[PATCH 11/26] mm: asi: ASI page table allocation functions

[Brendan Jackman <jackmanb@google.com>]

From: Junaid Shahid <junaids@google.com>

This adds custom allocation and free functions for ASI page tables.

The alloc functions support allocating memory using different GFP
reclaim flags, in order to be able to support non-sensitive allocations
from both standard and atomic contexts. They also install the page
tables locklessly, which makes it slightly simpler to handle
non-sensitive allocations from interrupts/exceptions.

Signed-off-by: Junaid Shahid <junaids@google.com>
Signed-off-by: Brendan Jackman <jackmanb@google.com>
---
 arch/x86/mm/asi.c | 59 +++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 59 insertions(+)

diff --git a/arch/x86/mm/asi.c b/arch/x86/mm/asi.c
index 0ba156f879d3..8798aab66748 100644
--- a/arch/x86/mm/asi.c
+++ b/arch/x86/mm/asi.c
@@ -71,6 +71,65 @@ void asi_unregister_class(int index)
 }
 EXPORT_SYMBOL_GPL(asi_unregister_class);
 
+#ifndef mm_inc_nr_p4ds
+#define mm_inc_nr_p4ds(mm)	do {} while (false)
+#endif
+
+#ifndef mm_dec_nr_p4ds
+#define mm_dec_nr_p4ds(mm)	do {} while (false)
+#endif
+
+#define pte_offset		pte_offset_kernel
+
+/*
+ * asi_p4d_alloc, asi_pud_alloc, asi_pmd_alloc, asi_pte_alloc.
+ *
+ * These are like the normal xxx_alloc functions, but:
+ *
+ *  - They use atomic operations instead of taking a spinlock; this allows them
+ *    to be used from interrupts. This is necessary because we use the page
+ *    allocator from interrupts and the page allocator ultimately calls this
+ *    code.
+ *  - They support customizing the allocation flags.
+ *
+ * On the other hand, they do not use the normal page allocation infrastructure,
+ * that means that PTE pages do not have the PageTable type nor the PagePgtable
+ * flag and we don't increment the meminfo stat (NR_PAGETABLE) as they do.
+ */
+static_assert(!IS_ENABLED(CONFIG_PARAVIRT));
+#define DEFINE_ASI_PGTBL_ALLOC(base, level)				\
+__maybe_unused								\
+static level##_t * asi_##level##_alloc(struct asi *asi,			\
+				       base##_t *base, ulong addr,	\
+				       gfp_t flags)			\
+{									\
+	if (unlikely(base##_none(*base))) {				\
+		ulong pgtbl = get_zeroed_page(flags);			\
+		phys_addr_t pgtbl_pa;					\
+									\
+		if (!pgtbl)						\
+			return NULL;					\
+									\
+		pgtbl_pa = __pa(pgtbl);					\
+									\
+		if (cmpxchg((ulong *)base, 0,				\
+			    pgtbl_pa | _PAGE_TABLE) != 0) {		\
+			free_page(pgtbl);				\
+			goto out;					\
+		}							\
+									\
+		mm_inc_nr_##level##s(asi->mm);				\
+	}								\
+out:									\
+	VM_BUG_ON(base##_leaf(*base));					\
+	return level##_offset(base, addr);				\
+}
+
+DEFINE_ASI_PGTBL_ALLOC(pgd, p4d)
+DEFINE_ASI_PGTBL_ALLOC(p4d, pud)
+DEFINE_ASI_PGTBL_ALLOC(pud, pmd)
+DEFINE_ASI_PGTBL_ALLOC(pmd, pte)
+
 void __init asi_check_boottime_disable(void)
 {
 	bool enabled = IS_ENABLED(CONFIG_MITIGATION_ADDRESS_SPACE_ISOLATION_DEFAULT_ON);

-- 
2.45.2.993.g49e7a77208-goog