Messages in this thread Patch in this message | ![/](/images/icornerl.gif) | | From | Yan Zhao <> | Subject | [PATCH] Documentation: x86: Correct effective memory type for MTRR=WC and PAT=UC- | Date | Mon, 6 Nov 2023 12:53:56 +0800 |
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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@kernel.org [1] Cc: Sean Christopherson <seanjc@google.com> Reviewed-by: Kai Huang <kai.huang@intel.com> Signed-off-by: Yan Zhao <yan.y.zhao@intel.com> --- 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
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