mm: Add a vmf_insert_mixed_prot() function

The TTM module today uses a hack to be able to set a different page
protection than struct vm_area_struct::vm_page_prot. To be able to do
this properly, add the needed vm functionality as vmf_insert_mixed_prot().

Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: "Matthew Wilcox (Oracle)" <willy@infradead.org>
Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Cc: Ralph Campbell <rcampbell@nvidia.com>
Cc: "Jérôme Glisse" <jglisse@redhat.com>
Cc: "Christian König" <christian.koenig@amd.com>
Signed-off-by: Thomas Hellstrom <thellstrom@vmware.com>
Acked-by: Christian König <christian.koenig@amd.com>
Acked-by: Michal Hocko <mhocko@suse.com>
Acked-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/include/linux/mm.h b/include/linux/mm.h
index c97ea3b694e65b5b6b48d861d9b98ad388fae6f4..0157d293935f13df1a1d3cf16aafbe1c02b466e4 100644 (file)
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -2533,6 +2533,8 @@ vm_fault_t vmf_insert_pfn_prot(struct vm_area_struct *vma, unsigned long addr,
                        unsigned long pfn, pgprot_t pgprot);
 vm_fault_t vmf_insert_mixed(struct vm_area_struct *vma, unsigned long addr,
                        pfn_t pfn);
+vm_fault_t vmf_insert_mixed_prot(struct vm_area_struct *vma, unsigned long addr,
+                       pfn_t pfn, pgprot_t pgprot);
 vm_fault_t vmf_insert_mixed_mkwrite(struct vm_area_struct *vma,
                unsigned long addr, pfn_t pfn);
 int vm_iomap_memory(struct vm_area_struct *vma, phys_addr_t start, unsigned long len);

diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
index 270aa8fd2800b4234297fa7c27577705f8c24395..e5f0080b4e15b0e8e8558a28aaf5c670fb86ffd4 100644 (file)
--- a/include/linux/mm_types.h
+++ b/include/linux/mm_types.h
@@ -312,7 +312,12 @@ struct vm_area_struct {
        /* Second cache line starts here. */
 
        struct mm_struct *vm_mm;        /* The address space we belong to. */
-       pgprot_t vm_page_prot;          /* Access permissions of this VMA. */
+
+       /*
+        * Access permissions of this VMA.
+        * See vmf_insert_mixed_prot() for discussion.
+        */
+       pgprot_t vm_page_prot;
        unsigned long vm_flags;         /* Flags, see mm.h. */
 
        /*

diff --git a/mm/memory.c b/mm/memory.c
index 606da187d1de904c226d3d53f56d696ab3d8964a..f5e1fe1d5331894c07bae599fd07eed739c732a6 100644 (file)
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -1664,6 +1664,9 @@ static vm_fault_t insert_pfn(struct vm_area_struct *vma, unsigned long addr,
  * vmf_insert_pfn_prot should only be used if using multiple VMAs is
  * impractical.
  *
+ * See vmf_insert_mixed_prot() for a discussion of the implication of using
+ * a value of @pgprot different from that of @vma->vm_page_prot.
+ *
  * Context: Process context.  May allocate using %GFP_KERNEL.
  * Return: vm_fault_t value.
  */
@@ -1737,9 +1740,9 @@ static bool vm_mixed_ok(struct vm_area_struct *vma, pfn_t pfn)
 }
 
 static vm_fault_t __vm_insert_mixed(struct vm_area_struct *vma,
-               unsigned long addr, pfn_t pfn, bool mkwrite)
+               unsigned long addr, pfn_t pfn, pgprot_t pgprot,
+               bool mkwrite)
 {
-       pgprot_t pgprot = vma->vm_page_prot;
        int err;
 
        BUG_ON(!vm_mixed_ok(vma, pfn));
@@ -1782,10 +1785,42 @@ static vm_fault_t __vm_insert_mixed(struct vm_area_struct *vma,
        return VM_FAULT_NOPAGE;
 }
 
+/**
+ * vmf_insert_mixed_prot - insert single pfn into user vma with specified pgprot
+ * @vma: user vma to map to
+ * @addr: target user address of this page
+ * @pfn: source kernel pfn
+ * @pgprot: pgprot flags for the inserted page
+ *
+ * This is exactly like vmf_insert_mixed(), except that it allows drivers to
+ * to override pgprot on a per-page basis.
+ *
+ * Typically this function should be used by drivers to set caching- and
+ * encryption bits different than those of @vma->vm_page_prot, because
+ * the caching- or encryption mode may not be known at mmap() time.
+ * This is ok as long as @vma->vm_page_prot is not used by the core vm
+ * to set caching and encryption bits for those vmas (except for COW pages).
+ * This is ensured by core vm only modifying these page table entries using
+ * functions that don't touch caching- or encryption bits, using pte_modify()
+ * if needed. (See for example mprotect()).
+ * Also when new page-table entries are created, this is only done using the
+ * fault() callback, and never using the value of vma->vm_page_prot,
+ * except for page-table entries that point to anonymous pages as the result
+ * of COW.
+ *
+ * Context: Process context.  May allocate using %GFP_KERNEL.
+ * Return: vm_fault_t value.
+ */
+vm_fault_t vmf_insert_mixed_prot(struct vm_area_struct *vma, unsigned long addr,
+                                pfn_t pfn, pgprot_t pgprot)
+{
+       return __vm_insert_mixed(vma, addr, pfn, pgprot, false);
+}
+
 vm_fault_t vmf_insert_mixed(struct vm_area_struct *vma, unsigned long addr,
                pfn_t pfn)
 {
-       return __vm_insert_mixed(vma, addr, pfn, false);
+       return __vm_insert_mixed(vma, addr, pfn, vma->vm_page_prot, false);
 }
 EXPORT_SYMBOL(vmf_insert_mixed);
 
@@ -1797,7 +1832,7 @@ EXPORT_SYMBOL(vmf_insert_mixed);
 vm_fault_t vmf_insert_mixed_mkwrite(struct vm_area_struct *vma,
                unsigned long addr, pfn_t pfn)
 {
-       return __vm_insert_mixed(vma, addr, pfn, true);
+       return __vm_insert_mixed(vma, addr, pfn, vma->vm_page_prot, true);
 }
 EXPORT_SYMBOL(vmf_insert_mixed_mkwrite);