Messages in this thread | | | Date | Thu, 20 Jul 2000 13:06:21 -0500 | From | Timur Tabi <> | Subject | phys-to-virt kernel mapping and ioremap() |
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I'm studying the code for __ioremap and I'm confused by something.
The phys_to_virt and virt_to_phys macros are very simple. Basically, in kernel space, the virtual address is an offset of the physical address, so it's very simple.
__ioremap is supposed to take high PCI memory and map it to kernel space. However, __ioremap() calls get_vm_area() which then calls kmalloc(), which allocates some memory from the heap. Then remap_area_pages() is called, and that uses the three-level page tables to map the memory allocated by kmalloc to the PCI memory.
And that's where I'm confused. Particularly:
1) Doesn't this mapping break the phys_to_virt and virt_to_phys macros?
2) kmalloc takes real physical memory from the kernel heap. But then the virtual addresses are remapped to other physical memory. What happens to the physical memory that kmalloc allocated? Why isn't it freed?
-- Timur Tabi - ttabi@interactivesi.com Interactive Silicon - http://www.interactivesi.com
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