Documentation/ia64/aliasing.rst

2 Memory Attribute Aliasing on IA-64
10 Memory Attributes
13     Itanium supports several attributes for virtual memory references.
19         WB		Write-back (cacheable)
21 	WC		Write-coalescing
24     System memory typically uses the WB attribute.  The UC attribute is
25     used for memory-mapped I/O devices.  The WC attribute is uncacheable
34     support either WB or UC access to main memory, while others support
37 Memory Map
40     Platform firmware describes the physical memory map and the
41     supported attributes for each region.  At boot-time, the kernel uses
42     the EFI GetMemoryMap() interface.  ACPI can also describe memory
53     memory Linux is actually using and the attribute for each region.
54     This contains only system memory; it does not contain MMIO space.
57     memory described by the efi_memmap.  Linux/ia64 can't use all memory
62     boot-time information is required for kexec.
75     Therefore, kern_memmap contains only full granule-sized regions that
89     homogeneous with respect to memory attributes.
97 ----------------
106 	an attribute reported as being supported in the EFI memory map.
108 	Since the EFI memory map does not describe MMIO on some
112 -----------------------------------------
127 ------------------------------
130 	may not be requested as using the WC attribute.
132 	If WC is requested, and the region in kern_memmap is either WC
133 	or UC, and the EFI memory map designates the region as WC, then
134 	the WC mapping is allowed.
140 ----------------------
150 	registers typically can be accessed only with four-byte or
151 	eight-byte accesses, and the copy_from_user() path doesn't allow
155 ---------
162 	If the EFI memory map reports that the entire granule supports
166 	If the granule contains non-WB memory, but we can cover the
176 --------------------------------------------------------------------
178       The EFI memory map may not report these MMIO regions.
181       when the EFI memory map is incomplete, every /dev/mem mmap must
183       on whether the region is in kern_memmap or the EFI memory map.
185 mmap of 0x0-0x9FFFF /dev/mem by "hwinfo" on HP sx1000 with VGA enabled
186 ----------------------------------------------------------------------
188       The EFI memory map reports the following attributes:
191         0x00000-0x9FFFF WB only
192         0xA0000-0xBFFFF UC only (VGA frame buffer)
193         0xC0000-0xFFFFF WB only
200       which uses a granule-sized UC mapping.  This granule will cover some
201       WB-only memory, but since UC is non-speculative, the processor will
202       never generate an uncacheable reference to the WB-only areas unless
205 mmap of 0x0-0xFFFFF legacy_mem by "X"
206 -------------------------------------
208       If the EFI memory map reports that the entire range supports the
214       machines with VGA enabled), we must fail the mmap because there's no
221 mmap of 0xA0000-0xBFFFF legacy_mem by "X" on HP sx1000 with VGA disabled
222 ------------------------------------------------------------------------
224       The EFI memory map reports the following attributes::
226         0x00000-0xFFFFF WB only (no VGA MMIO hole)
232 ----------------------------