtmsrd r7
isync
b 1b
+
+ .globl power4_idle_nap_return
+power4_idle_nap_return:
+ blr
#endif
--
2.23.0
