undefined instruction d5380001

undefined instruction d5380001

[Matwey V. Kornilov]

Hello,

I am running 4.13.3 on rockchip 3328 platform(aarch64) with glibc 2.26
and see the following at booting:

[   11.152061] modprobe[93]: undefined instruction: pc=0000ffff8ca48ff4
[   11.152707] Code: d503201f 8a180320 92750001 365ffc20 (d5380001)
[   11.154347] modprobe[94]: undefined instruction: pc=0000ffff94243ff4
[   11.154991] Code: d503201f 8a180320 92750001 365ffc20 (d5380001)
[   11.157070] modprobe[97]: undefined instruction: pc=0000ffff839a0ff4
[   11.157715] Code: d503201f 8a180320 92750001 365ffc20 (d5380001)
[   11.159265] modprobe[98]: undefined instruction: pc=0000ffffb0591ff4
[   11.159908] Code: d503201f 8a180320 92750001 365ffc20 (d5380001)

As far as I understand d5380001 should be emulated in cpufeature.c but
it is not. What could be wrong here?



-- 
With best regards,
Matwey V. Kornilov

undefined instruction d5380001

[Dave Martin]

On Fri, Sep 29, 2017 at 10:23:54PM +0300, Matwey V. Kornilov wrote:
> Hello,
> 
> I am running 4.13.3 on rockchip 3328 platform(aarch64) with glibc 2.26
> and see the following at booting:
> 
> [   11.152061] modprobe[93]: undefined instruction: pc=0000ffff8ca48ff4
> [   11.152707] Code: d503201f 8a180320 92750001 365ffc20 (d5380001)
> [   11.154347] modprobe[94]: undefined instruction: pc=0000ffff94243ff4
> [   11.154991] Code: d503201f 8a180320 92750001 365ffc20 (d5380001)
> [   11.157070] modprobe[97]: undefined instruction: pc=0000ffff839a0ff4
> [   11.157715] Code: d503201f 8a180320 92750001 365ffc20 (d5380001)
> [   11.159265] modprobe[98]: undefined instruction: pc=0000ffffb0591ff4
> [   11.159908] Code: d503201f 8a180320 92750001 365ffc20 (d5380001)
> 
> As far as I understand d5380001 should be emulated in cpufeature.c but
> it is not. What could be wrong here?

The whole sequence is

   0:   d503201f        nop
   4:   8a180320        and     x0, x25, x24
   8:   92750001        and     x1, x0, #0x800
   c:   365ffc20        tbz     w0, #11, 0xffffffffffffff90
  10:*  d5380001        mrs     x1, midr_el1            <-- trapping instruction

I'm _guessing_ this is the glibc startup code, or otherwise something
similar:

http://www.sourceware.org/git/?p=glibc.git;a=blob;f=sysdeps/unix/sysv/linux/aarch64/cpu-features.c;h=0275d11c7fa5cba02f3173db25a8a02993e92b7e;hb=1c9a5c270d8b66f30dcfaf1cb2d6cf39d3e18369#l46

The emulation is not guaranteed to work if HWCAP_CPUID (1 << 11) is not
set, but this code does seem to be checking correctly, and v4.13 should
unconditionally set this hwcap and emulate MRS.

So no, I don't know what's going wrong here.


What should happen here is that the do_undefinstr() in
arch/arm64/kernel/traps.c should call registered undef hooks until it
finds one that accepts the faulting instruction.

So, either the cpufeatures undef hook is not getting called, or it is
failing the instruction somewhere, possibly in
cpufeatures.c:emulate_id_reg() or emulate_sys_reg().


Can you add some trace to those functions to see what's happening?

Cc'ing Suzuki, who knows this code better than me and may have some
ideas.

Cheers
---Dave

undefined instruction d5380001 (arm64 mrs emulation)

[James Morse]

Hi Matwey,

On 02/10/17 12:24, Dave Martin wrote:
> On Fri, Sep 29, 2017 at 10:23:54PM +0300, Matwey V. Kornilov wrote:
>> I am running 4.13.3 on rockchip 3328 platform(aarch64) with glibc 2.26
>> and see the following at booting:
>>
>> [   11.152061] modprobe[93]: undefined instruction: pc=0000ffff8ca48ff4
>> [   11.152707] Code: d503201f 8a180320 92750001 365ffc20 (d5380001)
>> [   11.154347] modprobe[94]: undefined instruction: pc=0000ffff94243ff4
>> [   11.154991] Code: d503201f 8a180320 92750001 365ffc20 (d5380001)
>> [   11.157070] modprobe[97]: undefined instruction: pc=0000ffff839a0ff4
>> [   11.157715] Code: d503201f 8a180320 92750001 365ffc20 (d5380001)
>> [   11.159265] modprobe[98]: undefined instruction: pc=0000ffffb0591ff4
>> [   11.159908] Code: d503201f 8a180320 92750001 365ffc20 (d5380001)
>>
>> As far as I understand d5380001 should be emulated in cpufeature.c but
>> it is not. What could be wrong here?
> 
> The whole sequence is
> 
>    0:   d503201f        nop
>    4:   8a180320        and     x0, x25, x24
>    8:   92750001        and     x1, x0, #0x800
>    c:   365ffc20        tbz     w0, #11, 0xffffffffffffff90
>   10:*  d5380001        mrs     x1, midr_el1            <-- trapping instruction

This looks the same as:
https://bugzilla.redhat.com/show_bug.cgi?id=1496209

[...]

> What should happen here is that the do_undefinstr() in
> arch/arm64/kernel/traps.c should call registered undef hooks until it
> finds one that accepts the faulting instruction.
> 
> So, either the cpufeatures undef hook is not getting called, or it is
> failing the instruction somewhere, possibly in
> cpufeatures.c:emulate_id_reg() or emulate_sys_reg().
> 
> 
> Can you add some trace to those functions to see what's happening?

I couldn't reproduce this with linux-stable's v4.13.3 defconfig on Seattle or Juno.

What distribution are you running? Could you also try [0] to see if this is
something specific to your version of modprobe?


Thanks,

James

[0] works for me:
---------------------%<---------------------
#include <stdio.h>
#include <sys/auxv.h>

#ifndef HWCAP_CPUID
#define HWCAP_CPUID (1 << 11)
#endif

int main(int argc, char **argv)
{
        register unsigned int midr asm ("r1") = 0;
        unsigned long hwcaps = getauxval(AT_HWCAP);

        if (!(hwcaps & HWCAP_CPUID)) {
                fprintf(stderr, "mrs emulation not supported\n");
                return 1;
        }

        asm("mrs %0, midr_el1" : "=r"(midr));

        fprintf(stderr, "mrs x1, midr_el1; x1=0x%x\n", midr);

        return 0;
}
---------------------%<---------------------

undefined instruction d5380001 (arm64 mrs emulation)

[Suzuki K Poulose]

On Mon, Oct 02, 2017 at 03:11:18PM +0100, James Morse wrote:
> Hi Matwey,
> 
> On 02/10/17 12:24, Dave Martin wrote:
> > On Fri, Sep 29, 2017 at 10:23:54PM +0300, Matwey V. Kornilov wrote:
> >> I am running 4.13.3 on rockchip 3328 platform(aarch64) with glibc 2.26
> >> and see the following at booting:
> >>
> >> [   11.152061] modprobe[93]: undefined instruction: pc=0000ffff8ca48ff4
> >> [   11.152707] Code: d503201f 8a180320 92750001 365ffc20 (d5380001)
> >> [   11.154347] modprobe[94]: undefined instruction: pc=0000ffff94243ff4
> >> [   11.154991] Code: d503201f 8a180320 92750001 365ffc20 (d5380001)
> >> [   11.157070] modprobe[97]: undefined instruction: pc=0000ffff839a0ff4
> >> [   11.157715] Code: d503201f 8a180320 92750001 365ffc20 (d5380001)
> >> [   11.159265] modprobe[98]: undefined instruction: pc=0000ffffb0591ff4
> >> [   11.159908] Code: d503201f 8a180320 92750001 365ffc20 (d5380001)
> >>
> >> As far as I understand d5380001 should be emulated in cpufeature.c but
> >> it is not. What could be wrong here?
> > 
> > The whole sequence is
> > 
> >    0:   d503201f        nop
> >    4:   8a180320        and     x0, x25, x24
> >    8:   92750001        and     x1, x0, #0x800
> >    c:   365ffc20        tbz     w0, #11, 0xffffffffffffff90
> >   10:*  d5380001        mrs     x1, midr_el1            <-- trapping instruction
> 
> This looks the same as:
> https://bugzilla.redhat.com/show_bug.cgi?id=1496209
> 
> [...]
> 
> > What should happen here is that the do_undefinstr() in
> > arch/arm64/kernel/traps.c should call registered undef hooks until it
> > finds one that accepts the faulting instruction.
> > 
> > So, either the cpufeatures undef hook is not getting called, or it is
> > failing the instruction somewhere, possibly in
> > cpufeatures.c:emulate_id_reg() or emulate_sys_reg().
> > 
> > 
> > Can you add some trace to those functions to see what's happening?
> 
> I couldn't reproduce this with linux-stable's v4.13.3 defconfig on Seattle or Juno.
> 
> What distribution are you running? Could you also try [0] to see if this is
> something specific to your version of modprobe?


It is worth noting that we register the MRS instruction handler as late_init call.
Now the question is how late that could be. Given that we are hitting it with
modprobe, which could be used for requesting modules from initrd. Also which explains
why it we can't reproduce it by simple testcases, after it was registered.

Now the question is, how early do we want to push this. Since it doesn't depend really
on any other subsystem, we could move it as early as "early". Or for keeping it in
line with other "arch" specific init calls, we could simply make it arch_initcall.

Matwey,

Please could you check if the following patch fixes the issue for you:

Cheers
Suzuki

----8>----

arm64: Enable MRS emulation early enough in the boot sequence
   
Make sure the MRS emulation is enabled early enough that the
early userspace applications (e.g, those run from initrd) could
run without any trouble.
 
Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com>

diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
index 9f9e0064c8c1..048f5469531f 100644
--- a/arch/arm64/kernel/cpufeature.c
+++ b/arch/arm64/kernel/cpufeature.c
@@ -1294,4 +1294,4 @@ static int __init enable_mrs_emulation(void)
 	return 0;
 }
 
-late_initcall(enable_mrs_emulation);
+arch_initcall(enable_mrs_emulation);
---


> 
> 
> Thanks,
>
> James
> 
> [0] works for me:
> ---------------------%<---------------------
> #include <stdio.h>
> #include <sys/auxv.h>
> 
> #ifndef HWCAP_CPUID
> #define HWCAP_CPUID (1 << 11)
> #endif
> 
> int main(int argc, char **argv)
> {
>         register unsigned int midr asm ("r1") = 0;
>         unsigned long hwcaps = getauxval(AT_HWCAP);
> 
>         if (!(hwcaps & HWCAP_CPUID)) {
>                 fprintf(stderr, "mrs emulation not supported\n");
>                 return 1;
>         }
> 
>         asm("mrs %0, midr_el1" : "=r"(midr));
> 
>         fprintf(stderr, "mrs x1, midr_el1; x1=0x%x\n", midr);
> 
>         return 0;
> }
> ---------------------%<---------------------
> 

undefined instruction d5380001 (arm64 mrs emulation)

[Matwey V. Kornilov]

The patch helps to overcome the issue, Probably it should be applied
to all stable releases affected by this behaviour.
modprobe in initrd may load quite required things.


2017-10-02 18:56 GMT+03:00 Suzuki K Poulose <Suzuki.Poulose@arm.com>:
> On Mon, Oct 02, 2017 at 03:11:18PM +0100, James Morse wrote:
>> Hi Matwey,
>>
>> On 02/10/17 12:24, Dave Martin wrote:
>> > On Fri, Sep 29, 2017 at 10:23:54PM +0300, Matwey V. Kornilov wrote:
>> >> I am running 4.13.3 on rockchip 3328 platform(aarch64) with glibc 2.26
>> >> and see the following at booting:
>> >>
>> >> [   11.152061] modprobe[93]: undefined instruction: pc=0000ffff8ca48ff4
>> >> [   11.152707] Code: d503201f 8a180320 92750001 365ffc20 (d5380001)
>> >> [   11.154347] modprobe[94]: undefined instruction: pc=0000ffff94243ff4
>> >> [   11.154991] Code: d503201f 8a180320 92750001 365ffc20 (d5380001)
>> >> [   11.157070] modprobe[97]: undefined instruction: pc=0000ffff839a0ff4
>> >> [   11.157715] Code: d503201f 8a180320 92750001 365ffc20 (d5380001)
>> >> [   11.159265] modprobe[98]: undefined instruction: pc=0000ffffb0591ff4
>> >> [   11.159908] Code: d503201f 8a180320 92750001 365ffc20 (d5380001)
>> >>
>> >> As far as I understand d5380001 should be emulated in cpufeature.c but
>> >> it is not. What could be wrong here?
>> >
>> > The whole sequence is
>> >
>> >    0:   d503201f        nop
>> >    4:   8a180320        and     x0, x25, x24
>> >    8:   92750001        and     x1, x0, #0x800
>> >    c:   365ffc20        tbz     w0, #11, 0xffffffffffffff90
>> >   10:*  d5380001        mrs     x1, midr_el1            <-- trapping instruction
>>
>> This looks the same as:
>> https://bugzilla.redhat.com/show_bug.cgi?id=1496209
>>
>> [...]
>>
>> > What should happen here is that the do_undefinstr() in
>> > arch/arm64/kernel/traps.c should call registered undef hooks until it
>> > finds one that accepts the faulting instruction.
>> >
>> > So, either the cpufeatures undef hook is not getting called, or it is
>> > failing the instruction somewhere, possibly in
>> > cpufeatures.c:emulate_id_reg() or emulate_sys_reg().
>> >
>> >
>> > Can you add some trace to those functions to see what's happening?
>>
>> I couldn't reproduce this with linux-stable's v4.13.3 defconfig on Seattle or Juno.
>>
>> What distribution are you running? Could you also try [0] to see if this is
>> something specific to your version of modprobe?
>
>
> It is worth noting that we register the MRS instruction handler as late_init call.
> Now the question is how late that could be. Given that we are hitting it with
> modprobe, which could be used for requesting modules from initrd. Also which explains
> why it we can't reproduce it by simple testcases, after it was registered.
>
> Now the question is, how early do we want to push this. Since it doesn't depend really
> on any other subsystem, we could move it as early as "early". Or for keeping it in
> line with other "arch" specific init calls, we could simply make it arch_initcall.
>
> Matwey,
>
> Please could you check if the following patch fixes the issue for you:
>
> Cheers
> Suzuki
>
> ----8>----
>
> arm64: Enable MRS emulation early enough in the boot sequence
>
> Make sure the MRS emulation is enabled early enough that the
> early userspace applications (e.g, those run from initrd) could
> run without any trouble.
>
> Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com>
>
> diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
> index 9f9e0064c8c1..048f5469531f 100644
> --- a/arch/arm64/kernel/cpufeature.c
> +++ b/arch/arm64/kernel/cpufeature.c
> @@ -1294,4 +1294,4 @@ static int __init enable_mrs_emulation(void)
>         return 0;
>  }
>
> -late_initcall(enable_mrs_emulation);
> +arch_initcall(enable_mrs_emulation);
> ---
>
>
>>
>>
>> Thanks,
>>
>> James
>>
>> [0] works for me:
>> ---------------------%<---------------------
>> #include <stdio.h>
>> #include <sys/auxv.h>
>>
>> #ifndef HWCAP_CPUID
>> #define HWCAP_CPUID (1 << 11)
>> #endif
>>
>> int main(int argc, char **argv)
>> {
>>         register unsigned int midr asm ("r1") = 0;
>>         unsigned long hwcaps = getauxval(AT_HWCAP);
>>
>>         if (!(hwcaps & HWCAP_CPUID)) {
>>                 fprintf(stderr, "mrs emulation not supported\n");
>>                 return 1;
>>         }
>>
>>         asm("mrs %0, midr_el1" : "=r"(midr));
>>
>>         fprintf(stderr, "mrs x1, midr_el1; x1=0x%x\n", midr);
>>
>>         return 0;
>> }
>> ---------------------%<---------------------
>>



-- 
With best regards,
Matwey V. Kornilov

undefined instruction d5380001 (arm64 mrs emulation)

[Matthias Brugger]

Hi all,
Hi Greg,
On 10/04/2017 11:11 AM, Matwey V. Kornilov wrote:
> The patch helps to overcome the issue, Probably it should be applied
> to all stable releases affected by this behaviour.
> modprobe in initrd may load quite required things.
> 
> 
> 2017-10-02 18:56 GMT+03:00 Suzuki K Poulose <Suzuki.Poulose@arm.com>:
>> On Mon, Oct 02, 2017 at 03:11:18PM +0100, James Morse wrote:
>>> Hi Matwey,
>>>
>>> On 02/10/17 12:24, Dave Martin wrote:
>>>> On Fri, Sep 29, 2017 at 10:23:54PM +0300, Matwey V. Kornilov wrote:
>>>>> I am running 4.13.3 on rockchip 3328 platform(aarch64) with glibc 2.26
>>>>> and see the following at booting:
>>>>>
>>>>> [   11.152061] modprobe[93]: undefined instruction: pc=0000ffff8ca48ff4
>>>>> [   11.152707] Code: d503201f 8a180320 92750001 365ffc20 (d5380001)
>>>>> [   11.154347] modprobe[94]: undefined instruction: pc=0000ffff94243ff4
>>>>> [   11.154991] Code: d503201f 8a180320 92750001 365ffc20 (d5380001)
>>>>> [   11.157070] modprobe[97]: undefined instruction: pc=0000ffff839a0ff4
>>>>> [   11.157715] Code: d503201f 8a180320 92750001 365ffc20 (d5380001)
>>>>> [   11.159265] modprobe[98]: undefined instruction: pc=0000ffffb0591ff4
>>>>> [   11.159908] Code: d503201f 8a180320 92750001 365ffc20 (d5380001)
>>>>>
>>>>> As far as I understand d5380001 should be emulated in cpufeature.c but
>>>>> it is not. What could be wrong here?
>>>>
>>>> The whole sequence is
>>>>
>>>>     0:   d503201f        nop
>>>>     4:   8a180320        and     x0, x25, x24
>>>>     8:   92750001        and     x1, x0, #0x800
>>>>     c:   365ffc20        tbz     w0, #11, 0xffffffffffffff90
>>>>    10:*  d5380001        mrs     x1, midr_el1            <-- trapping instruction
>>>
>>> This looks the same as:
>>> https://bugzilla.redhat.com/show_bug.cgi?id=1496209
>>>
>>> [...]
>>>
>>>> What should happen here is that the do_undefinstr() in
>>>> arch/arm64/kernel/traps.c should call registered undef hooks until it
>>>> finds one that accepts the faulting instruction.
>>>>
>>>> So, either the cpufeatures undef hook is not getting called, or it is
>>>> failing the instruction somewhere, possibly in
>>>> cpufeatures.c:emulate_id_reg() or emulate_sys_reg().
>>>>
>>>>
>>>> Can you add some trace to those functions to see what's happening?
>>>
>>> I couldn't reproduce this with linux-stable's v4.13.3 defconfig on Seattle or Juno.
>>>
>>> What distribution are you running? Could you also try [0] to see if this is
>>> something specific to your version of modprobe?
>>
>>
>> It is worth noting that we register the MRS instruction handler as late_init call.
>> Now the question is how late that could be. Given that we are hitting it with
>> modprobe, which could be used for requesting modules from initrd. Also which explains
>> why it we can't reproduce it by simple testcases, after it was registered.
>>
>> Now the question is, how early do we want to push this. Since it doesn't depend really
>> on any other subsystem, we could move it as early as "early". Or for keeping it in
>> line with other "arch" specific init calls, we could simply make it arch_initcall.
>>
>> Matwey,
>>
>> Please could you check if the following patch fixes the issue for you:
>>
>> Cheers
>> Suzuki
>>
>> ----8>----
>>
>> arm64: Enable MRS emulation early enough in the boot sequence
>>
>> Make sure the MRS emulation is enabled early enough that the
>> early userspace applications (e.g, those run from initrd) could
>> run without any trouble.
>>
>> Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com>
>>
>> diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
>> index 9f9e0064c8c1..048f5469531f 100644
>> --- a/arch/arm64/kernel/cpufeature.c
>> +++ b/arch/arm64/kernel/cpufeature.c
>> @@ -1294,4 +1294,4 @@ static int __init enable_mrs_emulation(void)
>>          return 0;
>>   }
>>
>> -late_initcall(enable_mrs_emulation);
>> +arch_initcall(enable_mrs_emulation);
>> ---
>>
>>

I realized this patch did not land in v4.13.5
Did it got forgotten or are there any concerns?

We also hit this bug in openSUSE Tumbleweed:
https://bugzilla.suse.com/show_bug.cgi?id=1061188

Regards,
Matthias

>>>
>>>
>>> Thanks,
>>>
>>> James
>>>
>>> [0] works for me:
>>> ---------------------%<---------------------
>>> #include <stdio.h>
>>> #include <sys/auxv.h>
>>>
>>> #ifndef HWCAP_CPUID
>>> #define HWCAP_CPUID (1 << 11)
>>> #endif
>>>
>>> int main(int argc, char **argv)
>>> {
>>>          register unsigned int midr asm ("r1") = 0;
>>>          unsigned long hwcaps = getauxval(AT_HWCAP);
>>>
>>>          if (!(hwcaps & HWCAP_CPUID)) {
>>>                  fprintf(stderr, "mrs emulation not supported\n");
>>>                  return 1;
>>>          }
>>>
>>>          asm("mrs %0, midr_el1" : "=r"(midr));
>>>
>>>          fprintf(stderr, "mrs x1, midr_el1; x1=0x%x\n", midr);
>>>
>>>          return 0;
>>> }
>>> ---------------------%<---------------------
>>>
> 
> 
> 

undefined instruction d5380001 (arm64 mrs emulation)

[Mark Rutland]

Hi Matthias,

On Thu, Oct 05, 2017 at 04:54:09PM +0200, Matthias Brugger wrote:
> On 10/04/2017 11:11 AM, Matwey V. Kornilov wrote:
> >The patch helps to overcome the issue, Probably it should be applied
> >to all stable releases affected by this behaviour.
> >modprobe in initrd may load quite required things.
> >
> >2017-10-02 18:56 GMT+03:00 Suzuki K Poulose <Suzuki.Poulose@arm.com>:
> >>arm64: Enable MRS emulation early enough in the boot sequence
> >>
> >>Make sure the MRS emulation is enabled early enough that the
> >>early userspace applications (e.g, those run from initrd) could
> >>run without any trouble.
> >>
> >>Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com>
> >>
> >>diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
> >>index 9f9e0064c8c1..048f5469531f 100644
> >>--- a/arch/arm64/kernel/cpufeature.c
> >>+++ b/arch/arm64/kernel/cpufeature.c
> >>@@ -1294,4 +1294,4 @@ static int __init enable_mrs_emulation(void)
> >>         return 0;
> >>  }
> >>
> >>-late_initcall(enable_mrs_emulation);
> >>+arch_initcall(enable_mrs_emulation);
> >>---
> >>
> >>
> 
> I realized this patch did not land in v4.13.5
> Did it got forgotten or are there any concerns?

This patch wasn't a complete fix, and the issue is still being discussed
at:

http://lists.infradead.org/pipermail/linux-arm-kernel/2017-October/534396.html

Thanks,
Mark.

undefined instruction d5380001 (arm64 mrs emulation)

[Catalin Marinas]

Hi Matthias,

On Thu, Oct 05, 2017 at 04:54:09PM +0200, Matthias Brugger wrote:
> On 10/04/2017 11:11 AM, Matwey V. Kornilov wrote:
> > The patch helps to overcome the issue, Probably it should be applied
> > to all stable releases affected by this behaviour.
> > modprobe in initrd may load quite required things.
> > 
> > 2017-10-02 18:56 GMT+03:00 Suzuki K Poulose <Suzuki.Poulose@arm.com>:
> > > On Mon, Oct 02, 2017 at 03:11:18PM +0100, James Morse wrote:
> > > > On 02/10/17 12:24, Dave Martin wrote:
> > > > > On Fri, Sep 29, 2017 at 10:23:54PM +0300, Matwey V. Kornilov wrote:
> > > > > > I am running 4.13.3 on rockchip 3328 platform(aarch64) with glibc 2.26
> > > > > > and see the following at booting:
> > > > > > 
> > > > > > [   11.152061] modprobe[93]: undefined instruction: pc=0000ffff8ca48ff4
> > > > > > [   11.152707] Code: d503201f 8a180320 92750001 365ffc20 (d5380001)
> > > > > > [   11.154347] modprobe[94]: undefined instruction: pc=0000ffff94243ff4
> > > > > > [   11.154991] Code: d503201f 8a180320 92750001 365ffc20 (d5380001)
> > > > > > [   11.157070] modprobe[97]: undefined instruction: pc=0000ffff839a0ff4
> > > > > > [   11.157715] Code: d503201f 8a180320 92750001 365ffc20 (d5380001)
> > > > > > [   11.159265] modprobe[98]: undefined instruction: pc=0000ffffb0591ff4
> > > > > > [   11.159908] Code: d503201f 8a180320 92750001 365ffc20 (d5380001)
> > > > > > 
> > > > > > As far as I understand d5380001 should be emulated in cpufeature.c but
> > > > > > it is not. What could be wrong here?
> > > > > 
> > > > > The whole sequence is
> > > > > 
> > > > >     0:   d503201f        nop
> > > > >     4:   8a180320        and     x0, x25, x24
> > > > >     8:   92750001        and     x1, x0, #0x800
> > > > >     c:   365ffc20        tbz     w0, #11, 0xffffffffffffff90
> > > > >    10:*  d5380001        mrs     x1, midr_el1            <-- trapping instruction
> > > > 
> > > > This looks the same as:
> > > > https://bugzilla.redhat.com/show_bug.cgi?id=1496209
> > > > 
> > > > [...]
> > > > 
> > > > > What should happen here is that the do_undefinstr() in
> > > > > arch/arm64/kernel/traps.c should call registered undef hooks until it
> > > > > finds one that accepts the faulting instruction.
> > > > > 
> > > > > So, either the cpufeatures undef hook is not getting called, or it is
> > > > > failing the instruction somewhere, possibly in
> > > > > cpufeatures.c:emulate_id_reg() or emulate_sys_reg().
> > > > > 
> > > > > 
> > > > > Can you add some trace to those functions to see what's happening?
> > > > 
> > > > I couldn't reproduce this with linux-stable's v4.13.3 defconfig on Seattle or Juno.
> > > > 
> > > > What distribution are you running? Could you also try [0] to see if this is
> > > > something specific to your version of modprobe?
> > > 
> > > 
> > > It is worth noting that we register the MRS instruction handler as late_init call.
> > > Now the question is how late that could be. Given that we are hitting it with
> > > modprobe, which could be used for requesting modules from initrd. Also which explains
> > > why it we can't reproduce it by simple testcases, after it was registered.
> > > 
> > > Now the question is, how early do we want to push this. Since it doesn't depend really
> > > on any other subsystem, we could move it as early as "early". Or for keeping it in
> > > line with other "arch" specific init calls, we could simply make it arch_initcall.
> > > 
> > > Matwey,
> > > 
> > > Please could you check if the following patch fixes the issue for you:
> > > 
> > > Cheers
> > > Suzuki
> > > 
> > > ----8>----
> > > 
> > > arm64: Enable MRS emulation early enough in the boot sequence
> > > 
> > > Make sure the MRS emulation is enabled early enough that the
> > > early userspace applications (e.g, those run from initrd) could
> > > run without any trouble.
> > > 
> > > Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com>
> > > 
> > > diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
> > > index 9f9e0064c8c1..048f5469531f 100644
> > > --- a/arch/arm64/kernel/cpufeature.c
> > > +++ b/arch/arm64/kernel/cpufeature.c
> > > @@ -1294,4 +1294,4 @@ static int __init enable_mrs_emulation(void)
> > >          return 0;
> > >   }
> > > 
> > > -late_initcall(enable_mrs_emulation);
> > > +arch_initcall(enable_mrs_emulation);
> > > ---
> 
> I realized this patch did not land in v4.13.5
> Did it got forgotten or are there any concerns?
> 
> We also hit this bug in openSUSE Tumbleweed:
> https://bugzilla.suse.com/show_bug.cgi?id=1061188

As Mark replied, we are still debating why this happens and whether the
above fix is sufficient. As we were digging further, we realised there
is no clear init level after which user space can be invoked, which
means Suzuki's patch may not always be sufficient.

I proposed something as a way of spotting this issue early [1] but I
need to post it on the linux-arch to get some consensus.

Can you post the full kernel log somewhere? I'm trying to figure out
what trigged the modprobe during the kernel boot.

Thanks,

Catalin

[1] http://lists.infradead.org/pipermail/linux-arm-kernel/2017-October/534465.html

undefined instruction d5380001 (arm64 mrs emulation)

[Matthias Brugger]

Hi Catalin,

On 10/05/2017 06:16 PM, Catalin Marinas wrote:
> Hi Matthias,
> 
> On Thu, Oct 05, 2017 at 04:54:09PM +0200, Matthias Brugger wrote:
>> On 10/04/2017 11:11 AM, Matwey V. Kornilov wrote:
>>> The patch helps to overcome the issue, Probably it should be applied
>>> to all stable releases affected by this behaviour.
>>> modprobe in initrd may load quite required things.
>>>
>>> 2017-10-02 18:56 GMT+03:00 Suzuki K Poulose <Suzuki.Poulose@arm.com>:
>>>> On Mon, Oct 02, 2017 at 03:11:18PM +0100, James Morse wrote:
>>>>> On 02/10/17 12:24, Dave Martin wrote:
>>>>>> On Fri, Sep 29, 2017 at 10:23:54PM +0300, Matwey V. Kornilov wrote:
>>>>>>> I am running 4.13.3 on rockchip 3328 platform(aarch64) with glibc 2.26
>>>>>>> and see the following at booting:
>>>>>>>
>>>>>>> [   11.152061] modprobe[93]: undefined instruction: pc=0000ffff8ca48ff4
>>>>>>> [   11.152707] Code: d503201f 8a180320 92750001 365ffc20 (d5380001)
>>>>>>> [   11.154347] modprobe[94]: undefined instruction: pc=0000ffff94243ff4
>>>>>>> [   11.154991] Code: d503201f 8a180320 92750001 365ffc20 (d5380001)
>>>>>>> [   11.157070] modprobe[97]: undefined instruction: pc=0000ffff839a0ff4
>>>>>>> [   11.157715] Code: d503201f 8a180320 92750001 365ffc20 (d5380001)
>>>>>>> [   11.159265] modprobe[98]: undefined instruction: pc=0000ffffb0591ff4
>>>>>>> [   11.159908] Code: d503201f 8a180320 92750001 365ffc20 (d5380001)
>>>>>>>
>>>>>>> As far as I understand d5380001 should be emulated in cpufeature.c but
>>>>>>> it is not. What could be wrong here?
>>>>>>
>>>>>> The whole sequence is
>>>>>>
>>>>>>      0:   d503201f        nop
>>>>>>      4:   8a180320        and     x0, x25, x24
>>>>>>      8:   92750001        and     x1, x0, #0x800
>>>>>>      c:   365ffc20        tbz     w0, #11, 0xffffffffffffff90
>>>>>>     10:*  d5380001        mrs     x1, midr_el1            <-- trapping instruction
>>>>>
>>>>> This looks the same as:
>>>>> https://bugzilla.redhat.com/show_bug.cgi?id=1496209
>>>>>
>>>>> [...]
>>>>>
>>>>>> What should happen here is that the do_undefinstr() in
>>>>>> arch/arm64/kernel/traps.c should call registered undef hooks until it
>>>>>> finds one that accepts the faulting instruction.
>>>>>>
>>>>>> So, either the cpufeatures undef hook is not getting called, or it is
>>>>>> failing the instruction somewhere, possibly in
>>>>>> cpufeatures.c:emulate_id_reg() or emulate_sys_reg().
>>>>>>
>>>>>>
>>>>>> Can you add some trace to those functions to see what's happening?
>>>>>
>>>>> I couldn't reproduce this with linux-stable's v4.13.3 defconfig on Seattle or Juno.
>>>>>
>>>>> What distribution are you running? Could you also try [0] to see if this is
>>>>> something specific to your version of modprobe?
>>>>
>>>>
>>>> It is worth noting that we register the MRS instruction handler as late_init call.
>>>> Now the question is how late that could be. Given that we are hitting it with
>>>> modprobe, which could be used for requesting modules from initrd. Also which explains
>>>> why it we can't reproduce it by simple testcases, after it was registered.
>>>>
>>>> Now the question is, how early do we want to push this. Since it doesn't depend really
>>>> on any other subsystem, we could move it as early as "early". Or for keeping it in
>>>> line with other "arch" specific init calls, we could simply make it arch_initcall.
>>>>
>>>> Matwey,
>>>>
>>>> Please could you check if the following patch fixes the issue for you:
>>>>
>>>> Cheers
>>>> Suzuki
>>>>
>>>> ----8>----
>>>>
>>>> arm64: Enable MRS emulation early enough in the boot sequence
>>>>
>>>> Make sure the MRS emulation is enabled early enough that the
>>>> early userspace applications (e.g, those run from initrd) could
>>>> run without any trouble.
>>>>
>>>> Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com>
>>>>
>>>> diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
>>>> index 9f9e0064c8c1..048f5469531f 100644
>>>> --- a/arch/arm64/kernel/cpufeature.c
>>>> +++ b/arch/arm64/kernel/cpufeature.c
>>>> @@ -1294,4 +1294,4 @@ static int __init enable_mrs_emulation(void)
>>>>           return 0;
>>>>    }
>>>>
>>>> -late_initcall(enable_mrs_emulation);
>>>> +arch_initcall(enable_mrs_emulation);
>>>> ---
>>
>> I realized this patch did not land in v4.13.5
>> Did it got forgotten or are there any concerns?
>>
>> We also hit this bug in openSUSE Tumbleweed:
>> https://bugzilla.suse.com/show_bug.cgi?id=1061188
> 
> As Mark replied, we are still debating why this happens and whether the
> above fix is sufficient. As we were digging further, we realised there
> is no clear init level after which user space can be invoked, which
> means Suzuki's patch may not always be sufficient.
> 
> I proposed something as a way of spotting this issue early [1] but I
> need to post it on the linux-arch to get some consensus.
> 
> Can you post the full kernel log somewhere? I'm trying to figure out
> what trigged the modprobe during the kernel boot.
> 

You can find the kernel log here:
https://bugzilla.suse.com/attachment.cgi?id=743311

Regards,
Matthias

> Thanks,
> 
> Catalin
> 
> [1] http://lists.infradead.org/pipermail/linux-arm-kernel/2017-October/534465.html
> 

undefined instruction d5380001 (arm64 mrs emulation)

[Catalin Marinas]

On Fri, Oct 06, 2017 at 02:05:09PM +0200, Matthias Brugger wrote:
> On 10/05/2017 06:16 PM, Catalin Marinas wrote:
> > On Thu, Oct 05, 2017 at 04:54:09PM +0200, Matthias Brugger wrote:
> > > We also hit this bug in openSUSE Tumbleweed:
> > > https://bugzilla.suse.com/show_bug.cgi?id=1061188
> > 
> > As Mark replied, we are still debating why this happens and whether the
> > above fix is sufficient. As we were digging further, we realised there
> > is no clear init level after which user space can be invoked, which
> > means Suzuki's patch may not always be sufficient.
> > 
> > I proposed something as a way of spotting this issue early [1] but I
> > need to post it on the linux-arch to get some consensus.
> > 
> > Can you post the full kernel log somewhere? I'm trying to figure out
> > what trigged the modprobe during the kernel boot.
> > 
> 
> You can find the kernel log here:
> https://bugzilla.suse.com/attachment.cgi?id=743311

Thanks, it seems that ipv6 module loading triggered this.

Talking to Suzuki, we came to the conclusion that such thing cannot
happen before rootfs_initcall, so his original core_initcall change
should suffice. I'll push a patch out, hopefully for -rc4 and cc stable.

-- 
Catalin

undefined instruction d5380001 (arm64 mrs emulation)

[Matthias Brugger]

On 10/06/2017 03:13 PM, Catalin Marinas wrote:
> On Fri, Oct 06, 2017 at 02:05:09PM +0200, Matthias Brugger wrote:
>> On 10/05/2017 06:16 PM, Catalin Marinas wrote:
>>> On Thu, Oct 05, 2017 at 04:54:09PM +0200, Matthias Brugger wrote:
>>>> We also hit this bug in openSUSE Tumbleweed:
>>>> https://bugzilla.suse.com/show_bug.cgi?id=1061188
>>>
>>> As Mark replied, we are still debating why this happens and whether the
>>> above fix is sufficient. As we were digging further, we realised there
>>> is no clear init level after which user space can be invoked, which
>>> means Suzuki's patch may not always be sufficient.
>>>
>>> I proposed something as a way of spotting this issue early [1] but I
>>> need to post it on the linux-arch to get some consensus.
>>>
>>> Can you post the full kernel log somewhere? I'm trying to figure out
>>> what trigged the modprobe during the kernel boot.
>>>
>>
>> You can find the kernel log here:
>> https://bugzilla.suse.com/attachment.cgi?id=743311
> 
> Thanks, it seems that ipv6 module loading triggered this.
> 
> Talking to Suzuki, we came to the conclusion that such thing cannot
> happen before rootfs_initcall, so his original core_initcall change
> should suffice. I'll push a patch out, hopefully for -rc4 and cc stable.
> 

Thanks for the info.
Matthias