[PATCH V2 1/2] powerpc/kexec: Reset secondary cpu endianess before kexec

[PATCH V2 1/2] powerpc/kexec: Reset secondary cpu endianess before kexec

[Samuel Mendoza-Jonas]

If the target kernel does not inlcude the FIXUP_ENDIAN check, coming
from a different-endian kernel will cause the target kernel to panic.
All ppc64 kernels can handle starting in big-endian mode, so return to
big-endian before branching into the target kernel.

This mainly affects pseries as secondaries on powernv are returned to
OPAL.

Signed-off-by: Samuel Mendoza-Jonas <sam.mj@au1.ibm.com>
---
v2: Add an #ifdef for subarch-specific code
    Neaten the endian check (and extra call to mfmsr!) by modifying the msr and
    branching to the target kernel in the same call to rfid.
 arch/powerpc/kernel/misc_64.S | 13 +++++++++++--
 1 file changed, 11 insertions(+), 2 deletions(-)

diff --git a/arch/powerpc/kernel/misc_64.S b/arch/powerpc/kernel/misc_64.S
index 4e314b9..89f0600 100644
--- a/arch/powerpc/kernel/misc_64.S
+++ b/arch/powerpc/kernel/misc_64.S
@@ -475,9 +475,18 @@ _GLOBAL(kexec_wait)
 #ifdef CONFIG_KEXEC		/* use no memory without kexec */
 	lwz	r4,0(r5)
 	cmpwi	0,r4,0
-	bnea	0x60
+	beq	99b
+#ifdef CONFIG_PPC_BOOK3S_64
+	li	r10,0x60
+	mfmsr	r11
+	clrrdi	r11,r11,1	/* Clear MSR_LE */
+	mtsrr0	r10
+	mtsrr1	r11
+	rfid
+#else
+	b	0x60
+#endif
 #endif
-	b	99b
 
 /* this can be in text because we won't change it until we are
  * running in real anyways
-- 
2.4.5

[PATCH V2 2/2] powerpc/kexec: Reset HILE before kexec_sequence

[Samuel Mendoza-Jonas]

On powernv secondary cpus are returned to OPAL, and will then enter the
target kernel in big-endian. However if it is set the HILE bit will persist,
causing the first exception in the target kernel to be delivered in
litte-endian regardless of the kernel endianess.
Make sure that the HILE bit is switched off before entering
kexec_sequence.

Signed-off-by: Samuel Mendoza-Jonas <sam.mj@au1.ibm.com>
---
 arch/powerpc/kernel/machine_kexec_64.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/arch/powerpc/kernel/machine_kexec_64.c b/arch/powerpc/kernel/machine_kexec_64.c
index 1a74446..2266135c 100644
--- a/arch/powerpc/kernel/machine_kexec_64.c
+++ b/arch/powerpc/kernel/machine_kexec_64.c
@@ -22,8 +22,10 @@
 #include <asm/page.h>
 #include <asm/current.h>
 #include <asm/machdep.h>
+#include <asm/opal.h>
 #include <asm/cacheflush.h>
 #include <asm/paca.h>
+#include <asm/firmware.h>
 #include <asm/mmu.h>
 #include <asm/sections.h>	/* _end */
 #include <asm/prom.h>
@@ -356,6 +358,10 @@ void default_machine_kexec(struct kimage *image)
 	 * switched to a static version!
 	 */
 
+	/* Reset HILE in case we kexec into an older BE kernel */
+	if (firmware_has_feature(FW_FEATURE_OPALv3))
+		opal_reinit_cpus(OPAL_REINIT_CPUS_HILE_BE);
+
 	/* Some things are best done in assembly.  Finding globals with
 	 * a toc is easier in C, so pass in what we can.
 	 */
-- 
2.4.5

Re: [PATCH V2 2/2] powerpc/kexec: Reset HILE before kexec_sequence

[Michael Ellerman]

On Wed, 2015-07-08 at 14:37 +1000, Samuel Mendoza-Jonas wrote:
> On powernv secondary cpus are returned to OPAL, and will then enter the
> target kernel in big-endian. However if it is set the HILE bit will persist,
> causing the first exception in the target kernel to be delivered in
> litte-endian regardless of the kernel endianess.
> Make sure that the HILE bit is switched off before entering
> kexec_sequence.
> 
> Signed-off-by: Samuel Mendoza-Jonas <sam.mj@au1.ibm.com>
> ---
>  arch/powerpc/kernel/machine_kexec_64.c | 6 ++++++
>  1 file changed, 6 insertions(+)
> 
> diff --git a/arch/powerpc/kernel/machine_kexec_64.c b/arch/powerpc/kernel/machine_kexec_64.c
> index 1a74446..2266135c 100644
> --- a/arch/powerpc/kernel/machine_kexec_64.c
> +++ b/arch/powerpc/kernel/machine_kexec_64.c
> @@ -22,8 +22,10 @@
>  #include <asm/page.h>
>  #include <asm/current.h>
>  #include <asm/machdep.h>
> +#include <asm/opal.h>
>  #include <asm/cacheflush.h>
>  #include <asm/paca.h>
> +#include <asm/firmware.h>
>  #include <asm/mmu.h>
>  #include <asm/sections.h>	/* _end */
>  #include <asm/prom.h>
> @@ -356,6 +358,10 @@ void default_machine_kexec(struct kimage *image)
>  	 * switched to a static version!
>  	 */
>  
> +	/* Reset HILE in case we kexec into an older BE kernel */
> +	if (firmware_has_feature(FW_FEATURE_OPALv3))
> +		opal_reinit_cpus(OPAL_REINIT_CPUS_HILE_BE);

It's not safe to do this here.

We are still in virtual mode and have external interrupts enabled, so you could
easily take an exception of some kind and then you'd blow up. Mashing the
keyboard during kexec might even be enough.

I think a better API would be that opal_return_cpu() deals with this under the
covers. I think we talked about that, so maybe there was some reason that
wasn't possible.

cheers

Re: [PATCH V2 2/2] powerpc/kexec: Reset HILE before kexec_sequence

[Stewart Smith]

Michael Ellerman <mpe@ellerman.id.au> writes:
> On Wed, 2015-07-08 at 14:37 +1000, Samuel Mendoza-Jonas wrote:
>> On powernv secondary cpus are returned to OPAL, and will then enter the
>> target kernel in big-endian. However if it is set the HILE bit will persist,
>> causing the first exception in the target kernel to be delivered in
>> litte-endian regardless of the kernel endianess.
>> Make sure that the HILE bit is switched off before entering
>> kexec_sequence.
>> 
>> Signed-off-by: Samuel Mendoza-Jonas <sam.mj@au1.ibm.com>
>> ---
>>  arch/powerpc/kernel/machine_kexec_64.c | 6 ++++++
>>  1 file changed, 6 insertions(+)
>> 
>> diff --git a/arch/powerpc/kernel/machine_kexec_64.c b/arch/powerpc/kernel/machine_kexec_64.c
>> index 1a74446..2266135c 100644
>> --- a/arch/powerpc/kernel/machine_kexec_64.c
>> +++ b/arch/powerpc/kernel/machine_kexec_64.c
>> @@ -22,8 +22,10 @@
>>  #include <asm/page.h>
>>  #include <asm/current.h>
>>  #include <asm/machdep.h>
>> +#include <asm/opal.h>
>>  #include <asm/cacheflush.h>
>>  #include <asm/paca.h>
>> +#include <asm/firmware.h>
>>  #include <asm/mmu.h>
>>  #include <asm/sections.h>	/* _end */
>>  #include <asm/prom.h>
>> @@ -356,6 +358,10 @@ void default_machine_kexec(struct kimage *image)
>>  	 * switched to a static version!
>>  	 */
>>  
>> +	/* Reset HILE in case we kexec into an older BE kernel */
>> +	if (firmware_has_feature(FW_FEATURE_OPALv3))
>> +		opal_reinit_cpus(OPAL_REINIT_CPUS_HILE_BE);
>
> It's not safe to do this here.
>
> We are still in virtual mode and have external interrupts enabled, so you could
> easily take an exception of some kind and then you'd blow up. Mashing the
> keyboard during kexec might even be enough.

Hrm... interrupts are disabled in kexec_sequence, should we be doing
this there instead I wonder? At this point we're pretty much at the
point of no return, so maybe we just need to disable interrupts first?

> I think a better API would be that opal_return_cpu() deals with this under the
> covers. I think we talked about that, so maybe there was some reason that
> wasn't possible.

opal_return_cpu() acts on current CPU which if we started flipping HILE
there we'd hit PowerISA 2.07 Section 2.11:
"The contents of the HILE bit must be the same for all
threads under the control of a given instance of the
hypervisor; otherwise all results are undefined."

so we'd have to do something kind of funny in opal_return_cpu() to work
out what's going on. Keeping in mind that opal_return_cpu() is also used
in the fsp code update path (which I haven't gone and really looked at
in this context though).

I'm not convinced that opal_return_cpu() doing the HILE switch is
safe when we'd be relying on the kernel to pretty much do this all at
the same time (when we really have opal_reinit_cpus to do that)

Although PowerISA also says:
"The HILE bit is set, by an implementa-
tion-dependent method, during system initialization,
and cannot be modified after system initialization."

Which... umm... we are clearly doing and have been since we started
supporting LE powernv, so there's something somewhere in some document
describing it all... I just have to find it (or poke Ben to find out
where he worked it out from).

Re: [PATCH V2 2/2] powerpc/kexec: Reset HILE before kexec_sequence

[Samuel Mendoza-Jonas]

On 08/07/15 16:51, Stewart Smith wrote:
> Michael Ellerman <mpe@ellerman.id.au> writes:
>> On Wed, 2015-07-08 at 14:37 +1000, Samuel Mendoza-Jonas wrote:
>>> On powernv secondary cpus are returned to OPAL, and will then enter the
>>> target kernel in big-endian. However if it is set the HILE bit will persist,
>>> causing the first exception in the target kernel to be delivered in
>>> litte-endian regardless of the kernel endianess.
>>> Make sure that the HILE bit is switched off before entering
>>> kexec_sequence.
>>>
>>> Signed-off-by: Samuel Mendoza-Jonas <sam.mj@au1.ibm.com>
>>> ---
>>>  arch/powerpc/kernel/machine_kexec_64.c | 6 ++++++
>>>  1 file changed, 6 insertions(+)
>>>
>>> diff --git a/arch/powerpc/kernel/machine_kexec_64.c b/arch/powerpc/kernel/machine_kexec_64.c
>>> index 1a74446..2266135c 100644
>>> --- a/arch/powerpc/kernel/machine_kexec_64.c
>>> +++ b/arch/powerpc/kernel/machine_kexec_64.c
>>> @@ -22,8 +22,10 @@
>>>  #include <asm/page.h>
>>>  #include <asm/current.h>
>>>  #include <asm/machdep.h>
>>> +#include <asm/opal.h>
>>>  #include <asm/cacheflush.h>
>>>  #include <asm/paca.h>
>>> +#include <asm/firmware.h>
>>>  #include <asm/mmu.h>
>>>  #include <asm/sections.h>	/* _end */
>>>  #include <asm/prom.h>
>>> @@ -356,6 +358,10 @@ void default_machine_kexec(struct kimage *image)
>>>  	 * switched to a static version!
>>>  	 */
>>>  
>>> +	/* Reset HILE in case we kexec into an older BE kernel */
>>> +	if (firmware_has_feature(FW_FEATURE_OPALv3))
>>> +		opal_reinit_cpus(OPAL_REINIT_CPUS_HILE_BE);
>>
>> It's not safe to do this here.
>>
>> We are still in virtual mode and have external interrupts enabled, so you could
>> easily take an exception of some kind and then you'd blow up. Mashing the
>> keyboard during kexec might even be enough.
> 
> Hrm... interrupts are disabled in kexec_sequence, should we be doing
> this there instead I wonder? At this point we're pretty much at the
> point of no return, so maybe we just need to disable interrupts first?
> 
>> I think a better API would be that opal_return_cpu() deals with this under the
>> covers. I think we talked about that, so maybe there was some reason that
>> wasn't possible.
> 
> opal_return_cpu() acts on current CPU which if we started flipping HILE
> there we'd hit PowerISA 2.07 Section 2.11:
> "The contents of the HILE bit must be the same for all
> threads under the control of a given instance of the
> hypervisor; otherwise all results are undefined."
> 
> so we'd have to do something kind of funny in opal_return_cpu() to work
> out what's going on. Keeping in mind that opal_return_cpu() is also used
> in the fsp code update path (which I haven't gone and really looked at
> in this context though).
> 
> I'm not convinced that opal_return_cpu() doing the HILE switch is
> safe when we'd be relying on the kernel to pretty much do this all at
> the same time (when we really have opal_reinit_cpus to do that)

Having discovered opal_call_realmode, it looks like we can probably do this
safely in real mode just before moving the kernel around and releasing
the secondaries into the next kernel. I'll test this and send a V2 if it
looks good.

> 
> Although PowerISA also says:
> "The HILE bit is set, by an implementa-
> tion-dependent method, during system initialization,
> and cannot be modified after system initialization."
> 
> Which... umm... we are clearly doing and have been since we started
> supporting LE powernv, so there's something somewhere in some document
> describing it all... I just have to find it (or poke Ben to find out
> where he worked it out from).
> 


-- 
-----------
LTC Ozlabs
IBM

Re: [PATCH V2 2/2] powerpc/kexec: Reset HILE before kexec_sequence

[Michael Ellerman]

On Wed, 2015-07-08 at 16:51 +1000, Stewart Smith wrote:
> Michael Ellerman <mpe@ellerman.id.au> writes:
> > On Wed, 2015-07-08 at 14:37 +1000, Samuel Mendoza-Jonas wrote:
> >> On powernv secondary cpus are returned to OPAL, and will then enter the
> >> target kernel in big-endian. However if it is set the HILE bit will persist,
> >> causing the first exception in the target kernel to be delivered in
> >> litte-endian regardless of the kernel endianess.
> >> Make sure that the HILE bit is switched off before entering
> >> kexec_sequence.
> >> 
> >> Signed-off-by: Samuel Mendoza-Jonas <sam.mj@au1.ibm.com>
> >> ---
> >>  arch/powerpc/kernel/machine_kexec_64.c | 6 ++++++
> >>  1 file changed, 6 insertions(+)
> >> 
> >> diff --git a/arch/powerpc/kernel/machine_kexec_64.c b/arch/powerpc/kernel/machine_kexec_64.c
> >> index 1a74446..2266135c 100644
> >> --- a/arch/powerpc/kernel/machine_kexec_64.c
> >> +++ b/arch/powerpc/kernel/machine_kexec_64.c
> >> @@ -356,6 +358,10 @@ void default_machine_kexec(struct kimage *image)
> >>  	 * switched to a static version!
> >>  	 */
> >>  
> >> +	/* Reset HILE in case we kexec into an older BE kernel */
> >> +	if (firmware_has_feature(FW_FEATURE_OPALv3))
> >> +		opal_reinit_cpus(OPAL_REINIT_CPUS_HILE_BE);
> >
> > It's not safe to do this here.
> >
> > We are still in virtual mode and have external interrupts enabled, so you could
> > easily take an exception of some kind and then you'd blow up. Mashing the
> > keyboard during kexec might even be enough.
> 
> Hrm... interrupts are disabled in kexec_sequence, should we be doing
> this there instead I wonder? At this point we're pretty much at the
> point of no return, so maybe we just need to disable interrupts first?
> 
> > I think a better API would be that opal_return_cpu() deals with this under the
> > covers. I think we talked about that, so maybe there was some reason that
> > wasn't possible.
> 
> opal_return_cpu() acts on current CPU which if we started flipping HILE
> there we'd hit PowerISA 2.07 Section 2.11:
> "The contents of the HILE bit must be the same for all
> threads under the control of a given instance of the
> hypervisor; otherwise all results are undefined."
> 
> so we'd have to do something kind of funny in opal_return_cpu() to work
> out what's going on. Keeping in mind that opal_return_cpu() is also used
> in the fsp code update path (which I haven't gone and really looked at
> in this context though).
> 
> I'm not convinced that opal_return_cpu() doing the HILE switch is
> safe when we'd be relying on the kernel to pretty much do this all at
> the same time (when we really have opal_reinit_cpus to do that)

Yeah I agree.

What I meant is that after you return a cpu to OPAL, when you (or actually
someone else) restart it, at that point it should be put into a well defined
state, including HILE.

cheers

Re: [PATCH V2 2/2] powerpc/kexec: Reset HILE before kexec_sequence

[Stewart Smith]

Michael Ellerman <mpe@ellerman.id.au> writes:
>> > I think a better API would be that opal_return_cpu() deals with this under the
>> > covers. I think we talked about that, so maybe there was some reason that
>> > wasn't possible.
>> 
>> opal_return_cpu() acts on current CPU which if we started flipping HILE
>> there we'd hit PowerISA 2.07 Section 2.11:
>> "The contents of the HILE bit must be the same for all
>> threads under the control of a given instance of the
>> hypervisor; otherwise all results are undefined."
>> 
>> so we'd have to do something kind of funny in opal_return_cpu() to work
>> out what's going on. Keeping in mind that opal_return_cpu() is also used
>> in the fsp code update path (which I haven't gone and really looked at
>> in this context though).
>> 
>> I'm not convinced that opal_return_cpu() doing the HILE switch is
>> safe when we'd be relying on the kernel to pretty much do this all at
>> the same time (when we really have opal_reinit_cpus to do that)
>
> Yeah I agree.
>
> What I meant is that after you return a cpu to OPAL, when you (or actually
> someone else) restart it, at that point it should be put into a well defined
> state, including HILE.

I'll go and try and investigate exactly what's going on here with the
hardware, it's possible some of the hardware documentation is Anton
Blanchard and that needs to make it into documents rather than just
skiboot source. Especially around what makes sense for all-at-a-time
(reinit_cpu with HILE switch) versus one at a time (start
cpu/return_cpu).

Of course, that's a skiboot problem rather than a Linux one.

I think Sam is looking at doing the opal call in real mode somewhere in
kexec_sequence just before we jump into the new kernel. This should make
it so that everything works on existing OPAL APIs, while at the same
time we can go and check if there's a sensible/valid way we can deal
with the hardware to get a broader well defined state after certain
calls.

I'm in favor of using existing calls rather than making a firmware
upgrade a requirement though.

Re: [PATCH V2 1/2] powerpc/kexec: Reset secondary cpu endianess before kexec

[Scott Wood]

On Wed, 2015-07-08 at 14:37 +1000, Samuel Mendoza-Jonas wrote:
> If the target kernel does not inlcude the FIXUP_ENDIAN check, coming
> from a different-endian kernel will cause the target kernel to panic.
> All ppc64 kernels can handle starting in big-endian mode, so return to
> big-endian before branching into the target kernel.
> 
> This mainly affects pseries as secondaries on powernv are returned to
> OPAL.
> 
> Signed-off-by: Samuel Mendoza-Jonas <sam.mj@au1.ibm.com>
> ---
> v2: Add an #ifdef for subarch-specific code
>     Neaten the endian check (and extra call to mfmsr!) by modifying the msr 
> and
>     branching to the target kernel in the same call to rfid.
>  arch/powerpc/kernel/misc_64.S | 13 +++++++++++--
>  1 file changed, 11 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/powerpc/kernel/misc_64.S b/arch/powerpc/kernel/misc_64.S
> index 4e314b9..89f0600 100644
> --- a/arch/powerpc/kernel/misc_64.S
> +++ b/arch/powerpc/kernel/misc_64.S
> @@ -475,9 +475,18 @@ _GLOBAL(kexec_wait)
>  #ifdef CONFIG_KEXEC          /* use no memory without kexec */
>       lwz     r4,0(r5)
>       cmpwi   0,r4,0
> -     bnea    0x60
> +     beq     99b
> +#ifdef CONFIG_PPC_BOOK3S_64
> +     li      r10,0x60
> +     mfmsr   r11
> +     clrrdi  r11,r11,1       /* Clear MSR_LE */
> +     mtsrr0  r10
> +     mtsrr1  r11
> +     rfid
> +#else
> +     b       0x60
> +#endif
>  #endif
> -     b       99b

"b 0x60" needs to be "ba 0x60".

-Scott