[RFC v2 11/26] mm/asi: Functions to clear ASI page-table entries for a VA range

[Alexandre Chartre <alexandre.chartre@oracle.com>]

Provide functions to clear page-table entries in the ASI page-table for
a specified VA range. Functions also check that the clearing effectively
happens in the ASI page-table and there is no crossing of the ASI
page-table boundary (through references to the kernel page table), so
that the kernel page table is not modified by mistake.

As information (address, size, page-table level) about VA ranges mapped
to the ASI page-table is tracked, clearing is done with just specifying
the start address of the range.

Signed-off-by: Alexandre Chartre <alexandre.chartre@oracle.com>
---
 arch/x86/include/asm/asi.h  |    1 +
 arch/x86/mm/asi_pagetable.c |  134 +++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 135 insertions(+), 0 deletions(-)

diff --git a/arch/x86/include/asm/asi.h b/arch/x86/include/asm/asi.h
index be1c190..919129f 100644
--- a/arch/x86/include/asm/asi.h
+++ b/arch/x86/include/asm/asi.h
@@ -83,6 +83,7 @@ extern bool asi_fault(struct pt_regs *regs, unsigned long error_code,
 extern int asi_map_range(struct asi *asi, void *ptr, size_t size,
 			 enum page_table_level level);
 extern int asi_map(struct asi *asi, void *ptr, unsigned long size);
+extern void asi_unmap(struct asi *asi, void *ptr);
 
 /*
  * Copy the memory mapping for the current module. This is defined as a
diff --git a/arch/x86/mm/asi_pagetable.c b/arch/x86/mm/asi_pagetable.c
index a09a22d..7aee236 100644
--- a/arch/x86/mm/asi_pagetable.c
+++ b/arch/x86/mm/asi_pagetable.c
@@ -670,3 +670,137 @@ int asi_map(struct asi *asi, void *ptr, unsigned long size)
 	return asi_map_range(asi, ptr, size, PGT_LEVEL_PTE);
 }
 EXPORT_SYMBOL(asi_map);
+
+static void asi_clear_pte_range(struct asi *asi, pmd_t *pmd,
+				unsigned long addr, unsigned long end)
+{
+	pte_t *pte;
+
+	pte = asi_pte_offset(asi, pmd, addr);
+	if (IS_ERR(pte))
+		return;
+
+	do {
+		pte_clear(NULL, addr, pte);
+	} while (pte++, addr += PAGE_SIZE, addr < end);
+}
+
+static void asi_clear_pmd_range(struct asi *asi, pud_t *pud,
+				unsigned long addr, unsigned long end,
+				enum page_table_level level)
+{
+	unsigned long next;
+	pmd_t *pmd;
+
+	pmd = asi_pmd_offset(asi, pud, addr);
+	if (IS_ERR(pmd))
+		return;
+
+	do {
+		next = pmd_addr_end(addr, end);
+		if (pmd_none(*pmd) || pmd_present(*pmd))
+			continue;
+		if (level == PGT_LEVEL_PMD || pmd_trans_huge(*pmd) ||
+		    pmd_devmap(*pmd)) {
+			pmd_clear(pmd);
+			continue;
+		}
+		asi_clear_pte_range(asi, pmd, addr, next);
+	} while (pmd++, addr = next, addr < end);
+}
+
+static void asi_clear_pud_range(struct asi *asi, p4d_t *p4d,
+				unsigned long addr, unsigned long end,
+				enum page_table_level level)
+{
+	unsigned long next;
+	pud_t *pud;
+
+	pud = asi_pud_offset(asi, p4d, addr);
+	if (IS_ERR(pud))
+		return;
+
+	do {
+		next = pud_addr_end(addr, end);
+		if (pud_none(*pud))
+			continue;
+		if (level == PGT_LEVEL_PUD || pud_trans_huge(*pud) ||
+		    pud_devmap(*pud)) {
+			pud_clear(pud);
+			continue;
+		}
+		asi_clear_pmd_range(asi, pud, addr, next, level);
+	} while (pud++, addr = next, addr < end);
+}
+
+static void asi_clear_p4d_range(struct asi *asi, pgd_t *pgd,
+				unsigned long addr, unsigned long end,
+				enum page_table_level level)
+{
+	unsigned long next;
+	p4d_t *p4d;
+
+	p4d = asi_p4d_offset(asi, pgd, addr);
+	if (IS_ERR(p4d))
+		return;
+
+	do {
+		next = p4d_addr_end(addr, end);
+		if (p4d_none(*p4d))
+			continue;
+		if (level == PGT_LEVEL_P4D) {
+			p4d_clear(p4d);
+			continue;
+		}
+		asi_clear_pud_range(asi, p4d, addr, next, level);
+	} while (p4d++, addr = next, addr < end);
+}
+
+static void asi_clear_pgd_range(struct asi *asi, pgd_t *pagetable,
+				unsigned long addr, unsigned long end,
+				enum page_table_level level)
+{
+	unsigned long next;
+	pgd_t *pgd;
+
+	pgd = pgd_offset_pgd(pagetable, addr);
+	do {
+		next = pgd_addr_end(addr, end);
+		if (pgd_none(*pgd))
+			continue;
+		if (level == PGT_LEVEL_PGD) {
+			pgd_clear(pgd);
+			continue;
+		}
+		asi_clear_p4d_range(asi, pgd, addr, next, level);
+	} while (pgd++, addr = next, addr < end);
+}
+
+/*
+ * Clear page table entries in the specified ASI page-table.
+ */
+void asi_unmap(struct asi *asi, void *ptr)
+{
+	struct asi_range_mapping *range_mapping;
+	unsigned long addr, end;
+	unsigned long flags;
+
+	spin_lock_irqsave(&asi->lock, flags);
+
+	range_mapping = asi_get_range_mapping(asi, ptr);
+	if (!range_mapping) {
+		pr_debug("ASI %p: UNMAP %px - not mapped\n", asi, ptr);
+		goto done;
+	}
+
+	addr = (unsigned long)range_mapping->ptr;
+	end = addr + range_mapping->size;
+	pr_debug("ASI %p: UNMAP %px/%lx/%d\n", asi, ptr,
+		 range_mapping->size, range_mapping->level);
+	asi_clear_pgd_range(asi, asi->pgd, addr, end, range_mapping->level);
+	list_del(&range_mapping->list);
+	kfree(range_mapping);
+done:
+	spin_unlock_irqrestore(&asi->lock, flags);
+}
+EXPORT_SYMBOL(asi_unmap);
-- 
1.7.1