[PATCH v9 2/10] x86, mm, pat: Change reserve_memtype() for WT

[Toshi Kani <toshi.kani@xxxxxx>]

This patch changes reserve_memtype() to support 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.  reserve_ram_pages_type() is changed to fail
WT and WP requests with -EINVAL since set_page_memtype() is
limited to handle three types, WB, WC and UC-.

Signed-off-by: Toshi Kani <toshi.kani@xxxxxx>
Reviewed-by: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
---
Patch 7/10 enhances set_page_memtype() to support WT.
---
 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 1baa60d..d932b43 100644
--- a/arch/x86/mm/pat.c
+++ b/arch/x86/mm/pat.c
@@ -365,6 +365,8 @@ 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
@@ -376,6 +378,13 @@ 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);
@@ -425,6 +434,7 @@ 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
@@ -442,12 +452,12 @@ 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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