[PATCH v3 1/3] x86/mm: add function to check if a pfn is UC/UC-

[Haozhong Zhang]

pat_pfn_is_uc(pfn) is added and will be used by KVM to check whether
the memory type of a host pfn is UC/UC-.

Signed-off-by: Haozhong Zhang <haozhong.zhang@xxxxxxxxx>
---
 arch/x86/include/asm/pat.h |  2 ++
 arch/x86/mm/pat.c          | 14 ++++++++++++++
 2 files changed, 16 insertions(+)

diff --git a/arch/x86/include/asm/pat.h b/arch/x86/include/asm/pat.h
index fffb2794dd89..4027d9fb10a8 100644
--- a/arch/x86/include/asm/pat.h
+++ b/arch/x86/include/asm/pat.h
@@ -21,4 +21,6 @@ int io_reserve_memtype(resource_size_t start, resource_size_t end,
 
 void io_free_memtype(resource_size_t start, resource_size_t end);
 
+bool pat_pfn_is_uc(pfn_t pfn);
+
 #endif /* _ASM_X86_PAT_H */
diff --git a/arch/x86/mm/pat.c b/arch/x86/mm/pat.c
index fe7d57a8fb60..71fe9c29727e 100644
--- a/arch/x86/mm/pat.c
+++ b/arch/x86/mm/pat.c
@@ -677,6 +677,20 @@ static enum page_cache_mode lookup_memtype(u64 paddr)
 	return rettype;
 }
 
+/**
+ * Check whether the memory type of a pfn is UC or UC-. The result is
+ * valid only when PAT is enabled.
+ *
+ * Returns true if it is; otherwise, returns false.
+ */
+bool pat_pfn_is_uc(pfn_t pfn)
+{
+	enum page_cache_mode cm = lookup_memtype(pfn_t_to_phys(pfn));
+
+	return cm == _PAGE_CACHE_MODE_UC || cm == _PAGE_CACHE_MODE_UC_MINUS;
+}
+EXPORT_SYMBOL_GPL(pat_pfn_is_uc);
+
 /**
  * io_reserve_memtype - Request a memory type mapping for a region of memory
  * @start: start (physical address) of the region
-- 
2.14.1