On Thu, Jun 13, 2013 at 09:02:55PM +0800, Tang Chen wrote:
> From: Yinghai Lu <yinghai@xxxxxxxxxx>
>
> For finding procedure, it would be easy to access initrd in 32bit flat
> mode, as we don't need to setup page table. That is from head_32.S, and
> microcode updating already use this trick.
It'd be really great if you can give a brief explanation of why this
is happening at the beginning of the commit description so that when
someone lands on this commit later on, [s]he can orient oneself. It
doesn't have to be long. Open with something like,
To make NUMA info available early during boot for memory hotplug
support, acpi_initrd_override_find() needs to be used very early
during boot.
and then continue to describe what's happening. It'll make the commit
a lot more approachable to people who just encountered it.
> This patch does the following:
>
> 1. Change acpi_initrd_override_find to use phys to access global variables.
>
> 2. Pass a bool parameter "is_phys" to acpi_initrd_override_find() because
> we cannot tell if it is a pa or a va through the address itself with
> 32bit. Boot loader could load initrd above max_low_pfn.
Do you mean "from 32bit address boundary"? Maybe "from 4G boundary"
is clearer?
>
> 3. Put table_sigs[] on stack, otherwise it is too messy to change string
> array to physaddr and still keep offset calculating correct. The size is
> about 36x4 bytes, and it is small to settle in stack.
>
> 4. Also rewrite the MACRO INVALID_TABLE to be in a do {...} while(0) loop
> so that it is more readable.
The important part is taking "continue" out of it, right?
> +/*
> + * acpi_initrd_override_find() is called from head_32.S and head64.c.
> + * head_32.S calling path is with 32bit flat mode, so we can access
When called from head_32.S, the CPU is in 32bit flat mode and the
kernel virtual address space isn't available yet.
> + * initrd early without setting pagetable or relocating initrd. For
> + * global variables accessing, we need to use phys address instead of
As initrd is in phys_addr, it can be accessed directly; however,
global variables must be accessed by explicitly obtaining their
physical addresses.
> + * kernel virtual address, try to put table_sigs string array in stack,
> + * so avoid switching for it.
Note that table_sigs array is built on stack to avoid such address
translations while accessing its members.
> + * Also don't call printk as it uses global variables.
> + */
> +void __init acpi_initrd_override_find(void *data, size_t size, bool is_phys)
Thanks.
--
tejun
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