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1. Virtual Address Translation
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1.1 Hierarchical 4-level per address space page tables
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SPARTAN kernel deploys generic interface for 4-level page tables for these
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architectures: amd64, arm32, ia32, mips32 and ppc32. In this setting, page
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tables are hierarchical and are not shared by address spaces (i.e. one set of
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page tables per address space).
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+-----------------------------------------------------------------------------+
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| PTL0_INDEX | PTL1_INDEX | PTL2_INDEX | PTL3_INDEX | OFFSET |
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+-----------------------------------------------------------------------------+
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+--------+ +--------+ +--------+ +--------+
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| | | | | PTL3 | -----\ | |
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| | | | +--------+ | | |
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| | +--------+ | | | | |
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| | | PTL2 | -----\ | | | | |
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| | +--------+ | | | | | |
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| | | | | | | | +--------+
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+--------+ | | | | | | | FRAME |
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| PTL1 | -----\ | | | | | | +--------+
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+--------+ | | | | | | | | |
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+--------+ \----> +--------+ \----> +--------+ \----> +--------+
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PTL0 Page Table Level 0 (Page Directory)
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PTL1 Page Table Level 1
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PTL2 Page Table Level 2
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PTL3 Page Table Level 3
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PTL0_INDEX Index into PTL0
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PTL1_INDEX Index into PTL1
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PTL2_INDEX Index into PTL2
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PTL3_INDEX Index into PTL3
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VADDR Virtual address for which mapping is looked up
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FRAME Physical address of memory frame to which VADDR is mapped
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On architectures whose hardware has fewer levels, PTL2 and, if need be, PTL1 are
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left out. TLB-only architectures are to define custom format for software page
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1.2 Single global page hash table
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Generic page hash table interface is deployed on 64-bit architectures without
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implied hardware support for hierarchical page tables, i.e. ia64 and sparc64.
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There is only one global page hash table in the system shared by all address
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'malloc' function accepts flags as a second argument. The flags are directly
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passed to the underlying frame_alloc function.
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1) If the flags parameter contains FRAME_ATOMIC, the allocator will not sleep.
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The allocator CAN return NULL, when memory is not directly available.
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The caller MUST check if NULL was not returned
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2) If the flags parameter does not contain FRAME_ATOMIC, the allocator
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will never return NULL, but it CAN sleep indefinitely. The caller
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does not have to check the return value.
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3) The maximum size that can be allocated using malloc is 256K
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Rules 1) and 2) apply to slab_alloc as well. Using SLAB allocator
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to allocate too large values is not recommended.