docs: move x86 documentation into Documentation/arch/

Move the x86 documentation under Documentation/arch/ as a way of cleaning
up the top-level directory and making the structure of our docs more
closely match the structure of the source directories it describes.

All in-kernel references to the old paths have been updated.

Acked-by: Dave Hansen <dave.hansen@linux.intel.com>
Cc: linux-arch@vger.kernel.org
Cc: x86@kernel.org
Cc: Borislav Petkov <bp@alien8.de>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/lkml/20230315211523.108836-1-corbet@lwn.net/
Signed-off-by: Jonathan Corbet <corbet@lwn.net>

1 files changed, 0 insertions, 240 deletions

diff --git a/Documentation/x86/pat.rst b/Documentation/x86/pat.rst
deleted file mode 100644
index 5d901771016d..000000000000
--- a/Documentation/x86/pat.rst
+++ /dev/null
@@ -1,240 +0,0 @@
-.. SPDX-License-Identifier: GPL-2.0
-
-==========================
-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:
-
-===  ==============
-WB   Write-back
-UC   Uncached
-WC   Write-combined
-WT   Write-through
-UC-  Uncached Minus
-===  ==============
-
-
-PAT APIs
-========
-
-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_uc             |    --    |    UC        |       UC         |
-+------------------------+----------+--------------+------------------+
-| ioremap_wc             |    --    |    --        |       WC         |
-+------------------------+----------+--------------+------------------+
-| ioremap_wt             |    --    |    --        |       WT         |
-+------------------------+----------+--------------+------------------+
-| set_memory_uc,         |    UC-   |    --        |       --         |
-| set_memory_wb          |          |              |                  |
-+------------------------+----------+--------------+------------------+
-| set_memory_wc,         |    WC    |    --        |       --         |
-| set_memory_wb          |          |              |                  |
-+------------------------+----------+--------------+------------------+
-| set_memory_wt,         |    WT    |    --        |       --         |
-| 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               |    --    |   WB/WC/UC-  |    WB/WC/UC-     |
-| read-write             |          |              |                  |
-+------------------------+----------+--------------+------------------+
-| /dev/mem               |    --    |    UC-       |       UC-        |
-| mmap SYNC flag         |          |              |                  |
-+------------------------+----------+--------------+------------------+
-| /dev/mem               |    --    |   WB/WC/UC-  |  WB/WC/UC-       |
-| mmap !SYNC flag        |          |              |                  |
-| and                    |          |(from existing|  (from existing  |
-| any alias to this area |          |alias)        |  alias)          |
-+------------------------+----------+--------------+------------------+
-| /dev/mem               |    --    |    WB        |       WB         |
-| mmap !SYNC flag        |          |              |                  |
-| no alias to this area  |          |              |                  |
-| and                    |          |              |                  |
-| MTRR says WB           |          |              |                  |
-+------------------------+----------+--------------+------------------+
-| /dev/mem               |    --    |    --        |       UC-        |
-| mmap !SYNC flag        |          |              |                  |
-| no alias to this area  |          |              |                  |
-| and                    |          |              |                  |
-| MTRR says !WB          |          |              |                  |
-+------------------------+----------+--------------+------------------+
-
-
-Advanced APIs for drivers
-=========================
-
-A. Exporting pages to users with remap_pfn_range, io_remap_pfn_range,
-vmf_insert_pfn.
-
-Drivers wanting to export some pages to userspace do it by using mmap
-interface and a combination of:
-
-  1) pgprot_noncached()
-  2) io_remap_pfn_range() or remap_pfn_range() or vmf_insert_pfn()
-
-With PAT support, a new API pgprot_writecombine is being added. So, drivers can
-continue to use the above sequence, with either pgprot_noncached() or
-pgprot_writecombine() in step 1, followed by step 2.
-
-In addition, step 2 internally tracks the region as UC or WC in memtype
-list in order to ensure no conflicting mapping.
-
-Note that this set of APIs only works with IO (non RAM) regions. If driver
-wants to export a RAM region, it has to do set_memory_uc() or set_memory_wc()
-as step 0 above and also track the usage of those pages and use set_memory_wb()
-before the page is freed to free pool.
-
-MTRR effects on PAT / non-PAT systems
-=====================================
-
-The following table provides the effects of using write-combining MTRRs when
-using ioremap*() calls on x86 for both non-PAT and PAT systems. Ideally
-mtrr_add() usage will be phased out in favor of arch_phys_wc_add() which will
-be a no-op on PAT enabled systems. The region over which a arch_phys_wc_add()
-is made, should already have been ioremapped with WC attributes or PAT entries,
-this can be done by using ioremap_wc() / set_memory_wc().  Devices which
-combine areas of IO memory desired to remain uncacheable with areas where
-write-combining is desirable should consider use of ioremap_uc() followed by
-set_memory_wc() to white-list effective write-combined areas.  Such use is
-nevertheless discouraged as the effective memory type is considered
-implementation defined, yet this strategy can be used as last resort on devices
-with size-constrained regions where otherwise MTRR write-combining would
-otherwise not be effective.
-::
-
-  ====  =======  ===  =========================  =====================
-  MTRR  Non-PAT  PAT  Linux ioremap value        Effective memory type
-  ====  =======  ===  =========================  =====================
-        PAT                                        Non-PAT |  PAT
-        |PCD                                               |
-        ||PWT                                              |
-        |||                                                |
-  WC    000      WB   _PAGE_CACHE_MODE_WB             WC   |   WC
-  WC    001      WC   _PAGE_CACHE_MODE_WC             WC*  |   WC
-  WC    010      UC-  _PAGE_CACHE_MODE_UC_MINUS       WC*  |   UC
-  WC    011      UC   _PAGE_CACHE_MODE_UC             UC   |   UC
-  ====  =======  ===  =========================  =====================
-
-  (*) denotes implementation defined and is discouraged
-
-.. note:: -- 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|wt] and set_memory_wb should be used in pairs, where driver
-will first make a region uc, wc or wt 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|wt] to set access type for RAM ranges.
-
-
-PAT debugging
-=============
-
-With CONFIG_DEBUG_FS enabled, PAT memtype list can be examined by::
-
-  # mount -t debugfs debugfs /sys/kernel/debug
-  # cat /sys/kernel/debug/x86/pat_memtype_list
-  PAT memtype list:
-  uncached-minus @ 0x7fadf000-0x7fae0000
-  uncached-minus @ 0x7fb19000-0x7fb1a000
-  uncached-minus @ 0x7fb1a000-0x7fb1b000
-  uncached-minus @ 0x7fb1b000-0x7fb1c000
-  uncached-minus @ 0x7fb1c000-0x7fb1d000
-  uncached-minus @ 0x7fb1d000-0x7fb1e000
-  uncached-minus @ 0x7fb1e000-0x7fb25000
-  uncached-minus @ 0x7fb25000-0x7fb26000
-  uncached-minus @ 0x7fb26000-0x7fb27000
-  uncached-minus @ 0x7fb27000-0x7fb28000
-  uncached-minus @ 0x7fb28000-0x7fb2e000
-  uncached-minus @ 0x7fb2e000-0x7fb2f000
-  uncached-minus @ 0x7fb2f000-0x7fb30000
-  uncached-minus @ 0x7fb31000-0x7fb32000
-  uncached-minus @ 0x80000000-0x90000000
-
-This list shows physical address ranges and various PAT settings used to
-access those physical address ranges.
-
-Another, more verbose way of getting PAT related debug messages is with
-"debugpat" boot parameter. With this parameter, various debug messages are
-printed to dmesg log.
-
-PAT Initialization
-==================
-
-The following table describes how PAT is initialized under various
-configurations. The PAT MSR must be updated by Linux in order to support WC
-and WT attributes. Otherwise, the PAT MSR has the value programmed in it
-by the firmware. Note, Xen enables WC attribute in the PAT MSR for guests.
-
- ==== ===== ==========================  =========  =======
- MTRR PAT   Call Sequence               PAT State  PAT MSR
- ==== ===== ==========================  =========  =======
- E    E     MTRR -> PAT init            Enabled    OS
- E    D     MTRR -> PAT init            Disabled    -
- D    E     MTRR -> PAT disable         Disabled   BIOS
- D    D     MTRR -> PAT disable         Disabled    -
- -    np/E  PAT  -> PAT disable         Disabled   BIOS
- -    np/D  PAT  -> PAT disable         Disabled    -
- E    !P/E  MTRR -> PAT init            Disabled   BIOS
- D    !P/E  MTRR -> PAT disable         Disabled   BIOS
- !M   !P/E  MTRR stub -> PAT disable    Disabled   BIOS
- ==== ===== ==========================  =========  =======
-
-  Legend
-
- ========= =======================================
- E         Feature enabled in CPU
- D	   Feature disabled/unsupported in CPU
- np	   "nopat" boot option specified
- !P	   CONFIG_X86_PAT option unset
- !M	   CONFIG_MTRR option unset
- Enabled   PAT state set to enabled
- Disabled  PAT state set to disabled
- OS        PAT initializes PAT MSR with OS setting
- BIOS      PAT keeps PAT MSR with BIOS setting
- ========= =======================================
-