[Xen-devel] [PATCH] x86: define arch_vm_get_page_prot to set _PAGE_IOMAP on VM_IO vmas

[Jeremy Fitzhardinge <jeremy@xxxxxxxx>]

Set _PAGE_IOMAP in ptes mapping a VM_IO vma.  This says that the mapping
is of a real piece of physical hardware, and not just system memory.

Xen, in particular, uses to this to inhibit the normal pfn->mfn conversion
that would normally happen - in other words, treat the address directly
as a machine physical address without converting it from pseudo-physical.

[ Impact: make VM_IO mappings map the right thing under Xen ]

Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@xxxxxxxxxx>

diff --git a/arch/x86/include/asm/pgtable.h b/arch/x86/include/asm/pgtable.h
index 3cc06e3..4595ae2 100644
--- a/arch/x86/include/asm/pgtable.h
+++ b/arch/x86/include/asm/pgtable.h
@@ -394,6 +394,9 @@ static inline unsigned long pages_to_mb(unsigned long npg)
 #define io_remap_pfn_range(vma, vaddr, pfn, size, prot)        \
        remap_pfn_range(vma, vaddr, pfn, size, prot)
 
+#define arch_vm_get_page_prot arch_vm_get_page_prot
+extern pgprot_t arch_vm_get_page_prot(unsigned vm_flags);
+
 #if PAGETABLE_LEVELS > 2
 static inline int pud_none(pud_t pud)
 {
diff --git a/arch/x86/mm/pgtable.c b/arch/x86/mm/pgtable.c
index 8e43bdd..e68aea6 100644
--- a/arch/x86/mm/pgtable.c
+++ b/arch/x86/mm/pgtable.c
@@ -6,6 +6,16 @@
 
 #define PGALLOC_GFP GFP_KERNEL | __GFP_NOTRACK | __GFP_REPEAT | __GFP_ZERO
 
+pgprot_t arch_vm_get_page_prot(unsigned vm_flags)
+{
+       pgprot_t ret = __pgprot(0);
+
+       if (vm_flags & VM_IO)
+               ret = __pgprot(_PAGE_IOMAP);
+
+       return ret;
+}
+
 pte_t *pte_alloc_one_kernel(struct mm_struct *mm, unsigned long address)
 {
        return (pte_t *)__get_free_page(PGALLOC_GFP);

Attachment: define-arch_vm_get_page_prot.patch
Description: Text document

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