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-rw-r--r--arch/x86/pci/i386.c9
1 files changed, 9 insertions, 0 deletions
diff --git a/arch/x86/pci/i386.c b/arch/x86/pci/i386.c
index a70a85d..52e656f 100644
--- a/arch/x86/pci/i386.c
+++ b/arch/x86/pci/i386.c
@@ -280,6 +280,15 @@ int pci_mmap_page_range(struct pci_dev *dev, struct vm_area_struct *vma,
return -EINVAL;
prot = pgprot_val(vma->vm_page_prot);
+
+ /*
+ * Return error if pat is not enabled and write_combine is requested.
+ * Caller can followup with UC MINUS request and add a WC mtrr if there
+ * is a free mtrr slot.
+ */
+ if (!pat_enabled && write_combine)
+ return -EINVAL;
+
if (pat_enabled && write_combine)
prot |= _PAGE_CACHE_WC;
else if (pat_enabled || boot_cpu_data.x86 > 3)
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