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Re: [v3,1/8] powerpc: Create a helper for getting the kernel toc value

Started byMichael Ellerman <mpe@ellerman.id.au>
First post2016-03-14 10:30 +0100
Last post2016-03-17 17:00 +0100
Articles 7 — 4 participants

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  Re: [v3,1/8] powerpc: Create a helper for getting the kernel toc value Michael Ellerman <mpe@ellerman.id.au> - 2016-03-14 10:30 +0100
    Re: [v3,1/8] powerpc: Create a helper for getting the kernel toc  value Jiri Kosina <jikos@kernel.org> - 2016-03-15 02:30 +0100
      Re: [v3,1/8] powerpc: Create a helper for getting the kernel toc  value Michael Ellerman <mpe@ellerman.id.au> - 2016-03-16 11:30 +0100
        Re: [v3,1/8] powerpc: Create a helper for getting the kernel toc  value Torsten Duwe <duwe@lst.de> - 2016-03-16 16:00 +0100
          Re: [v3,1/8] powerpc: Create a helper for getting the kernel toc  value Balbir Singh <bsingharora@gmail.com> - 2016-03-17 01:00 +0100
      Re: [v3,1/8] powerpc: Create a helper for getting the kernel toc  value Balbir Singh <bsingharora@gmail.com> - 2016-03-17 01:00 +0100
        Re: [v3,1/8] powerpc: Create a helper for getting the kernel toc  value Torsten Duwe <duwe@lst.de> - 2016-03-17 17:00 +0100

#1357089 — Re: [v3,1/8] powerpc: Create a helper for getting the kernel toc value

FromMichael Ellerman <mpe@ellerman.id.au>
Date2016-03-14 10:30 +0100
SubjectRe: [v3,1/8] powerpc: Create a helper for getting the kernel toc value
Message-ID<rcwZ3-1Qb-3@gated-at.bofh.it>
On Thu, 2016-03-03 at 04:26:53 UTC, Michael Ellerman wrote:
> Move the logic to work out the kernel toc pointer into a header. This is
> a good cleanup, and also means we can use it elsewhere in future.
> 
> Reviewed-by: Kamalesh Babulal <kamalesh@linux.vnet.ibm.com>
> Reviewed-by: Torsten Duwe <duwe@suse.de>
> Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
> Tested-by: Kamalesh Babulal <kamalesh@linux.vnet.ibm.com>

Series applied to powerpc next.

https://git.kernel.org/powerpc/c/a5cab83cd3d2d75d3893276cb5

cheers

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#1357733 — Re: [v3,1/8] powerpc: Create a helper for getting the kernel toc value

FromJiri Kosina <jikos@kernel.org>
Date2016-03-15 02:30 +0100
SubjectRe: [v3,1/8] powerpc: Create a helper for getting the kernel toc value
Message-ID<rcLY6-3nY-9@gated-at.bofh.it>
In reply to#1357089
On Mon, 14 Mar 2016, Michael Ellerman wrote:

> > Move the logic to work out the kernel toc pointer into a header. This is
> > a good cleanup, and also means we can use it elsewhere in future.
> > 
> > Reviewed-by: Kamalesh Babulal <kamalesh@linux.vnet.ibm.com>
> > Reviewed-by: Torsten Duwe <duwe@suse.de>
> > Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
> > Tested-by: Kamalesh Babulal <kamalesh@linux.vnet.ibm.com>
> 
> Series applied to powerpc next.
> 
> https://git.kernel.org/powerpc/c/a5cab83cd3d2d75d3893276cb5

Thanks Michael; this is an excellent basis for ppc live patching, but FYI 
I am not merging that one to my tree just yet.

The solution (*) for functions with non-trivial argument list is not there 
yet, and it's my requirement for this to be taken care of in a way that's 
not prone to easily-done human errors on the patch-producer side.

(*) both "making it work" or "making it so broken that it's guaranteed 
    that noone would ever produce a patch that brings the kernel down" is 
    okay, but I really don't feel that just documenting the limitation is
    sufficient and safe in this case; kudos to Torsten here for
    idenfitfying the problem before it actually became The Problem

Thanks,

-- 
Jiri Kosina
SUSE Labs

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#1358800 — Re: [v3,1/8] powerpc: Create a helper for getting the kernel toc value

FromMichael Ellerman <mpe@ellerman.id.au>
Date2016-03-16 11:30 +0100
SubjectRe: [v3,1/8] powerpc: Create a helper for getting the kernel toc value
Message-ID<rdgSe-7Ep-11@gated-at.bofh.it>
In reply to#1357733
On Tue, 2016-03-15 at 02:27 +0100, Jiri Kosina wrote:
> On Mon, 14 Mar 2016, Michael Ellerman wrote:
>
> > > Move the logic to work out the kernel toc pointer into a header. This is
> > > a good cleanup, and also means we can use it elsewhere in future.
> > >
> > > Reviewed-by: Kamalesh Babulal <kamalesh@linux.vnet.ibm.com>
> > > Reviewed-by: Torsten Duwe <duwe@suse.de>
> > > Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
> > > Tested-by: Kamalesh Babulal <kamalesh@linux.vnet.ibm.com>
> >
> > Series applied to powerpc next.
> >
> > https://git.kernel.org/powerpc/c/a5cab83cd3d2d75d3893276cb5
>
> Thanks Michael; this is an excellent basis for ppc live patching, but FYI
> I am not merging that one to my tree just yet.

Yeah OK.

> The solution (*) for functions with non-trivial argument list is not there
> yet, and it's my requirement for this to be taken care of in a way that's
> not prone to easily-done human errors on the patch-producer side.

Sure. I'll try and get something working, though this merge window is not
starting well so I may not get time for a few weeks :)

cheers

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#1359062 — Re: [v3,1/8] powerpc: Create a helper for getting the kernel toc value

FromTorsten Duwe <duwe@lst.de>
Date2016-03-16 16:00 +0100
SubjectRe: [v3,1/8] powerpc: Create a helper for getting the kernel toc value
Message-ID<rdl5w-1RC-7@gated-at.bofh.it>
In reply to#1358800
On Wed, Mar 16, 2016 at 09:23:19PM +1100, Michael Ellerman wrote:
> 
> Sure. I'll try and get something working, though this merge window is not
> starting well so I may not get time for a few weeks :)

Do you already have something in mind?
Can you give us a hint?

	Torsten

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#1359466 — Re: [v3,1/8] powerpc: Create a helper for getting the kernel toc value

FromBalbir Singh <bsingharora@gmail.com>
Date2016-03-17 01:00 +0100
SubjectRe: [v3,1/8] powerpc: Create a helper for getting the kernel toc value
Message-ID<rdtw7-7MK-11@gated-at.bofh.it>
In reply to#1359062

On 17/03/16 01:58, Torsten Duwe wrote:
> On Wed, Mar 16, 2016 at 09:23:19PM +1100, Michael Ellerman wrote:
>> Sure. I'll try and get something working, though this merge window is not
>> starting well so I may not get time for a few weeks :)
> Do you already have something in mind?
> Can you give us a hint?
>
>
We need extra space in the stack, it can be on top of the stack with a pointer in PACA, we could use a fixed set size stack for only LR restore, if required TOC restore, but I think we only need LR space

Balbir Singh.

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#1359470 — Re: [v3,1/8] powerpc: Create a helper for getting the kernel toc value

FromBalbir Singh <bsingharora@gmail.com>
Date2016-03-17 01:00 +0100
SubjectRe: [v3,1/8] powerpc: Create a helper for getting the kernel toc value
Message-ID<rdtw7-7MK-25@gated-at.bofh.it>
In reply to#1357733

On 15/03/16 12:27, Jiri Kosina wrote:
> On Mon, 14 Mar 2016, Michael Ellerman wrote:
>
>>> Move the logic to work out the kernel toc pointer into a header. This is
>>> a good cleanup, and also means we can use it elsewhere in future.
>>>
>>> Reviewed-by: Kamalesh Babulal <kamalesh@linux.vnet.ibm.com>
>>> Reviewed-by: Torsten Duwe <duwe@suse.de>
>>> Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
>>> Tested-by: Kamalesh Babulal <kamalesh@linux.vnet.ibm.com>
>> Series applied to powerpc next.
>>
>> https://git.kernel.org/powerpc/c/a5cab83cd3d2d75d3893276cb5
> Thanks Michael; this is an excellent basis for ppc live patching, but FYI 
> I am not merging that one to my tree just yet.
>
> The solution (*) for functions with non-trivial argument list is not there 
> yet, and it's my requirement for this to be taken care of in a way that's 
> not prone to easily-done human errors on the patch-producer side.
>
> (*) both "making it work" or "making it so broken that it's guaranteed 
>     that noone would ever produce a patch that brings the kernel down" is 
>     okay, but I really don't feel that just documenting the limitation is
>     sufficient and safe in this case; kudos to Torsten here for
>     idenfitfying the problem before it actually became The Problem
To be honest I think my v6 works well, but I don't have complete confidence due to the lack of proper testing. livepatch samples plus some others I wrote and I one Petr wrote all work (calling patched from within patched), but we need more confidence with good tests or an alternative approach that is easier to review and be satisfied with
>
> Thanks,
>

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#1359982 — Re: [v3,1/8] powerpc: Create a helper for getting the kernel toc value

FromTorsten Duwe <duwe@lst.de>
Date2016-03-17 17:00 +0100
SubjectRe: [v3,1/8] powerpc: Create a helper for getting the kernel toc value
Message-ID<rdIv8-Qo-31@gated-at.bofh.it>
In reply to#1359470
On Thu, Mar 17, 2016 at 10:58:42AM +1100, Balbir Singh wrote:
> 
> To be honest I think my v6 works well, but I don't have complete confidence
> due to the lack of proper testing. livepatch samples plus some others I wrote
> and I one Petr wrote all work (calling patched from within patched),

I have outlined a failure scenario for you as a reply to v6 ;)

Question to all: would it be feasible to limit the size of a single module's
.text + TOC to let's say 8MB, and place modules at 10MB granularity? Then it
would be unambiguous: exactly iff the high 40 bits of (TOC-LR) are zero, both
belong to the same module.

	Torsten

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