[PATCH, RFC 09/62] x86/mm: Preserve KeyID on pte_modify() and pgprot_modify()

["Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>]

An encrypted VMA will have KeyID stored in vma->vm_page_prot. This way
we don't need to do anything special to setup encrypted page table
entries and don't need to reserve space for KeyID in a VMA.

This patch changes _PAGE_CHG_MASK to include KeyID bits. Otherwise they
are going to be stripped from vm_page_prot on the first pgprot_modify().

Define PTE_PFN_MASK_MAX similar to PTE_PFN_MASK but based on
__PHYSICAL_MASK_SHIFT. This way we include whole range of bits
architecturally available for PFN without referencing physical_mask and
mktme_keyid_mask variables.

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
---
 arch/x86/include/asm/pgtable_types.h | 23 ++++++++++++++++++-----
 1 file changed, 18 insertions(+), 5 deletions(-)

diff --git a/arch/x86/include/asm/pgtable_types.h b/arch/x86/include/asm/pgtable_types.h
index d6ff0bbdb394..7d6f68431538 100644
--- a/arch/x86/include/asm/pgtable_types.h
+++ b/arch/x86/include/asm/pgtable_types.h
@@ -117,12 +117,25 @@
 				 _PAGE_ACCESSED | _PAGE_DIRTY)
 
 /*
- * Set of bits not changed in pte_modify.  The pte's
- * protection key is treated like _PAGE_RW, for
- * instance, and is *not* included in this mask since
- * pte_modify() does modify it.
+ * Set of bits not changed in pte_modify.
+ *
+ * The pte's protection key is treated like _PAGE_RW, for instance, and is
+ * *not* included in this mask since pte_modify() does modify it.
+ *
+ * They include the physical address and the memory encryption keyID.
+ * The paddr and the keyID never occupy the same bits at the same time.
+ * But, a given bit might be used for the keyID on one system and used for
+ * the physical address on another. As an optimization, we manage them in
+ * one unit here since their combination always occupies the same hardware
+ * bits. PTE_PFN_MASK_MAX stores combined mask.
+ *
+ * Cast PAGE_MASK to a signed type so that it is sign-extended if
+ * virtual addresses are 32-bits but physical addresses are larger
+ * (ie, 32-bit PAE).
  */
-#define _PAGE_CHG_MASK	(PTE_PFN_MASK | _PAGE_PCD | _PAGE_PWT |		\
+#define PTE_PFN_MASK_MAX \
+	(((signed long)PAGE_MASK) & ((1ULL << __PHYSICAL_MASK_SHIFT) - 1))
+#define _PAGE_CHG_MASK	(PTE_PFN_MASK_MAX | _PAGE_PCD | _PAGE_PWT |		\
 			 _PAGE_SPECIAL | _PAGE_ACCESSED | _PAGE_DIRTY |	\
 			 _PAGE_SOFT_DIRTY | _PAGE_DEVMAP)
 #define _HPAGE_CHG_MASK (_PAGE_CHG_MASK | _PAGE_PSE)
-- 
2.20.1