[PATCH v2 1/2] powerpc: add `cur_cpu_spec` symbol to vmcoreinfo

[PATCH v2 1/2] powerpc: add `cur_cpu_spec` symbol to vmcoreinfo

[Aditya Gupta]

Since below commit, address mapping for vmemmap has changed for Radix
MMU, where address mapping is stored in kernel page table itself,
instead of earlier used 'vmemmap_list'.

    commit 368a0590d954 ("powerpc/book3s64/vmemmap: switch radix to use
    a different vmemmap handling function")

Hence with upstream kernel, in case of Radix MMU, makedumpfile fails to do
address translation for vmemmap addresses, as it depended on vmemmap_list,
which can now be empty.

While fixing the address translation in makedumpfile, it was identified
that currently makedumpfile cannot distinguish between Hash MMU and
Radix MMU, unless VMLINUX is passed with -x flag to makedumpfile.
And hence fails to assign offsets and shifts correctly (such as in L4 to
PGDIR offset calculation in makedumpfile).

For getting the MMU, makedumpfile uses `cur_cpu_spec.mmu_features`.

Add `cur_cpu_spec` symbol and offset of `mmu_features` in the
`cpu_spec` struct, to VMCOREINFO, so that makedumpfile can assign the
offsets correctly, without needing a VMLINUX.

Fixes: 368a0590d954 ("powerpc/book3s64/vmemmap: switch radix to use a different vmemmap handling function")
Reported-by: Sachin Sant <sachinp@linux.ibm.com>
Tested-by: Sachin Sant <sachinp@linux.ibm.com>
Signed-off-by: Aditya Gupta <adityag@linux.ibm.com>

---
Corresponding makedumpfile patches to fix address translation, in Radix
MMU case:

Link: https://lore.kernel.org/kexec/B5F0F00E-F2B1-47D7-A143-5683D10DC29A@linux.ibm.com/T/#t
---
---
 arch/powerpc/kexec/core.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/arch/powerpc/kexec/core.c b/arch/powerpc/kexec/core.c
index de64c7962991..369b8334a4f0 100644
--- a/arch/powerpc/kexec/core.c
+++ b/arch/powerpc/kexec/core.c
@@ -63,6 +63,8 @@ void arch_crash_save_vmcoreinfo(void)
 #ifndef CONFIG_NUMA
 	VMCOREINFO_SYMBOL(contig_page_data);
 #endif
+	VMCOREINFO_SYMBOL(cur_cpu_spec);
+	VMCOREINFO_OFFSET(cpu_spec, mmu_features);
 #if defined(CONFIG_PPC64) && defined(CONFIG_SPARSEMEM_VMEMMAP)
 	VMCOREINFO_SYMBOL(vmemmap_list);
 	VMCOREINFO_SYMBOL(mmu_vmemmap_psize);
-- 
2.41.0

[PATCH v2 2/2] powerpc: add cpu_spec.cpu_features to vmcoreinfo

[Aditya Gupta]

CPU features can be determined in makedumpfile, using
'cur_cpu_spec.cpu_features'.

This provides more data to makedumpfile about the crashed system, and
can help in filtering the vmcore accordingly.

Signed-off-by: Aditya Gupta <adityag@linux.ibm.com>
---
 arch/powerpc/kexec/core.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/arch/powerpc/kexec/core.c b/arch/powerpc/kexec/core.c
index 369b8334a4f0..0d70c7ea820c 100644
--- a/arch/powerpc/kexec/core.c
+++ b/arch/powerpc/kexec/core.c
@@ -64,6 +64,7 @@ void arch_crash_save_vmcoreinfo(void)
 	VMCOREINFO_SYMBOL(contig_page_data);
 #endif
 	VMCOREINFO_SYMBOL(cur_cpu_spec);
+	VMCOREINFO_OFFSET(cpu_spec, cpu_features);
 	VMCOREINFO_OFFSET(cpu_spec, mmu_features);
 #if defined(CONFIG_PPC64) && defined(CONFIG_SPARSEMEM_VMEMMAP)
 	VMCOREINFO_SYMBOL(vmemmap_list);
-- 
2.41.0

Re: [PATCH v2 1/2] powerpc: add `cur_cpu_spec` symbol to vmcoreinfo

[Aneesh Kumar K.V]

Aditya Gupta <adityag@linux.ibm.com> writes:

> Since below commit, address mapping for vmemmap has changed for Radix
> MMU, where address mapping is stored in kernel page table itself,
> instead of earlier used 'vmemmap_list'.
>
>     commit 368a0590d954 ("powerpc/book3s64/vmemmap: switch radix to use
>     a different vmemmap handling function")
>
> Hence with upstream kernel, in case of Radix MMU, makedumpfile fails to do
> address translation for vmemmap addresses, as it depended on vmemmap_list,
> which can now be empty.
>
> While fixing the address translation in makedumpfile, it was identified
> that currently makedumpfile cannot distinguish between Hash MMU and
> Radix MMU, unless VMLINUX is passed with -x flag to makedumpfile.
> And hence fails to assign offsets and shifts correctly (such as in L4 to
> PGDIR offset calculation in makedumpfile).
>
> For getting the MMU, makedumpfile uses `cur_cpu_spec.mmu_features`.
>
> Add `cur_cpu_spec` symbol and offset of `mmu_features` in the
> `cpu_spec` struct, to VMCOREINFO, so that makedumpfile can assign the
> offsets correctly, without needing a VMLINUX.
>
> Fixes: 368a0590d954 ("powerpc/book3s64/vmemmap: switch radix to use a different vmemmap handling function")
> Reported-by: Sachin Sant <sachinp@linux.ibm.com>
> Tested-by: Sachin Sant <sachinp@linux.ibm.com>
> Signed-off-by: Aditya Gupta <adityag@linux.ibm.com>
>
> ---
> Corresponding makedumpfile patches to fix address translation, in Radix
> MMU case:
>
> Link: https://lore.kernel.org/kexec/B5F0F00E-F2B1-47D7-A143-5683D10DC29A@linux.ibm.com/T/#t
> ---
> ---
>  arch/powerpc/kexec/core.c | 2 ++
>  1 file changed, 2 insertions(+)
>
> diff --git a/arch/powerpc/kexec/core.c b/arch/powerpc/kexec/core.c
> index de64c7962991..369b8334a4f0 100644
> --- a/arch/powerpc/kexec/core.c
> +++ b/arch/powerpc/kexec/core.c
> @@ -63,6 +63,8 @@ void arch_crash_save_vmcoreinfo(void)
>  #ifndef CONFIG_NUMA
>  	VMCOREINFO_SYMBOL(contig_page_data);
>  #endif
> +	VMCOREINFO_SYMBOL(cur_cpu_spec);
> +	VMCOREINFO_OFFSET(cpu_spec, mmu_features);
>  #if defined(CONFIG_PPC64) && defined(CONFIG_SPARSEMEM_VMEMMAP)
>  	VMCOREINFO_SYMBOL(vmemmap_list);
>  	VMCOREINFO_SYMBOL(mmu_vmemmap_psize);
>

That implies we now have to be careful when updating MMU_FTR_* #defines.
It is not bad considering other hacks we do in crash to identify kernel
changes tied to version number. But i am wondering if there another way
to identify radix vs hash?

-aneesh

Re: [PATCH v2 1/2] powerpc: add `cur_cpu_spec` symbol to vmcoreinfo

[Aditya Gupta]

On Wed, Sep 20, 2023 at 05:45:36PM +0530, Aneesh Kumar K.V wrote:
> Aditya Gupta <adityag@linux.ibm.com> writes:
> 
> > Since below commit, address mapping for vmemmap has changed for Radix
> > MMU, where address mapping is stored in kernel page table itself,
> > instead of earlier used 'vmemmap_list'.
> >
> >     commit 368a0590d954 ("powerpc/book3s64/vmemmap: switch radix to use
> >     a different vmemmap handling function")
> >
> > Hence with upstream kernel, in case of Radix MMU, makedumpfile fails to do
> > address translation for vmemmap addresses, as it depended on vmemmap_list,
> > which can now be empty.
> >
> > While fixing the address translation in makedumpfile, it was identified
> > that currently makedumpfile cannot distinguish between Hash MMU and
> > Radix MMU, unless VMLINUX is passed with -x flag to makedumpfile.
> > And hence fails to assign offsets and shifts correctly (such as in L4 to
> > PGDIR offset calculation in makedumpfile).
> >
> > For getting the MMU, makedumpfile uses `cur_cpu_spec.mmu_features`.
> >
> > Add `cur_cpu_spec` symbol and offset of `mmu_features` in the
> > `cpu_spec` struct, to VMCOREINFO, so that makedumpfile can assign the
> > offsets correctly, without needing a VMLINUX.
> >
> > Fixes: 368a0590d954 ("powerpc/book3s64/vmemmap: switch radix to use a different vmemmap handling function")
> > Reported-by: Sachin Sant <sachinp@linux.ibm.com>
> > Tested-by: Sachin Sant <sachinp@linux.ibm.com>
> > Signed-off-by: Aditya Gupta <adityag@linux.ibm.com>
> >
> > ---
> > Corresponding makedumpfile patches to fix address translation, in Radix
> > MMU case:
> >
> > Link: https://lore.kernel.org/kexec/B5F0F00E-F2B1-47D7-A143-5683D10DC29A@linux.ibm.com/T/#t
> > ---
> > ---
> >  arch/powerpc/kexec/core.c | 2 ++
> >  1 file changed, 2 insertions(+)
> >
> > diff --git a/arch/powerpc/kexec/core.c b/arch/powerpc/kexec/core.c
> > index de64c7962991..369b8334a4f0 100644
> > --- a/arch/powerpc/kexec/core.c
> > +++ b/arch/powerpc/kexec/core.c
> > @@ -63,6 +63,8 @@ void arch_crash_save_vmcoreinfo(void)
> >  #ifndef CONFIG_NUMA
> >  	VMCOREINFO_SYMBOL(contig_page_data);
> >  #endif
> > +	VMCOREINFO_SYMBOL(cur_cpu_spec);
> > +	VMCOREINFO_OFFSET(cpu_spec, mmu_features);
> >  #if defined(CONFIG_PPC64) && defined(CONFIG_SPARSEMEM_VMEMMAP)
> >  	VMCOREINFO_SYMBOL(vmemmap_list);
> >  	VMCOREINFO_SYMBOL(mmu_vmemmap_psize);
> >
> 
> That implies we now have to be careful when updating MMU_FTR_* #defines.
> It is not bad considering other hacks we do in crash to identify kernel
> changes tied to version number. But i am wondering if there another way
> to identify radix vs hash?
> 

I could not find another way to get any other flag for RADIX vs HASH in
makedumpfile. And currently I don't know of any other way.

Both makedumpfile and crash look for '0x40' flag set in
'cur_cpu_spec.mmu_features', so only requirement for 'MMU_FTR_TYPE_RADIX' is to
be '0x40', or we will need to change the value accordingly in the tools.

Thanks,
- Aditya Gupta

Re: [PATCH v2 1/2] powerpc: add `cur_cpu_spec` symbol to vmcoreinfo

[Aneesh Kumar K.V]

Aditya Gupta <adityag@linux.ibm.com> writes:

> On Wed, Sep 20, 2023 at 05:45:36PM +0530, Aneesh Kumar K.V wrote:
>> Aditya Gupta <adityag@linux.ibm.com> writes:
>> 
>> > Since below commit, address mapping for vmemmap has changed for Radix
>> > MMU, where address mapping is stored in kernel page table itself,
>> > instead of earlier used 'vmemmap_list'.
>> >
>> >     commit 368a0590d954 ("powerpc/book3s64/vmemmap: switch radix to use
>> >     a different vmemmap handling function")
>> >
>> > Hence with upstream kernel, in case of Radix MMU, makedumpfile fails to do
>> > address translation for vmemmap addresses, as it depended on vmemmap_list,
>> > which can now be empty.
>> >
>> > While fixing the address translation in makedumpfile, it was identified
>> > that currently makedumpfile cannot distinguish between Hash MMU and
>> > Radix MMU, unless VMLINUX is passed with -x flag to makedumpfile.
>> > And hence fails to assign offsets and shifts correctly (such as in L4 to
>> > PGDIR offset calculation in makedumpfile).
>> >
>> > For getting the MMU, makedumpfile uses `cur_cpu_spec.mmu_features`.
>> >
>> > Add `cur_cpu_spec` symbol and offset of `mmu_features` in the
>> > `cpu_spec` struct, to VMCOREINFO, so that makedumpfile can assign the
>> > offsets correctly, without needing a VMLINUX.
>> >
>> > Fixes: 368a0590d954 ("powerpc/book3s64/vmemmap: switch radix to use a different vmemmap handling function")
>> > Reported-by: Sachin Sant <sachinp@linux.ibm.com>
>> > Tested-by: Sachin Sant <sachinp@linux.ibm.com>
>> > Signed-off-by: Aditya Gupta <adityag@linux.ibm.com>
>> >
>> > ---
>> > Corresponding makedumpfile patches to fix address translation, in Radix
>> > MMU case:
>> >
>> > Link: https://lore.kernel.org/kexec/B5F0F00E-F2B1-47D7-A143-5683D10DC29A@linux.ibm.com/T/#t
>> > ---
>> > ---
>> >  arch/powerpc/kexec/core.c | 2 ++
>> >  1 file changed, 2 insertions(+)
>> >
>> > diff --git a/arch/powerpc/kexec/core.c b/arch/powerpc/kexec/core.c
>> > index de64c7962991..369b8334a4f0 100644
>> > --- a/arch/powerpc/kexec/core.c
>> > +++ b/arch/powerpc/kexec/core.c
>> > @@ -63,6 +63,8 @@ void arch_crash_save_vmcoreinfo(void)
>> >  #ifndef CONFIG_NUMA
>> >  	VMCOREINFO_SYMBOL(contig_page_data);
>> >  #endif
>> > +	VMCOREINFO_SYMBOL(cur_cpu_spec);
>> > +	VMCOREINFO_OFFSET(cpu_spec, mmu_features);
>> >  #if defined(CONFIG_PPC64) && defined(CONFIG_SPARSEMEM_VMEMMAP)
>> >  	VMCOREINFO_SYMBOL(vmemmap_list);
>> >  	VMCOREINFO_SYMBOL(mmu_vmemmap_psize);
>> >
>> 
>> That implies we now have to be careful when updating MMU_FTR_* #defines.
>> It is not bad considering other hacks we do in crash to identify kernel
>> changes tied to version number. But i am wondering if there another way
>> to identify radix vs hash?
>> 
>
> I could not find another way to get any other flag for RADIX vs HASH in
> makedumpfile. And currently I don't know of any other way.
>
> Both makedumpfile and crash look for '0x40' flag set in
> 'cur_cpu_spec.mmu_features', so only requirement for 'MMU_FTR_TYPE_RADIX' is to
> be '0x40', or we will need to change the value accordingly in the tools.
>

Instead of exporting cur_cpu_spec.mmu_feature, you could do
coreinfo_mmu_features that does

if (radix_enabled())
   coreinfo_mmu_feature = VMCORE_INFO_RADIX_TRANSLATION;

-aneesh

Re: [PATCH v2 1/2] powerpc: add `cur_cpu_spec` symbol to vmcoreinfo

[Michael Ellerman]

"Aneesh Kumar K.V" <aneesh.kumar@linux.ibm.com> writes:
> Aditya Gupta <adityag@linux.ibm.com> writes:
>
>> Since below commit, address mapping for vmemmap has changed for Radix
>> MMU, where address mapping is stored in kernel page table itself,
>> instead of earlier used 'vmemmap_list'.
>>
>>     commit 368a0590d954 ("powerpc/book3s64/vmemmap: switch radix to use
>>     a different vmemmap handling function")
>>
>> Hence with upstream kernel, in case of Radix MMU, makedumpfile fails to do
>> address translation for vmemmap addresses, as it depended on vmemmap_list,
>> which can now be empty.
>>
>> While fixing the address translation in makedumpfile, it was identified
>> that currently makedumpfile cannot distinguish between Hash MMU and
>> Radix MMU, unless VMLINUX is passed with -x flag to makedumpfile.
>> And hence fails to assign offsets and shifts correctly (such as in L4 to
>> PGDIR offset calculation in makedumpfile).
>>
>> For getting the MMU, makedumpfile uses `cur_cpu_spec.mmu_features`.
>>
>> Add `cur_cpu_spec` symbol and offset of `mmu_features` in the
>> `cpu_spec` struct, to VMCOREINFO, so that makedumpfile can assign the
>> offsets correctly, without needing a VMLINUX.
>>
>> Fixes: 368a0590d954 ("powerpc/book3s64/vmemmap: switch radix to use a different vmemmap handling function")
>> Reported-by: Sachin Sant <sachinp@linux.ibm.com>
>> Tested-by: Sachin Sant <sachinp@linux.ibm.com>
>> Signed-off-by: Aditya Gupta <adityag@linux.ibm.com>
>>
>> ---
>> Corresponding makedumpfile patches to fix address translation, in Radix
>> MMU case:
>>
>> Link: https://lore.kernel.org/kexec/B5F0F00E-F2B1-47D7-A143-5683D10DC29A@linux.ibm.com/T/#t
>> ---
>> ---
>>  arch/powerpc/kexec/core.c | 2 ++
>>  1 file changed, 2 insertions(+)
>>
>> diff --git a/arch/powerpc/kexec/core.c b/arch/powerpc/kexec/core.c
>> index de64c7962991..369b8334a4f0 100644
>> --- a/arch/powerpc/kexec/core.c
>> +++ b/arch/powerpc/kexec/core.c
>> @@ -63,6 +63,8 @@ void arch_crash_save_vmcoreinfo(void)
>>  #ifndef CONFIG_NUMA
>>  	VMCOREINFO_SYMBOL(contig_page_data);
>>  #endif
>> +	VMCOREINFO_SYMBOL(cur_cpu_spec);
>> +	VMCOREINFO_OFFSET(cpu_spec, mmu_features);
>>  #if defined(CONFIG_PPC64) && defined(CONFIG_SPARSEMEM_VMEMMAP)
>>  	VMCOREINFO_SYMBOL(vmemmap_list);
>>  	VMCOREINFO_SYMBOL(mmu_vmemmap_psize);
>>
>
> That implies we now have to be careful when updating MMU_FTR_* #defines.
 
Yeah, that's a good point.

> It is not bad considering other hacks we do in crash to identify kernel
> changes tied to version number. But i am wondering if there another way
> to identify radix vs hash?

Ultimately crash just has to accept that the kernel will change over
time, and some times crash will have to adapt.

We can try not to change values unnecessarily, but given the knowledge
of kernel internals crash has there will be breakage from time to time.

The only other alternative I think is to create a well defined data
structure that is explicitly provided by the kernel for crash with
various information in a set format. With a committment that the data
structure will be maintained in a forward-compatible manner. Which
sounds like a bunch of work :)

cheers

Re: [PATCH v2 1/2] powerpc: add `cur_cpu_spec` symbol to vmcoreinfo

[Michael Ellerman]

"Aneesh Kumar K.V" <aneesh.kumar@linux.ibm.com> writes:
> Aditya Gupta <adityag@linux.ibm.com> writes:
>> On Wed, Sep 20, 2023 at 05:45:36PM +0530, Aneesh Kumar K.V wrote:
>>> Aditya Gupta <adityag@linux.ibm.com> writes:
>>>
>>> > Since below commit, address mapping for vmemmap has changed for Radix
>>> > MMU, where address mapping is stored in kernel page table itself,
>>> > instead of earlier used 'vmemmap_list'.
>>> >
>>> >     commit 368a0590d954 ("powerpc/book3s64/vmemmap: switch radix to use
>>> >     a different vmemmap handling function")
>>> >
>>> > Hence with upstream kernel, in case of Radix MMU, makedumpfile fails to do
>>> > address translation for vmemmap addresses, as it depended on vmemmap_list,
>>> > which can now be empty.
>>> >
>>> > While fixing the address translation in makedumpfile, it was identified
>>> > that currently makedumpfile cannot distinguish between Hash MMU and
>>> > Radix MMU, unless VMLINUX is passed with -x flag to makedumpfile.
>>> > And hence fails to assign offsets and shifts correctly (such as in L4 to
>>> > PGDIR offset calculation in makedumpfile).
>>> >
>>> > For getting the MMU, makedumpfile uses `cur_cpu_spec.mmu_features`.
>>> >
>>> > Add `cur_cpu_spec` symbol and offset of `mmu_features` in the
>>> > `cpu_spec` struct, to VMCOREINFO, so that makedumpfile can assign the
>>> > offsets correctly, without needing a VMLINUX.
>>> >
>>> > Fixes: 368a0590d954 ("powerpc/book3s64/vmemmap: switch radix to use a different vmemmap handling function")
>>> > Reported-by: Sachin Sant <sachinp@linux.ibm.com>
>>> > Tested-by: Sachin Sant <sachinp@linux.ibm.com>
>>> > Signed-off-by: Aditya Gupta <adityag@linux.ibm.com>
>>> >
>>> > ---
>>> > Corresponding makedumpfile patches to fix address translation, in Radix
>>> > MMU case:
>>> >
>>> > Link: https://lore.kernel.org/kexec/B5F0F00E-F2B1-47D7-A143-5683D10DC29A@linux.ibm.com/T/#t
>>> > ---
>>> > ---
>>> >  arch/powerpc/kexec/core.c | 2 ++
>>> >  1 file changed, 2 insertions(+)
>>> >
>>> > diff --git a/arch/powerpc/kexec/core.c b/arch/powerpc/kexec/core.c
>>> > index de64c7962991..369b8334a4f0 100644
>>> > --- a/arch/powerpc/kexec/core.c
>>> > +++ b/arch/powerpc/kexec/core.c
>>> > @@ -63,6 +63,8 @@ void arch_crash_save_vmcoreinfo(void)
>>> >  #ifndef CONFIG_NUMA
>>> >  	VMCOREINFO_SYMBOL(contig_page_data);
>>> >  #endif
>>> > +	VMCOREINFO_SYMBOL(cur_cpu_spec);
>>> > +	VMCOREINFO_OFFSET(cpu_spec, mmu_features);
>>> >  #if defined(CONFIG_PPC64) && defined(CONFIG_SPARSEMEM_VMEMMAP)
>>> >  	VMCOREINFO_SYMBOL(vmemmap_list);
>>> >  	VMCOREINFO_SYMBOL(mmu_vmemmap_psize);
>>> >
>>>
>>> That implies we now have to be careful when updating MMU_FTR_* #defines.
>>> It is not bad considering other hacks we do in crash to identify kernel
>>> changes tied to version number. But i am wondering if there another way
>>> to identify radix vs hash?
>>>
>>
>> I could not find another way to get any other flag for RADIX vs HASH in
>> makedumpfile. And currently I don't know of any other way.
>>
>> Both makedumpfile and crash look for '0x40' flag set in
>> 'cur_cpu_spec.mmu_features', so only requirement for 'MMU_FTR_TYPE_RADIX' is to
>> be '0x40', or we will need to change the value accordingly in the tools.
>
> Instead of exporting cur_cpu_spec.mmu_feature, you could do
> coreinfo_mmu_features that does
>
> if (radix_enabled())
>    coreinfo_mmu_feature = VMCORE_INFO_RADIX_TRANSLATION;

On other arches they seem to use vmcoreinfo_append_str() for more things
than we do on powerpc.

eg. x86:

       vmcoreinfo_append_str("NUMBER(pgtable_l5_enabled)=%d\n", pgtable_l5_enabled());

Could we do something like that instead:

       vmcoreinfo_append_str("RADIX_MMU=%d\n", early_radix_enabled());

cheers

Re: [PATCH v2 1/2] powerpc: add `cur_cpu_spec` symbol to vmcoreinfo

[Michael Ellerman]

On Wed, 20 Sep 2023 16:27:05 +0530, Aditya Gupta wrote:
> Since below commit, address mapping for vmemmap has changed for Radix
> MMU, where address mapping is stored in kernel page table itself,
> instead of earlier used 'vmemmap_list'.
> 
>     commit 368a0590d954 ("powerpc/book3s64/vmemmap: switch radix to use
>     a different vmemmap handling function")
> 
> [...]

Patch 2 applied to powerpc/next.

[2/2] powerpc: add cpu_spec.cpu_features to vmcoreinfo
      https://git.kernel.org/powerpc/c/a143892cb77c5397fd4356bbef9982abe4f3c5a5

cheers