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Subject[PATCH v5 1/2] mm: Add a vmf_insert_mixed_prot() function
Date
From: Thomas Hellstrom <thellstrom@vmware.com>

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>
---
include/linux/mm.h | 2 ++
include/linux/mm_types.h | 7 ++++++-
mm/memory.c | 43 ++++++++++++++++++++++++++++++++++++----
3 files changed, 47 insertions(+), 5 deletions(-)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index cc292273e6ba..29575d3c1e47 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -2548,6 +2548,8 @@ 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 2222fa795284..aff6cdc784e0 100644
--- a/include/linux/mm_types.h
+++ b/include/linux/mm_types.h
@@ -307,7 +307,12 @@ 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 b1ca51a079f2..269a8a871e83 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -1646,6 +1646,9 @@ 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.
*/
@@ -1719,9 +1722,9 @@ 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));
@@ -1764,10 +1767,42 @@ 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);

@@ -1779,7 +1814,7 @@ 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);

--
2.21.0
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