[PATCH v5 1/2] x86/mm: add a function to check if a pfn is UC/UC-

[Haozhong Zhang <haozhong.zhang@xxxxxxxxx>]

It will be used by KVM to check whether a pfn should be
mapped to guest as UC.

Signed-off-by: Haozhong Zhang <haozhong.zhang@xxxxxxxxx>
---
 arch/x86/include/asm/pat.h |  2 ++
 arch/x86/mm/pat.c          | 16 ++++++++++++++++
 2 files changed, 18 insertions(+)

diff --git a/arch/x86/include/asm/pat.h b/arch/x86/include/asm/pat.h
index fffb2794dd89..fabb0cf00e77 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_or_uc_minus(unsigned long pfn);
+
 #endif /* _ASM_X86_PAT_H */
diff --git a/arch/x86/mm/pat.c b/arch/x86/mm/pat.c
index fe7d57a8fb60..e1282dd4eeb8 100644
--- a/arch/x86/mm/pat.c
+++ b/arch/x86/mm/pat.c
@@ -677,6 +677,22 @@ static enum page_cache_mode lookup_memtype(u64 paddr)
 	return rettype;
 }
 
+/**
+ * Check with PAT whether the memory type of a pfn is UC or UC-.
+ *
+ * Only to be called when PAT is enabled.
+ *
+ * Returns true, if the memory type of @pfn is UC or UC-.
+ * Otherwise, returns false.
+ */
+bool pat_pfn_is_uc_or_uc_minus(unsigned long pfn)
+{
+	enum page_cache_mode cm = lookup_memtype(PFN_PHYS(pfn));
+
+	return cm == _PAGE_CACHE_MODE_UC || cm == _PAGE_CACHE_MODE_UC_MINUS;
+}
+EXPORT_SYMBOL_GPL(pat_pfn_is_uc_or_uc_minus);
+
 /**
  * io_reserve_memtype - Request a memory type mapping for a region of memory
  * @start: start (physical address) of the region
-- 
2.14.1