Correct effective memory type for a WC MTRR on a region with a PAT entry
UC- from UC to WC.
As per Intel SDM section "Selecting Memory Types for Pentium III and More
Recent Processor Families", table "Effective Page-Level Memory Types for
Pentium III and More Recent Processor Families",
================ =============== =====================
MTRR Memory Type PAT Entry Value Effective Memory Type
================ =============== =====================
WC UC- WC
the effect of a WC MTRR on a region with a PAT entry UC- will be WC.
There's a previous attempt to fix this issue at [1], but not sure why the
patch got lost.
Fixes: 2f9e897353fc ("x86/mm/mtrr, pat: Document Write Combining MTRR type effects on PAT / non-PAT pages").
Link: https://lore.kernel.org/all/1457131501-14855-1-git-send-email-mcgrof@xxxxxxxxxx [1]
Cc: Sean Christopherson <seanjc@xxxxxxxxxx>
Reviewed-by: Kai Huang <kai.huang@xxxxxxxxx>
Signed-off-by: Yan Zhao <yan.y.zhao@xxxxxxxxx>
---
Documentation/arch/x86/pat.rst | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/Documentation/arch/x86/pat.rst b/Documentation/arch/x86/pat.rst
index 5d901771016d..414129efa316 100644
--- a/Documentation/arch/x86/pat.rst
+++ b/Documentation/arch/x86/pat.rst
@@ -138,19 +138,19 @@ 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 010 UC- _PAGE_CACHE_MODE_UC_MINUS WC* | WC
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.
base-commit: 1aabbc532413ced293952f8e149ad0a607d6e470
--
2.17.1
