[RFC PATCH v4 07/28] x86: Provide general kernel support for memory encryption

Tom Lendacky
2017-02-16T15:43:44Z

Adding general kernel support for memory encryption includes:
- Modify and create some page table macros to include the Secure Memory
Encryption (SME) memory encryption mask
- Modify and create some macros for calculating physical and virtual
memory addresses
- Provide an SME initialization routine to update the protection map with
the memory encryption mask so that it is used by default
- #undef CONFIG_AMD_MEM_ENCRYPT in the compressed boot path

Signed-off-by: Tom Lendacky <thomas.lendacky@amd.com>
---
arch/x86/boot/compressed/pagetable.c | 7 +++++
arch/x86/include/asm/fixmap.h | 7 +++++
arch/x86/include/asm/mem_encrypt.h | 14 +++++++++++
arch/x86/include/asm/page.h | 4 ++-
arch/x86/include/asm/pgtable.h | 26 ++++++++++++++------
arch/x86/include/asm/pgtable_types.h | 45 ++++++++++++++++++++++------------
arch/x86/include/asm/processor.h | 3 ++
arch/x86/kernel/espfix_64.c | 2 +-
arch/x86/kernel/head64.c | 12 ++++++++-
arch/x86/kernel/head_64.S | 18 +++++++-------
arch/x86/mm/kasan_init_64.c | 4 ++-
arch/x86/mm/mem_encrypt.c | 20 +++++++++++++++
arch/x86/mm/pageattr.c | 3 ++
include/asm-generic/pgtable.h | 8 ++++++
14 files changed, 133 insertions(+), 40 deletions(-)

diff --git a/arch/x86/boot/compressed/pagetable.c b/arch/x86/boot/compressed/pagetable.c
index 56589d0..411c443 100644
--- a/arch/x86/boot/compressed/pagetable.c
+++ b/arch/x86/boot/compressed/pagetable.c
@@ -15,6 +15,13 @@
#define __pa(x) ((unsigned long)(x))
#define __va(x) ((void *)((unsigned long)(x)))

+/*
+ * The pgtable.h and mm/ident_map.c includes make use of the SME related
+ * information which is not used in the compressed image support. Un-define
+ * the SME support to avoid any compile and link errors.
+ */
+#undef CONFIG_AMD_MEM_ENCRYPT
+
#include "misc.h"

/* These actually do the work of building the kernel identity maps. */
diff --git a/arch/x86/include/asm/fixmap.h b/arch/x86/include/asm/fixmap.h
index 8554f96..83e91f0 100644
--- a/arch/x86/include/asm/fixmap.h
+++ b/arch/x86/include/asm/fixmap.h
@@ -153,6 +153,13 @@ static inline void __set_fixmap(enum fixed_addresses idx,
}
#endif

+/*
+ * Fixmap settings used with memory encryption
+ * - FIXMAP_PAGE_NOCACHE is used for MMIO so make sure the memory
+ * encryption mask is not part of the page attributes
+ */
+#define FIXMAP_PAGE_NOCACHE PAGE_KERNEL_IO_NOCACHE
+
#include <asm-generic/fixmap.h>

#define __late_set_fixmap(idx, phys, flags) __set_fixmap(idx, phys, flags)
diff --git a/arch/x86/include/asm/mem_encrypt.h b/arch/x86/include/asm/mem_encrypt.h
index ccc53b0..547989d 100644
--- a/arch/x86/include/asm/mem_encrypt.h
+++ b/arch/x86/include/asm/mem_encrypt.h
@@ -15,6 +15,8 @@

#ifndef __ASSEMBLY__

+#include <linux/init.h>
+
#ifdef CONFIG_AMD_MEM_ENCRYPT

extern unsigned long sme_me_mask;
@@ -24,6 +26,11 @@ static inline bool sme_active(void)
return (sme_me_mask) ? true : false;
}

+void __init sme_early_init(void);
+
+#define __sme_pa(x) (__pa((x)) | sme_me_mask)
+#define __sme_pa_nodebug(x) (__pa_nodebug((x)) | sme_me_mask)
+
#else /* !CONFIG_AMD_MEM_ENCRYPT */

#ifndef sme_me_mask
@@ -35,6 +42,13 @@ static inline bool sme_active(void)
}
#endif

+static inline void __init sme_early_init(void)
+{
+}
+
+#define __sme_pa __pa
+#define __sme_pa_nodebug __pa_nodebug
+
#endif /* CONFIG_AMD_MEM_ENCRYPT */

#endif /* __ASSEMBLY__ */
diff --git a/arch/x86/include/asm/page.h b/arch/x86/include/asm/page.h
index cf8f619..b1f7bf6 100644
--- a/arch/x86/include/asm/page.h
+++ b/arch/x86/include/asm/page.h
@@ -15,6 +15,8 @@

#ifndef __ASSEMBLY__

+#include <asm/mem_encrypt.h>
+
struct page;

#include <linux/range.h>
@@ -55,7 +57,7 @@ static inline void copy_user_page(void *to, void *from, unsigned long vaddr,
__phys_addr_symbol(__phys_reloc_hide((unsigned long)(x)))

#ifndef __va
-#define __va(x) ((void *)((unsigned long)(x)+PAGE_OFFSET))
+#define __va(x) ((void *)(((unsigned long)(x) & ~sme_me_mask) + PAGE_OFFSET))
#endif

#define __boot_va(x) __va(x)
diff --git a/arch/x86/include/asm/pgtable.h b/arch/x86/include/asm/pgtable.h
index 2d81161..b41caab 100644
--- a/arch/x86/include/asm/pgtable.h
+++ b/arch/x86/include/asm/pgtable.h
@@ -3,6 +3,7 @@

#include <asm/page.h>
#include <asm/pgtable_types.h>
+#include <asm/mem_encrypt.h>

/*
* Macro to mark a page protection value as UC-
@@ -13,6 +14,12 @@
cachemode2protval(_PAGE_CACHE_MODE_UC_MINUS))) \
: (prot))

+/*
+ * Macros to add or remove encryption attribute
+ */
+#define pgprot_encrypted(prot) __pgprot(pgprot_val(prot) | sme_me_mask)
+#define pgprot_decrypted(prot) __pgprot(pgprot_val(prot) & ~sme_me_mask)
+
#ifndef __ASSEMBLY__
#include <asm/x86_init.h>

@@ -153,17 +160,22 @@ static inline int pte_special(pte_t pte)

static inline unsigned long pte_pfn(pte_t pte)
{
- return (pte_val(pte) & PTE_PFN_MASK) >> PAGE_SHIFT;
+ return (pte_val(pte) & ~sme_me_mask & PTE_PFN_MASK) >> PAGE_SHIFT;
}

static inline unsigned long pmd_pfn(pmd_t pmd)
{
- return (pmd_val(pmd) & pmd_pfn_mask(pmd)) >> PAGE_SHIFT;
+ return (pmd_val(pmd) & ~sme_me_mask & pmd_pfn_mask(pmd)) >> PAGE_SHIFT;
}

static inline unsigned long pud_pfn(pud_t pud)
{
- return (pud_val(pud) & pud_pfn_mask(pud)) >> PAGE_SHIFT;
+ return (pud_val(pud) & ~sme_me_mask & pud_pfn_mask(pud)) >> PAGE_SHIFT;
+}
+
+static inline unsigned long pgd_pfn(pgd_t pgd)
+{
+ return (pgd_val(pgd) & ~sme_me_mask) >> PAGE_SHIFT;
}

#define pte_page(pte) pfn_to_page(pte_pfn(pte))
@@ -563,8 +575,7 @@ static inline unsigned long pmd_page_vaddr(pmd_t pmd)
* Currently stuck as a macro due to indirect forward reference to
* linux/mmzone.h's __section_mem_map_addr() definition:
*/
-#define pmd_page(pmd) \
- pfn_to_page((pmd_val(pmd) & pmd_pfn_mask(pmd)) >> PAGE_SHIFT)
+#define pmd_page(pmd) pfn_to_page(pmd_pfn(pmd))

/*
* the pmd page can be thought of an array like this: pmd_t[PTRS_PER_PMD]
@@ -632,8 +643,7 @@ static inline unsigned long pud_page_vaddr(pud_t pud)
* Currently stuck as a macro due to indirect forward reference to
* linux/mmzone.h's __section_mem_map_addr() definition:
*/
-#define pud_page(pud) \
- pfn_to_page((pud_val(pud) & pud_pfn_mask(pud)) >> PAGE_SHIFT)
+#define pud_page(pud) pfn_to_page(pud_pfn(pud))

/* Find an entry in the second-level page table.. */
static inline pmd_t *pmd_offset(pud_t *pud, unsigned long address)
@@ -673,7 +683,7 @@ static inline unsigned long pgd_page_vaddr(pgd_t pgd)
* Currently stuck as a macro due to indirect forward reference to
* linux/mmzone.h's __section_mem_map_addr() definition:
*/
-#define pgd_page(pgd) pfn_to_page(pgd_val(pgd) >> PAGE_SHIFT)
+#define pgd_page(pgd) pfn_to_page(pgd_pfn(pgd))

/* to find an entry in a page-table-directory. */
static inline unsigned long pud_index(unsigned long address)
diff --git a/arch/x86/include/asm/pgtable_types.h b/arch/x86/include/asm/pgtable_types.h
index 8b4de22..500fc60 100644
--- a/arch/x86/include/asm/pgtable_types.h
+++ b/arch/x86/include/asm/pgtable_types.h
@@ -2,7 +2,9 @@
#define _ASM_X86_PGTABLE_DEFS_H

#include <linux/const.h>
+
#include <asm/page_types.h>
+#include <asm/mem_encrypt.h>

#define FIRST_USER_ADDRESS 0UL

@@ -121,10 +123,10 @@

#define _PAGE_PROTNONE (_AT(pteval_t, 1) << _PAGE_BIT_PROTNONE)

-#define _PAGE_TABLE (_PAGE_PRESENT | _PAGE_RW | _PAGE_USER | \
- _PAGE_ACCESSED | _PAGE_DIRTY)
-#define _KERNPG_TABLE (_PAGE_PRESENT | _PAGE_RW | _PAGE_ACCESSED | \
- _PAGE_DIRTY)
+#define _PAGE_TABLE_NOENC (_PAGE_PRESENT | _PAGE_RW | _PAGE_USER |\
+ _PAGE_ACCESSED | _PAGE_DIRTY)
+#define _KERNPG_TABLE_NOENC (_PAGE_PRESENT | _PAGE_RW | \
+ _PAGE_ACCESSED | _PAGE_DIRTY)

/*
* Set of bits not changed in pte_modify. The pte's
@@ -191,18 +193,29 @@ enum page_cache_mode {
#define __PAGE_KERNEL_IO (__PAGE_KERNEL)
#define __PAGE_KERNEL_IO_NOCACHE (__PAGE_KERNEL_NOCACHE)

-#define PAGE_KERNEL __pgprot(__PAGE_KERNEL)
-#define PAGE_KERNEL_RO __pgprot(__PAGE_KERNEL_RO)
-#define PAGE_KERNEL_EXEC __pgprot(__PAGE_KERNEL_EXEC)
-#define PAGE_KERNEL_RX __pgprot(__PAGE_KERNEL_RX)
-#define PAGE_KERNEL_NOCACHE __pgprot(__PAGE_KERNEL_NOCACHE)
-#define PAGE_KERNEL_LARGE __pgprot(__PAGE_KERNEL_LARGE)
-#define PAGE_KERNEL_LARGE_EXEC __pgprot(__PAGE_KERNEL_LARGE_EXEC)
-#define PAGE_KERNEL_VSYSCALL __pgprot(__PAGE_KERNEL_VSYSCALL)
-#define PAGE_KERNEL_VVAR __pgprot(__PAGE_KERNEL_VVAR)
-
-#define PAGE_KERNEL_IO __pgprot(__PAGE_KERNEL_IO)
-#define PAGE_KERNEL_IO_NOCACHE __pgprot(__PAGE_KERNEL_IO_NOCACHE)
+#ifndef __ASSEMBLY__
+
+#define _PAGE_ENC (_AT(pteval_t, sme_me_mask))
+
+#define _PAGE_TABLE (_PAGE_PRESENT | _PAGE_RW | _PAGE_USER | \
+ _PAGE_ACCESSED | _PAGE_DIRTY | _PAGE_ENC)
+#define _KERNPG_TABLE (_PAGE_PRESENT | _PAGE_RW | _PAGE_ACCESSED | \
+ _PAGE_DIRTY | _PAGE_ENC)
+
+#define PAGE_KERNEL __pgprot(__PAGE_KERNEL | _PAGE_ENC)
+#define PAGE_KERNEL_RO __pgprot(__PAGE_KERNEL_RO | _PAGE_ENC)
+#define PAGE_KERNEL_EXEC __pgprot(__PAGE_KERNEL_EXEC | _PAGE_ENC)
+#define PAGE_KERNEL_RX __pgprot(__PAGE_KERNEL_RX | _PAGE_ENC)
+#define PAGE_KERNEL_NOCACHE __pgprot(__PAGE_KERNEL_NOCACHE | _PAGE_ENC)
+#define PAGE_KERNEL_LARGE __pgprot(__PAGE_KERNEL_LARGE | _PAGE_ENC)
+#define PAGE_KERNEL_LARGE_EXEC __pgprot(__PAGE_KERNEL_LARGE_EXEC | _PAGE_ENC)
+#define PAGE_KERNEL_VSYSCALL __pgprot(__PAGE_KERNEL_VSYSCALL | _PAGE_ENC)
+#define PAGE_KERNEL_VVAR __pgprot(__PAGE_KERNEL_VVAR | _PAGE_ENC)
+
+#define PAGE_KERNEL_IO __pgprot(__PAGE_KERNEL_IO)
+#define PAGE_KERNEL_IO_NOCACHE __pgprot(__PAGE_KERNEL_IO_NOCACHE)
+
+#endif /* __ASSEMBLY__ */

/* xwr */
#define __P000 PAGE_NONE
diff --git a/arch/x86/include/asm/processor.h b/arch/x86/include/asm/processor.h
index e6cfe7b..86da9a4 100644
--- a/arch/x86/include/asm/processor.h
+++ b/arch/x86/include/asm/processor.h
@@ -22,6 +22,7 @@
#include <asm/nops.h>
#include <asm/special_insns.h>
#include <asm/fpu/types.h>
+#include <asm/mem_encrypt.h>

#include <linux/personality.h>
#include <linux/cache.h>
@@ -240,7 +241,7 @@ static inline void native_cpuid(unsigned int *eax, unsigned int *ebx,

static inline void load_cr3(pgd_t *pgdir)
{
- write_cr3(__pa(pgdir));
+ write_cr3(__sme_pa(pgdir));
}

#ifdef CONFIG_X86_32
diff --git a/arch/x86/kernel/espfix_64.c b/arch/x86/kernel/espfix_64.c
index 04f89ca..51566d7 100644
--- a/arch/x86/kernel/espfix_64.c
+++ b/arch/x86/kernel/espfix_64.c
@@ -193,7 +193,7 @@ void init_espfix_ap(int cpu)

pte_p = pte_offset_kernel(&pmd, addr);
stack_page = page_address(alloc_pages_node(node, GFP_KERNEL, 0));
- pte = __pte(__pa(stack_page) | (__PAGE_KERNEL_RO & ptemask));
+ pte = __pte(__pa(stack_page) | ((__PAGE_KERNEL_RO | _PAGE_ENC) & ptemask));
for (n = 0; n < ESPFIX_PTE_CLONES; n++)
set_pte(&pte_p[n*PTE_STRIDE], pte);

diff --git a/arch/x86/kernel/head64.c b/arch/x86/kernel/head64.c
index baa0e7b..182a4c7 100644
--- a/arch/x86/kernel/head64.c
+++ b/arch/x86/kernel/head64.c
@@ -28,6 +28,7 @@
#include <asm/bootparam_utils.h>
#include <asm/microcode.h>
#include <asm/kasan.h>
+#include <asm/mem_encrypt.h>

/*
* Manage page tables very early on.
@@ -42,7 +43,7 @@ static void __init reset_early_page_tables(void)
{
memset(early_level4_pgt, 0, sizeof(pgd_t)*(PTRS_PER_PGD-1));
next_early_pgt = 0;
- write_cr3(__pa_nodebug(early_level4_pgt));
+ write_cr3(__sme_pa_nodebug(early_level4_pgt));
}

/* Create a new PMD entry */
@@ -54,7 +55,7 @@ int __init early_make_pgtable(unsigned long address)
pmdval_t pmd, *pmd_p;

/* Invalid address or early pgt is done ? */
- if (physaddr >= MAXMEM || read_cr3() != __pa_nodebug(early_level4_pgt))
+ if (physaddr >= MAXMEM || read_cr3() != __sme_pa_nodebug(early_level4_pgt))
return -1;

again:
@@ -157,6 +158,13 @@ asmlinkage __visible void __init x86_64_start_kernel(char * real_mode_data)

clear_page(init_level4_pgt);

+ /*
+ * SME support may update early_pmd_flags to include the memory
+ * encryption mask, so it needs to be called before anything
+ * that may generate a page fault.
+ */
+ sme_early_init();
+
kasan_early_init();

for (i = 0; i < NUM_EXCEPTION_VECTORS; i++)
diff --git a/arch/x86/kernel/head_64.S b/arch/x86/kernel/head_64.S
index 4f8201b..edd2f14 100644
--- a/arch/x86/kernel/head_64.S
+++ b/arch/x86/kernel/head_64.S
@@ -129,7 +129,7 @@ startup_64:
movq %rdi, %rax
shrq $PGDIR_SHIFT, %rax

- leaq (PAGE_SIZE + _KERNPG_TABLE)(%rbx), %rdx
+ leaq (PAGE_SIZE + _KERNPG_TABLE_NOENC)(%rbx), %rdx
addq %r12, %rdx
movq %rdx, 0(%rbx,%rax,8)
movq %rdx, 8(%rbx,%rax,8)
@@ -463,7 +463,7 @@ GLOBAL(name)
__INITDATA
NEXT_PAGE(early_level4_pgt)
.fill 511,8,0
- .quad level3_kernel_pgt - __START_KERNEL_map + _PAGE_TABLE
+ .quad level3_kernel_pgt - __START_KERNEL_map + _PAGE_TABLE_NOENC

NEXT_PAGE(early_dynamic_pgts)
.fill 512*EARLY_DYNAMIC_PAGE_TABLES,8,0
@@ -475,15 +475,15 @@ NEXT_PAGE(init_level4_pgt)
.fill 512,8,0
#else
NEXT_PAGE(init_level4_pgt)
- .quad level3_ident_pgt - __START_KERNEL_map + _KERNPG_TABLE
+ .quad level3_ident_pgt - __START_KERNEL_map + _KERNPG_TABLE_NOENC
.org init_level4_pgt + L4_PAGE_OFFSET*8, 0
- .quad level3_ident_pgt - __START_KERNEL_map + _KERNPG_TABLE
+ .quad level3_ident_pgt - __START_KERNEL_map + _KERNPG_TABLE_NOENC
.org init_level4_pgt + L4_START_KERNEL*8, 0
/* (2^48-(2*1024*1024*1024))/(2^39) = 511 */
- .quad level3_kernel_pgt - __START_KERNEL_map + _PAGE_TABLE
+ .quad level3_kernel_pgt - __START_KERNEL_map + _PAGE_TABLE_NOENC

NEXT_PAGE(level3_ident_pgt)
- .quad level2_ident_pgt - __START_KERNEL_map + _KERNPG_TABLE
+ .quad level2_ident_pgt - __START_KERNEL_map + _KERNPG_TABLE_NOENC
.fill 511, 8, 0
NEXT_PAGE(level2_ident_pgt)
/* Since I easily can, map the first 1G.
@@ -495,8 +495,8 @@ NEXT_PAGE(level2_ident_pgt)
NEXT_PAGE(level3_kernel_pgt)
.fill L3_START_KERNEL,8,0
/* (2^48-(2*1024*1024*1024)-((2^39)*511))/(2^30) = 510 */
- .quad level2_kernel_pgt - __START_KERNEL_map + _KERNPG_TABLE
- .quad level2_fixmap_pgt - __START_KERNEL_map + _PAGE_TABLE
+ .quad level2_kernel_pgt - __START_KERNEL_map + _KERNPG_TABLE_NOENC
+ .quad level2_fixmap_pgt - __START_KERNEL_map + _PAGE_TABLE_NOENC

NEXT_PAGE(level2_kernel_pgt)
/*
@@ -514,7 +514,7 @@ NEXT_PAGE(level2_kernel_pgt)

NEXT_PAGE(level2_fixmap_pgt)
.fill 506,8,0
- .quad level1_fixmap_pgt - __START_KERNEL_map + _PAGE_TABLE
+ .quad level1_fixmap_pgt - __START_KERNEL_map + _PAGE_TABLE_NOENC
/* 8MB reserved for vsyscalls + a 2MB hole = 4 + 1 entries */
.fill 5,8,0

diff --git a/arch/x86/mm/kasan_init_64.c b/arch/x86/mm/kasan_init_64.c
index 66d2017..072a70a 100644
--- a/arch/x86/mm/kasan_init_64.c
+++ b/arch/x86/mm/kasan_init_64.c
@@ -70,7 +70,7 @@ static int kasan_die_handler(struct notifier_block *self,
void __init kasan_early_init(void)
{
int i;
- pteval_t pte_val = __pa_nodebug(kasan_zero_page) | __PAGE_KERNEL;
+ pteval_t pte_val = __pa_nodebug(kasan_zero_page) | __PAGE_KERNEL | _PAGE_ENC;
pmdval_t pmd_val = __pa_nodebug(kasan_zero_pte) | _KERNPG_TABLE;
pudval_t pud_val = __pa_nodebug(kasan_zero_pmd) | _KERNPG_TABLE;

@@ -132,7 +132,7 @@ void __init kasan_init(void)
*/
memset(kasan_zero_page, 0, PAGE_SIZE);
for (i = 0; i < PTRS_PER_PTE; i++) {
- pte_t pte = __pte(__pa(kasan_zero_page) | __PAGE_KERNEL_RO);
+ pte_t pte = __pte(__pa(kasan_zero_page) | __PAGE_KERNEL_RO | _PAGE_ENC);
set_pte(&kasan_zero_pte[i], pte);
}
/* Flush TLBs again to be sure that write protection applied. */
diff --git a/arch/x86/mm/mem_encrypt.c b/arch/x86/mm/mem_encrypt.c
index b99d469..d71df97 100644
--- a/arch/x86/mm/mem_encrypt.c
+++ b/arch/x86/mm/mem_encrypt.c
@@ -11,6 +11,10 @@
*/

#include <linux/linkage.h>
+#include <linux/init.h>
+#include <linux/mm.h>
+
+extern pmdval_t early_pmd_flags;

/*
* Since SME related variables are set early in the boot process they must
@@ -19,3 +23,19 @@
*/
unsigned long sme_me_mask __section(.data) = 0;
EXPORT_SYMBOL_GPL(sme_me_mask);
+
+void __init sme_early_init(void)
+{
+ unsigned int i;
+
+ if (!sme_me_mask)
+ return;
+
+ early_pmd_flags |= sme_me_mask;
+
+ __supported_pte_mask |= sme_me_mask;
+
+ /* Update the protection map with memory encryption mask */
+ for (i = 0; i < ARRAY_SIZE(protection_map); i++)
+ protection_map[i] = pgprot_encrypted(protection_map[i]);
+}
diff --git a/arch/x86/mm/pageattr.c b/arch/x86/mm/pageattr.c
index a57e8e0..91c5c63 100644
--- a/arch/x86/mm/pageattr.c
+++ b/arch/x86/mm/pageattr.c
@@ -1987,6 +1987,9 @@ int kernel_map_pages_in_pgd(pgd_t *pgd, u64 pfn, unsigned long address,
if (!(page_flags & _PAGE_RW))
cpa.mask_clr = __pgprot(_PAGE_RW);

+ if (!(page_flags & _PAGE_ENC))
+ cpa.mask_clr = __pgprot(pgprot_val(cpa.mask_clr) | _PAGE_ENC);
+
cpa.mask_set = __pgprot(_PAGE_PRESENT | page_flags);

retval = __change_page_attr_set_clr(&cpa, 0);
diff --git a/include/asm-generic/pgtable.h b/include/asm-generic/pgtable.h
index 18af2bc..4a24451 100644
--- a/include/asm-generic/pgtable.h
+++ b/include/asm-generic/pgtable.h
@@ -314,6 +314,14 @@ static inline int pmd_same(pmd_t pmd_a, pmd_t pmd_b)
#define pgprot_device pgprot_noncached
#endif

+#ifndef pgprot_encrypted
+#define pgprot_encrypted(prot) (prot)
+#endif
+
+#ifndef pgprot_decrypted
+#define pgprot_decrypted(prot) (prot)
+#endif
+
#ifndef pgprot_modify
#define pgprot_modify pgprot_modify
static inline pgprot_t pgprot_modify(pgprot_t oldprot, pgprot_t newprot)