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94fd522069
As per description in mm/memory_hotplug.c platforms should define arch_get_mappable_range() that provides maximum possible addressable physical memory range for which the linear mapping could be created. The current implementation uses VMEM_MAX_PHYS macro as the maximum mappable physical address and it is simply a cast to vmemmap. Since the address is in physical address space the natural upper limit of MAX_PHYSMEM_BITS is honoured: vmemmap_start = min(vmemmap_start, 1UL << MAX_PHYSMEM_BITS); Further, to make sure the identity mapping would not overlay with vmemmap, the size of identity mapping could be stripped like this: ident_map_size = min(ident_map_size, vmemmap_start); Similarily, any other memory that could be added (e.g DCSS segment) should not overlay with vmemmap as well and that is prevented by using vmemmap (VMEM_MAX_PHYS macro) as the upper limit. However, while the use of VMEM_MAX_PHYS brings the desired result it actually poses two issues: 1. As described, vmemmap is handled as a physical address, although it is actually a pointer to struct page in virtual address space. 2. As vmemmap is a virtual address it could have been located anywhere in the virtual address space. However, the desired necessity to honour MAX_PHYSMEM_BITS limit prevents that. Rework arch_get_mappable_range() callback in a way it does not use VMEM_MAX_PHYS macro and does not confuse the notion of virtual vs physical address spacees as result. That paves the way for moving vmemmap elsewhere and optimizing the virtual address space layout. Introduce max_mappable preserved boot variable and let function setup_kernel_memory_layout() set it up. As result, the rest of the code is does not need to know the virtual memory layout specifics. Reviewed-by: Heiko Carstens <hca@linux.ibm.com> Signed-off-by: Alexander Gordeev <agordeev@linux.ibm.com> Signed-off-by: Heiko Carstens <hca@linux.ibm.com> |
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Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.