[Crash-utility] x86 remap allocator in kernel 3.0

[Petr Tesarik]

Dne St 11. ledna 2012 15:37:50 Dave Anderson napsal(a):
> ----- Original Message -----
> 
> > Dne St 11. ledna 2012 00:37:50 Petr Tesarik napsal(a):
> > > [...]
> > > I can see now that this is unnecessarily complicated, because the
> > > node_remap_* variables are static arrays of MAX_NUMNODES elements, so I
> > > can get their size from the debuginfo at POST_GDB init and initialize a
> > > machine-specific data type with it. I'll post another patch tomorrow.
> > 
> > And here we go. Tested on my system and seems to work just fine.
> > 
> > Petr Tesarik
> > SUSE Linux
> 
> Hi Petr,
> 
> This looks pretty good to me.  However, just to clarify the
> chicken-and-egg situation here...
> 
> When remap_init() does these 3 readmem() calls, they will pass
> through x86_kvtop_remap() -- which I guess would fail because
> the arrays would still be at least partially uninitialized?:

Hi Dave,

first of all, it's not a real issue, because kernel static data is always 
below the remapped addresses, but I agree, it's ugly and making non-obvious 
assumptions about memory layout. To make things clean, I can simply set 
machdep->machspec->max_numnodes as the last thing, so the loop in 
x86_kvtop_remap() cannot be executed until everything is initialized.

> +	readmem(start_vaddr, KVADDR, ms->remap_start_vaddr,
> +		ms->max_numnodes * sizeof(ulong), "node_remap_start_vaddr",
> +		FAULT_ON_ERROR);
> +	readmem(end_vaddr, KVADDR, ms->remap_end_vaddr,
> +		ms->max_numnodes * sizeof(ulong), "node_remap_end_vaddr",
> +		FAULT_ON_ERROR);
> +	readmem(start_pfn, KVADDR, ms->remap_start_pfn,
> +		ms->max_numnodes * sizeof(ulong), "node_remap_end_vaddr",
> +		FAULT_ON_ERROR);
> 
> To fortify this (and put my mind at ease), can we also set a "remap_state"
> flag in the machdep structure that describes the remap data structures in
> maybe two states:
> 
>   UNINITIALIZED - set at SETUP_ENV time, then cleared in x86_init() before
>                   remap_init() is called

Denoted by max_numnodes == 0

>   NOT_USED      - if remap_init() fails

Denoted by max_numnodes < 0

> Then have x86_kvtop_remap() -- which will get called on every readmem() or
> kvtop() for the rest of time, check for (UNINITIALIZED|NOT_USED), and
> return FALSE immediately if either are set?
> 
> What do you think?

Patch attached.

Petr Tesarik
SUSE Linux
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