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

Arun Chandran
2014-08-20T13:57:09Z

On Wed, Aug 20, 2014 at 4:24 PM, Mark Rutland <mark.rutland@arm.com> wrote:
> On Wed, Aug 20, 2014 at 11:28:52AM +0100, Arun Chandran wrote:
>> Hi Mark,
>
> Hi Arun,
>
>> On Fri, Aug 15, 2014 at 11:51 PM, Mark Rutland <mark.rutland@arm.com> wrote:
>> > Hi Geoff,
>> >
>> > On Fri, Aug 15, 2014 at 06:20:21PM +0100, Geoff Levand wrote:
>> >> Hi Arun,
>> >>
>> >> On Tue, 2014-08-12 at 18:12 +0530, Arun Chandran wrote:
>> >> > soft_restart() will fail on arm64 systems that does not
>> >> > quarantee the flushing of cache to PoC with flush_cache_all().
>> >> >
>> >> > soft_restart(addr)
>> >> > {
>> >> > push_to_stack(addr);
>> >> >
>> >> > Do mm setup for restart;
>> >> > Flush&turnoff D-cache;
>> >> >
>> >> > pop_from_stack(addr); --> fails here as addr is not at PoC
>> >> > cpu_reset(addr) --> Jumps to invalid address
>> >> > }
>> >>
>> >> For the cpu-ops shutdown I'm working on I need a call to move the
>> >> secondary processors to an identity mapped spin loop after the identity
>> >> map is enabled. I want to do this in C code, so it needs to happen
>> >> after the identity map is enabled, and before the dcache is disabled.
>> >>
>> >> I think to do this we can keep the existing soft_restart(addr) routine
>> >> with something like this:
>> >>
>> >> void soft_restart(unsigned long addr)
>> >> {
>> >> setup_mm_for_reboot();
>> >>
>> >> #if defined(CONFIG_SMP)
>> >> smp_secondary_shutdown();
>> >> #endif
>> >>
>> >> cpu_soft_restart(addr);
>> >>
>> >> /* Should never get here */
>> >> BUG();
>> >> }
>> >>
>> >
>> > I don't follow why you need a hook in the middle of soft_restart. That
>> > sounds like a layering violation to me.
>> >
>> > I assume this is for implementing the spin-table cpu-return-addr idea?
>> >
>> > If so, what's wrong with something like:
>> >
>> > #define ADDR_INVALID ((unsigned long)-1)
>> > static DEFINE_PER_CPU(unsigned long, return_addr) = ADDR_INVALID;
>> >
>> > int spin_table_cpu_disable(unsigned int cpu)
>> > {
>> > if (per_cpu(return_addr, cpu) != ADDR_INVALID)
>> > return 0;
>> >
>> > return -EOPNOTSUPP;
>> > }
>> >
>> > void spin_table_cpu_die(unsigned int cpu)
>> > {
>> > unsigned long release_addr = per_cpu(return_addr, cpu);
>> >
>> > /*
>> > * We should have a local_disable(DBG|ASYNC|FIQ|IRQ) function or
>> > * something similar as these are all context synchronising and
>> > * therefore expensive.
>> > */
>> > local_dbg_disable();
>> > local_async_disable();
>> > local_fiq_disable();
>> > arch_local_irq_disable();
>> >
>> > soft_restart(release_addr);
>> > }
>> >
>>
>> I am trying the above method for kexec.
>>
>> As of now I have hardcoded cpu-return-addr , which is 0x0 in my
>> case.
>>
>> ##################
>> diff --git a/arch/arm64/kernel/smp_spin_table.c
>> b/arch/arm64/kernel/smp_spin_table.c
>> index e54ceed..e7275b3 100644
>> --- a/arch/arm64/kernel/smp_spin_table.c
>> +++ b/arch/arm64/kernel/smp_spin_table.c
>> @@ -27,6 +27,7 @@
>> #include <asm/cpu_ops.h>
>> #include <asm/cputype.h>
>> #include <asm/smp_plat.h>
>> +#include <asm/system_misc.h>
>>
>> #include "cpu-properties.h"
>>
>> @@ -97,7 +98,7 @@ static int smp_spin_table_cpu_prepare(unsigned int cpu)
>> * boot-loader's endianess before jumping. This is mandated by
>> * the boot protocol.
>> */
>> - writeq_relaxed(__pa(secondary_holding_entry), release_addr);
>> + writeq_relaxed(__pa(secondary_holding_pen), release_addr);
>> __flush_dcache_area((__force void *)release_addr,
>> sizeof(*release_addr));
>>
>> @@ -135,18 +136,22 @@ static void smp_spin_table_cpu_die(unsigned int cpu)
>> {
>> u64 *release_addr = phys_to_virt(cpu_release_addr[cpu]);
>>
>> - pr_devel("%s:%d: id: %u, holding count: %lu\n", __func__, __LINE__,
>> - smp_processor_id(), secondary_holding_pen_count);
>> + pr_devel("%s:%d: id: %u dying\n", __func__, __LINE__,
>> + smp_processor_id());
>>
>> /* Send cpu back to secondary_holding_pen. */
>>
>> + local_dbg_disable(); // FIXME: need this???
>> + local_async_disable(); // FIXME: need this???
>> local_fiq_disable(); // FIXME: need this???
>> + arch_local_irq_disable();
>>
>> *release_addr = 0;
>> + __flush_dcache_area(release_addr, 8);
>>
>> mb();
>>
>> - secondary_holding_pen();
>> + soft_restart(0);
>>
>> BUG();
>> }
>> ###########################
>>
>> I can see that my secondary cpu's are not going to the exact same
>> state as they were in when I boot a SMP kernel from u-boot.
>>
>> [[They are not waiting for addr(secondary_holding_pen()) at
>> release_addr]]
>>
>> Like geoff mentioned in another mail do we need to
>> to get back to EL2 before re-entering the bootwrapper program?
>

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.

>
> 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
########

> Are the cpu-release-addr entries getting restored to zero before each
> CPU begins polling them?

Yes I can see

CPU#1>md 0x400000fff8
40_0000fff8 : 00000000

--Arun