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 -- To unsubscribe from this list: send the line "unsubscribe linux-doc" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html