[PATCH RFC 29/37] mm: arm64: Define the PAGE_METADATA_NONE page protection

[Alexandru Elisei]

Define the PAGE_METADATA_NONE page protection to be used when a page with
metadata doesn't have metadata storage reserved.

For arm64, this is accomplished by adding a new page table entry software
bit PTE_METADATA_NONE. Linux doesn't set any of the PBHA bits in entries
from the last level of the translation table and it doesn't use the
TCR_ELx.HWUxx bits.  This makes it safe to define PTE_METADATA_NONE as bit
59.

Signed-off-by: Alexandru Elisei <alexandru.elisei@xxxxxxx>
---
 arch/arm64/include/asm/pgtable-prot.h |  2 ++
 arch/arm64/include/asm/pgtable.h      | 16 ++++++++++++++--
 include/linux/pgtable.h               | 12 ++++++++++++
 3 files changed, 28 insertions(+), 2 deletions(-)

diff --git a/arch/arm64/include/asm/pgtable-prot.h b/arch/arm64/include/asm/pgtable-prot.h
index eed814b00a38..ed2a98ec4e95 100644
--- a/arch/arm64/include/asm/pgtable-prot.h
+++ b/arch/arm64/include/asm/pgtable-prot.h
@@ -19,6 +19,7 @@
 #define PTE_SPECIAL		(_AT(pteval_t, 1) << 56)
 #define PTE_DEVMAP		(_AT(pteval_t, 1) << 57)
 #define PTE_PROT_NONE		(_AT(pteval_t, 1) << 58) /* only when !PTE_VALID */
+#define PTE_METADATA_NONE	(_AT(pteval_t, 1) << 59) /* only when PTE_PROT_NONE */
 
 /*
  * This bit indicates that the entry is present i.e. pmd_page()
@@ -98,6 +99,7 @@ extern bool arm64_use_ng_mappings;
 	 })
 
 #define PAGE_NONE		__pgprot(((_PAGE_DEFAULT) & ~PTE_VALID) | PTE_PROT_NONE | PTE_RDONLY | PTE_NG | PTE_PXN | PTE_UXN)
+#define PAGE_METADATA_NONE	__pgprot((_PAGE_DEFAULT & ~PTE_VALID) | PTE_PROT_NONE | PTE_METADATA_NONE | PTE_RDONLY | PTE_NG | PTE_PXN | PTE_UXN)
 /* shared+writable pages are clean by default, hence PTE_RDONLY|PTE_WRITE */
 #define PAGE_SHARED		__pgprot(_PAGE_SHARED)
 #define PAGE_SHARED_EXEC	__pgprot(_PAGE_SHARED_EXEC)
diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h
index 944860d7090e..2e42f7713425 100644
--- a/arch/arm64/include/asm/pgtable.h
+++ b/arch/arm64/include/asm/pgtable.h
@@ -451,6 +451,18 @@ static inline int pmd_protnone(pmd_t pmd)
 }
 #endif
 
+#ifdef CONFIG_MEMORY_METADATA
+static inline bool pte_metadata_none(pte_t pte)
+{
+	return (((pte_val(pte) & (PTE_VALID | PTE_PROT_NONE)) == PTE_PROT_NONE)
+		&& (pte_val(pte) & PTE_METADATA_NONE));
+}
+static inline bool pmd_metadata_none(pmd_t pmd)
+{
+	return pte_metadata_none(pmd_pte(pmd));
+}
+#endif
+
 #define pmd_present_invalid(pmd)     (!!(pmd_val(pmd) & PMD_PRESENT_INVALID))
 
 static inline int pmd_present(pmd_t pmd)
@@ -809,8 +821,8 @@ static inline pte_t pte_modify(pte_t pte, pgprot_t newprot)
 	 * in MAIR_EL1. The mask below has to include PTE_ATTRINDX_MASK.
 	 */
 	const pteval_t mask = PTE_USER | PTE_PXN | PTE_UXN | PTE_RDONLY |
-			      PTE_PROT_NONE | PTE_VALID | PTE_WRITE | PTE_GP |
-			      PTE_ATTRINDX_MASK;
+			      PTE_PROT_NONE | PTE_METADATA_NONE | PTE_VALID |
+			      PTE_WRITE | PTE_GP | PTE_ATTRINDX_MASK;
 	/* preserve the hardware dirty information */
 	if (pte_hw_dirty(pte))
 		pte = pte_mkdirty(pte);
diff --git a/include/linux/pgtable.h b/include/linux/pgtable.h
index 5063b482e34f..0119ffa2c0ab 100644
--- a/include/linux/pgtable.h
+++ b/include/linux/pgtable.h
@@ -1340,6 +1340,18 @@ static inline int pmd_protnone(pmd_t pmd)
 }
 #endif /* CONFIG_NUMA_BALANCING */
 
+#ifndef CONFIG_MEMORY_METADATA
+static inline bool pte_metadata_none(pte_t pte)
+{
+	return false;
+}
+
+static inline bool pmd_metadata_none(pmd_t pmd)
+{
+	return false;
+}
+#endif /* CONFIG_MEMORY_METADATA */
+
 #endif /* CONFIG_MMU */
 
 #ifdef CONFIG_HAVE_ARCH_HUGE_VMAP
-- 
2.41.0