[PATCH 0/8] powerpc: Kexec fixups and support for booting at 32MB

[Michael Ellerman]

On Sat, 19 Nov 2005 17:44, Milton Miller wrote:
> It's a PowerPC thing that we fiddle with the first 3 pages and that is
> well defined.  It is a kdump thing that the kernel is at 32M, so it
> should reserve 0-32M if it wants that reserved.  The kernel can touch
> reserved memory.   This is based on a discussion I had with Haren
> that the memory given to the kernel would be 0-crash_kernel_end but
> the 0-32M would be reserved.  I guess there is a correctness issue
> if the first 3 pages (4, since we need fwnmi) are not reserved, but
> reserving beyond that to KDUMP_BACKUP_LIMIT is arbitrary.

It's not arbitrary, the fwnmi data area (0x1000 bytes) is fixed (by PAPR) at 
0x7000, so we need to reserve that at least, plus 0-0x3000. We could reserve 
0-0x3000 and 0x7000-0x8000, it struck me as simpler to just grab all of 
0-0x8000. If we do them seperately we'll need to audit the code in between to 
make sure we never use any of it.

ps. When *cough* we support kdump on iSeries we'll need 0x6000 as well.

> In other words, in a pure first-boot high-kernel case, these pages
> couuld be used as normal pages.  The hands-off part is because it
> is dumping the previous kernel.

Only 4 pages, 0x3000-0x7000.

> > [PATCH 7/8] powerpc: Create a trampoline for the fwnmi vectors

> I missed the requirement, and thought this was "register at the
> same place as last time" patch.   I'll withdraw the objection,
> although a comment to this requirement would be nice.

Right ok. There's a comment in the code, did you mean it needs a comment there 
or in the patch?

> >> (2) The secondary hold code could be done as a 64 bit load in the
> >> first 0x100 bytes vs LOADADDR
> >
> > Hmmm, not sure what you mean?
>
> Alternative implementation option: vs LOAD_ADDR(label) do
> t:	.llong <label>
> and
>
> 	ld	4,t at l(0)
>
> Again, just an option to consider, current code is ok, although it
> takes more space and instructions.  (This technique requires t to
> be in the first 2 cache lines so it will be copied down).

I'll think I'll leave it as-is, I don't think it needs to be any trickier.

cheers

-- 
Michael Ellerman
IBM OzLabs

email: michael:ellerman.id.au
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We do not inherit the earth from our ancestors,
we borrow it from our children. - S.M.A.R.T Person
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