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Subject[PATCH v6 2/7] x86, mm, pat: Change reserve_memtype() to handle WT
Date
This patch changes reserve_memtype() to handle the WT cache mode
with PAT. When PAT is not enabled, WB and UC- are the only types
supported.

When a target range is in RAM, reserve_ram_pages_type() verifies
the requested type. In this case, WT and WP requests fail with
-EINVAL and UC gets redirected to UC- since set_page_memtype() is
limited to handle three types, WB, WC and UC-.

Signed-off-by: Toshi Kani <toshi.kani@hp.com>
Reviewed-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
---
arch/x86/mm/pat.c | 18 ++++++++++++++----
1 file changed, 14 insertions(+), 4 deletions(-)

diff --git a/arch/x86/mm/pat.c b/arch/x86/mm/pat.c
index 0f0be47..5552384 100644
--- a/arch/x86/mm/pat.c
+++ b/arch/x86/mm/pat.c
@@ -360,6 +360,8 @@ static int pat_pagerange_is_ram(resource_size_t start, resource_size_t end)

/*
* For RAM pages, we use page flags to mark the pages with appropriate type.
+ * The page flags are limited to three types, WB, WC and UC-.
+ * WT and WP requests fail with -EINVAL, and UC gets redirected to UC-.
* Here we do two pass:
* - Find the memtype of all the pages in the range, look for any conflicts
* - In case of no conflicts, set the new memtype for pages in the range
@@ -371,6 +373,13 @@ static int reserve_ram_pages_type(u64 start, u64 end,
struct page *page;
u64 pfn;

+ if ((req_type == _PAGE_CACHE_MODE_WT) ||
+ (req_type == _PAGE_CACHE_MODE_WP)) {
+ if (new_type)
+ *new_type = _PAGE_CACHE_MODE_UC_MINUS;
+ return -EINVAL;
+ }
+
if (req_type == _PAGE_CACHE_MODE_UC) {
/* We do not support strong UC */
WARN_ON_ONCE(1);
@@ -420,6 +429,7 @@ static int free_ram_pages_type(u64 start, u64 end)
* - _PAGE_CACHE_MODE_WC
* - _PAGE_CACHE_MODE_UC_MINUS
* - _PAGE_CACHE_MODE_UC
+ * - _PAGE_CACHE_MODE_WT
*
* If new_type is NULL, function will return an error if it cannot reserve the
* region with req_type. If new_type is non-NULL, function will return
@@ -437,12 +447,12 @@ int reserve_memtype(u64 start, u64 end, enum page_cache_mode req_type,
BUG_ON(start >= end); /* end is exclusive */

if (!pat_enabled) {
- /* This is identical to page table setting without PAT */
+ /* WB and UC- are the only types supported without PAT */
if (new_type) {
- if (req_type == _PAGE_CACHE_MODE_WC)
- *new_type = _PAGE_CACHE_MODE_UC_MINUS;
+ if (req_type == _PAGE_CACHE_MODE_WB)
+ *new_type = _PAGE_CACHE_MODE_WB;
else
- *new_type = req_type;
+ *new_type = _PAGE_CACHE_MODE_UC_MINUS;
}
return 0;
}

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