[PATCH] Arm64: convert soft_restart() to assembly code

Arun Chandran
2014-08-26T13:00:01Z

On Thu, Aug 21, 2014 at 8:01 PM, Mark Rutland <mark.rutland@arm.com> wrote:
> On Thu, Aug 21, 2014 at 02:34:46PM +0100, Arun Chandran wrote:
>> Hi Mark,
>>
>> On Wed, Aug 20, 2014 at 7:46 PM, Mark Rutland <mark.rutland@arm.com> wrote:
>> > [...]
>> >
>> >> I am trying to kexec a UP-LE kernel from and SMP-LE kernel.
>> >>
>> >> > As I mentioned we do need to ensure that the CPUs are in the mode they
>> >> > started in, though I'm not sure I follow what you mean by "not waiting".
>> >> > This could be an orthogonal issue.
>> >>
>> >> If I verify the secondary CPUs from u-boot I can see that
>> >> they are all looping at
>> >>
>> >> Core number : 1
>> >> Core state : debug (AArch64 EL2)
>> >> Debug entry cause : External Debug Request
>> >> Current PC : 0x0000000000000238
>> >> Current CPSR : 0x200003c9 (EL2h)
>> >>
>> >> But after the kexec calls soft_restar(0) for all secondary CPUs
>> >> they are looping at
>> >>
>> >> Core number : 1
>> >> Core state : debug (AArch64 EL1)
>> >> Debug entry cause : External Debug Request
>> >> Current PC : 0xffffffc000083200
>> >> Current CPSR : 0x600003c5 (EL1h)
>> >>
>> >> This is what I mean by they are not waiting for
>> >> the secondary start-up address to jump.
>> >
>> > Ok.
>> >
>> >> >
>> >> > What exactly do you see, do the CPUs leave the spin-table, are they
>> >> > taking exceptions, are they getting stuck in the spin-table, etc?
>> >> >
>> >> They all are clearly resetting to address "0"(Put a breakpoint and
>> >> verified) but somehow they end up @0xffffffc000083200.
>> >> I still don't know why.
>> >>
>> >> ########
>> >> ffffffc00008319c: d503201f nop
>> >> ...
>> >> ffffffc000083200: 14000260 b ffffffc000083b80 <el1_sync>
>> >> ffffffc000083204: d503201f nop
>> >> ffffffc000083208: d503201f nop
>> >> ########
>> >
>> > That's the EL1 exception vector table.
>> >
>> > What looks to be happening is that something causes the CPUs to take an
>> > exception (at EL1). Because translation isn't enabled and the vector
>> > address doesn't map to anything, they'll take some sort of exception.
>> > Because the vectors aren't mapped that will go recursive.
>> >
>> > Your spin-table implementation might be poking something that's not
>> > accessible at EL1, in which case you require the jump to EL2 for
>> > correctness. I can't say for certain either way.
>> >
>>
>> Yes you are right I needed a jump to EL2 for putting the
>> secondary CPUs at correct spinning loop.
>
> Ok. So we need to do what I have suggested elsewhere w.r.t. jumping back
> up to EL2. As you point out below we need to synchronise with the CPUs
> on their way out too we can add a spin-table cpu_kill with a slightly
> dodgy delay to ensure that, given we have no other mechanism for
> synchronising.
>

I was able to remove the delay by pushing "set_cpu_online(cpu, false);"
further down.

############
diff --git a/arch/arm64/kernel/smp.c b/arch/arm64/kernel/smp.c
index 3fb64cb..200e49e 100644
--- a/arch/arm64/kernel/smp.c
+++ b/arch/arm64/kernel/smp.c
@@ -543,8 +543,6 @@ static void ipi_cpu_stop(unsigned int cpu)
raw_spin_unlock(&stop_lock);
}

- set_cpu_online(cpu, false);
-
local_irq_disable();

/* If we have the cpu ops use them. */
@@ -554,6 +552,8 @@ static void ipi_cpu_stop(unsigned int cpu)
&& !cpu_ops[cpu]->cpu_disable(cpu))
cpu_ops[cpu]->cpu_die(cpu);

+
+ set_cpu_online(cpu, false);
/* Otherwise spin here. */

while (1)
diff --git a/arch/arm64/kernel/smp_spin_table.c
b/arch/arm64/kernel/smp_spin_table.c
index e7275b3..8dcca88 100644
--- a/arch/arm64/kernel/smp_spin_table.c
+++ b/arch/arm64/kernel/smp_spin_table.c
@@ -149,6 +149,7 @@ static void smp_spin_table_cpu_die(unsigned int cpu)
*release_addr = 0;
__flush_dcache_area(release_addr, 8);

+ set_cpu_online(cpu, false);
mb();

soft_restart(0);
##############

This will

a) Make the waiting loop inside smp_send_stop() more meaningful

b) Make sure that at least cpu-release-addr is invalidated.

--Arun

>> I made some progress with the below changes.
>>
>> ###########
>> diff --git a/arch/arm64/kernel/head.S b/arch/arm64/kernel/head.S
>> index 607d4bb..8969922 100644
>> --- a/arch/arm64/kernel/head.S
>> +++ b/arch/arm64/kernel/head.S
>> @@ -343,6 +343,11 @@ CPU_LE( movk x0, #0x30d0, lsl #16 )
>> // Clear EE and E0E on LE systems
>> PSR_MODE_EL1h)
>> msr spsr_el2, x0
>> msr elr_el2, lr
>> + mov x0, #0x33ff
>> + movk x0, #0x801f, lsl #16
>> + msr cptr_el2, x0 // Enable traps to el2
>> when CPACR or CPACR_EL1 is accessed
>> + mov x0, #3 << 20
>> + msr cpacr_el1, x0 // Enable FP/ASIMD
>> mov w20, #BOOT_CPU_MODE_EL2 // This CPU booted in EL2
>> eret
>> ENDPROC(el2_setup)
>> diff --git a/arch/arm64/kernel/hyp-stub.S b/arch/arm64/kernel/hyp-stub.S
>> index a272f33..d8e806c 100644
>> --- a/arch/arm64/kernel/hyp-stub.S
>> +++ b/arch/arm64/kernel/hyp-stub.S
>> @@ -66,6 +66,14 @@ ENDPROC(el1_sync)
>>
>> .macro invalid_vector label
>> \label:
>> + mov x1, #0x33ff
>> + msr cptr_el2, x1 // Disable copro. traps to EL2
>> +
>> + ic ialluis
>> + isb
>> + dsb sy
>
> As far as I am aware an "isb; dsb" sequence never makes sense. It should
> be "dsb; isb". You want the I-side maintenance to complete (for which
> you have the DSB) _then_ you want to synchronise the execution context
> with the newly-visible instructions (for which you have the ISB).
>
>> +
>> + br x0
>> b \label
>> ENDPROC(\label)
>> .endm
>> diff --git a/arch/arm64/kernel/process.c b/arch/arm64/kernel/process.c
>> index 64733d4..8ca929c 100644
>> --- a/arch/arm64/kernel/process.c
>> +++ b/arch/arm64/kernel/process.c
>> @@ -65,6 +65,12 @@ void soft_restart(unsigned long addr)
>> // smp_secondary_shutdown();
>> #endif
>>
>> + /* Delay primary cpu; allow enough time for
>> + * secondaries to enter spin loop
>> + */
>> + if (smp_processor_id() == 0)
>> + mdelay(1000);
>> +
>> cpu_soft_restart(virt_to_phys(cpu_reset), addr);
>>
>> /* Should never get here */
>> diff --git a/arch/arm64/mm/proc.S b/arch/arm64/mm/proc.S
>> index 3cb6dec..f6ab468 100644
>> --- a/arch/arm64/mm/proc.S
>> +++ b/arch/arm64/mm/proc.S
>> @@ -76,6 +76,10 @@ ENTRY(cpu_reset)
>> #if defined(CONFIG_SMP)
>> /* bl secondary_shutdown */
>> #endif
>> +
>> + /* Trap to EL2 */
>> + mov x1, #3 << 20
>> + msr cpacr_el1, x1 // Enable FP/ASIMD
>> ret x0
>> ENDPROC(cpu_reset)
>>
>> @@ -200,8 +204,6 @@ ENTRY(__cpu_setup)
>> tlbi vmalle1is // invalidate I + D TLBs
>> dsb ish
>>
>> - mov x0, #3 << 20
>> - msr cpacr_el1, x0 // Enable FP/ASIMD
>> msr mdscr_el1, xzr // Reset mdscr_el1
>> /*
>> * Memory region attributes for LPAE:
>> #########
>>
>> With the above code I was able to manually kexec
>> an SMP kernel (With the help of debugger).
>>
>> Basically the branch instruction (br x0) is not working
>> in the el2 vector.
>> ------------------
>> CPU#0>h
>> Core number : 0
>> Core state : debug (AArch64 EL2)
>> Debug entry cause : External Debug Request
>> Current PC : 0x0000004000089800
>
> Does this address look similar to the VBAR_EL2, perhaps?
>
>> Current CPSR : 0x600003c9 (EL2h)
>> CPU#0>rd
>> GPR00: 00000043eb891000 0000000000000018 0000000000000006 0000000000000004
>> GPR04: 000000000000001f 000000000000001b 0000000000000000 ffffffffffffffff
>> GPR08: ffffffc3ffe80614 ffffffffffffffff 0000000000000000 0000000000000002
>> GPR12: ffffffc0000968f0 00000040008c0000 00000043eb949002 ffffffffffffffff
>> GPR16: ffffffc0000c1244 0000000000435260 0000007ff9c5d490 00000040000968c0
>> GPR20: 00000043eb891000 ffffffc3eb891000 ffffffc3eb973c00 0000000000000110
>> GPR24: ffffffc000094000 ffffffc000094cd8 000000000000008e ffffffc00082f000
>> GPR28: ffffffc3e9888000 ffffffc3e988bd00 ffffffc000095d88 00000043efb24430
>> CPU#0>go 0x00000043eb891000
>> --------------------
>>
>> I had to use the debugger to make cpu0 jump to kexec-boot code.
>> Similarly I had to manually put other CPUs to spinning code
>> using debugger. Could you please throw some light here?
>
> I really can't say. I know nothing of your platform or spin-table
> implementation, and this is nothing like what I'd expect the jump to EL2
> code to look like.
>
> Thanks,
> Mark.