x86: PAT documentation
Documentation about PAT related interfaces, intended usage and memory attribute relationship. Signed-off-by: Venkatesh Pallipadi <venkatesh.pallipadi@intel.com> Signed-off-by: Suresh Siddha <suresh.b.siddha@intel.com> Signed-off-by: Ingo Molnar <mingo@elte.hu>
This commit is contained in:
venkatesh.pallipadi@intel.com
Ingo Molnar
Родитель
7de6a4cdac
Коммит
d27554d874
|
|
@ -0,0 +1,100 @@
|
|||
|
||||
PAT (Page Attribute Table)
|
||||
|
||||
x86 Page Attribute Table (PAT) allows for setting the memory attribute at the
|
||||
page level granularity. PAT is complementary to the MTRR settings which allows
|
||||
for setting of memory types over physical address ranges. However, PAT is
|
||||
more flexible than MTRR due to its capability to set attributes at page level
|
||||
and also due to the fact that there are no hardware limitations on number of
|
||||
such attribute settings allowed. Added flexibility comes with guidelines for
|
||||
not having memory type aliasing for the same physical memory with multiple
|
||||
virtual addresses.
|
||||
|
||||
PAT allows for different types of memory attributes. The most commonly used
|
||||
ones that will be supported at this time are Write-back, Uncached,
|
||||
Write-combined and Uncached Minus.
|
||||
|
||||
There are many different APIs in the kernel that allows setting of memory
|
||||
attributes at the page level. In order to avoid aliasing, these interfaces
|
||||
should be used thoughtfully. Below is a table of interfaces available,
|
||||
their intended usage and their memory attribute relationships. Internally,
|
||||
these APIs use a reserve_memtype()/free_memtype() interface on the physical
|
||||
address range to avoid any aliasing.
|
||||
|
||||
|
||||
-------------------------------------------------------------------
|
||||
API | RAM | ACPI,... | Reserved/Holes |
|
||||
-----------------------|----------|------------|------------------|
|
||||
| | | |
|
||||
ioremap | -- | UC | UC |
|
||||
| | | |
|
||||
ioremap_cache | -- | WB | WB |
|
||||
| | | |
|
||||
ioremap_nocache | -- | UC | UC |
|
||||
| | | |
|
||||
ioremap_wc | -- | -- | WC |
|
||||
| | | |
|
||||
set_memory_uc | UC | -- | -- |
|
||||
set_memory_wb | | | |
|
||||
| | | |
|
||||
set_memory_wc | WC | -- | -- |
|
||||
set_memory_wb | | | |
|
||||
| | | |
|
||||
pci sysfs resource | -- | -- | UC |
|
||||
| | | |
|
||||
pci sysfs resource_wc | -- | -- | WC |
|
||||
is IORESOURCE_PREFETCH| | | |
|
||||
| | | |
|
||||
pci proc | -- | -- | UC |
|
||||
!PCIIOC_WRITE_COMBINE | | | |
|
||||
| | | |
|
||||
pci proc | -- | -- | WC |
|
||||
PCIIOC_WRITE_COMBINE | | | |
|
||||
| | | |
|
||||
/dev/mem | -- | UC | UC |
|
||||
read-write | | | |
|
||||
| | | |
|
||||
/dev/mem | -- | UC | UC |
|
||||
mmap SYNC flag | | | |
|
||||
| | | |
|
||||
/dev/mem | -- | WB/WC/UC | WB/WC/UC |
|
||||
mmap !SYNC flag | |(from exist-| (from exist- |
|
||||
and | | ing alias)| ing alias) |
|
||||
any alias to this area| | | |
|
||||
| | | |
|
||||
/dev/mem | -- | WB | WB |
|
||||
mmap !SYNC flag | | | |
|
||||
no alias to this area | | | |
|
||||
and | | | |
|
||||
MTRR says WB | | | |
|
||||
| | | |
|
||||
/dev/mem | -- | -- | UC_MINUS |
|
||||
mmap !SYNC flag | | | |
|
||||
no alias to this area | | | |
|
||||
and | | | |
|
||||
MTRR says !WB | | | |
|
||||
| | | |
|
||||
-------------------------------------------------------------------
|
||||
|
||||
Notes:
|
||||
|
||||
-- in the above table mean "Not suggested usage for the API". Some of the --'s
|
||||
are strictly enforced by the kernel. Some others are not really enforced
|
||||
today, but may be enforced in future.
|
||||
|
||||
For ioremap and pci access through /sys or /proc - The actual type returned
|
||||
can be more restrictive, in case of any existing aliasing for that address.
|
||||
For example: If there is an existing uncached mapping, a new ioremap_wc can
|
||||
return uncached mapping in place of write-combine requested.
|
||||
|
||||
set_memory_[uc|wc] and set_memory_wb should be used in pairs, where driver will
|
||||
first make a region uc or wc and switch it back to wb after use.
|
||||
|
||||
Over time writes to /proc/mtrr will be deprecated in favor of using PAT based
|
||||
interfaces. Users writing to /proc/mtrr are suggested to use above interfaces.
|
||||
|
||||
Drivers should use ioremap_[uc|wc] to access PCI BARs with [uc|wc] access
|
||||
types.
|
||||
|
||||
Drivers should use set_memory_[uc|wc] to set access type for RAM ranges.
|
||||
|
||||
Загрузка…
Ссылка в новой задаче