On Sat, Oct 31, 2009 at 10:54 PM, Zhu Yanhai <zhu.yanhai@xxxxxxxxx> wrote:
Page table directory is pointed by CR3 register not CR0. Just FYI.
CR0 has PE bit to enable paging.
2009/10/30 shailesh jain <coolworldofshail@xxxxxxxxx>:
> a) __pa(kaddr) : Translates kernel virtual address to physical address,the macro is used by programmers, not by X86 CPU. CPU only knows the
> which is just arithmetic operation subtracting PAGE_OFFSET from kaddr.
>
>
> b) #define virt_to_page(kaddr) (mem_map + (__pa(kaddr) >> PAGE_SHIFT))
> above macro is giving you struct page for a corresponding virtual address.
>
> c) linear address to physical address translation is done by x86 processor
> (32 but without PAE) by doing traversal pgd->pte->page_phys_addr. OS sets up
> this entries and processor uses it.
>
> Yes, above macro is not for ZONE_HIGHMEM. Because ZONE_HIGHMEM is not
> directly mapped by kernel.
>
>
> Shailesh Jain
>
> On Fri, Oct 23, 2009 at 2:01 PM, Shameem Ahamed <shameem.ahamed@xxxxxxxxx>
> wrote:
>>
>> Hi Friends,
>>
>> Please help me to figure out some basic concepts in MM.
>>
>> From the books, i learned that VMA to PA translation consists of
>> traversing the full page directory, which consists of Global Directory,
>> Middle Directory and Page Table.
>>
>> I have also read that, VMA to PA translation is done using a macro
>> virt_to_page defined as given below.
>>
>> #define virt_to_page(kaddr) (mem_map + (__pa(kaddr) >> PAGE_SHIFT))
>>
>>
>> If
>> there is a macro, why we need code for traversing all the page
>> directories ?. This macro is a simple math, which points to an index
>> in global mem_map array, which contains all the pages in the system.
>>
page tables pointed by CR0.
Page table directory is pointed by CR3 register not CR0. Just FYI.
CR0 has PE bit to enable paging.
>>Yes
>> So my doubts are,
>> Is the macro only for ZONE_NORMAL (upto 896M, which is directly mapped by
>> kernel) memory pages ?.
>> Is mem_map array contains pages upto ZONE_NORMAL ?No, mem_map contains all physical page frames.
No, page traversing happens for every page frame that CPU wants to
>> Is page traversing happens only for HIGH_MEM ?
visit and can't be found in TLB entries.
The point is page directory contains all page mappings, and the parts
of mapping of ZONE_NORMAL is simple
and they can be described by pa and va macros. But, CPU doesn't know
pa and va marcro, and CPU can only
find pages by page tables.
.
>>
>> Regards,
>> Shameem
>>
>>
>>
>>
>>
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>
>
