[RFC 6/8] arm64/mm: introduce pgtable allocator for head

[Pingfan Liu]

>From the view of __create_pgd_mapping(), both idmap_pg_dir and
init_pg_dir can be treated as a memory pool.  Introduce an allocator
working on them, so __create_pgd_mapping() can create mapping.

Signed-off-by: Pingfan Liu <kernelfans at gmail.com>
Cc: Catalin Marinas <catalin.marinas at arm.com>
Cc: Will Deacon <will at kernel.org>
Cc: Marc Zyngier <maz at kernel.org>
Cc: Kristina Martsenko <kristina.martsenko at arm.com>
Cc: James Morse <james.morse at arm.com>
Cc: Steven Price <steven.price at arm.com>
Cc: Jonathan Cameron <Jonathan.Cameron at huawei.com>
Cc: Pavel Tatashin <pasha.tatashin at soleen.com>
Cc: Anshuman Khandual <anshuman.khandual at arm.com>
Cc: Atish Patra <atish.patra at wdc.com>
Cc: Mike Rapoport <rppt at kernel.org>
Cc: Logan Gunthorpe <logang at deltatee.com>
Cc: Mark Brown <broonie at kernel.org>
To: linux-arm-kernel at lists.infradead.org
---
 arch/arm64/mm/mmu.c | 22 ++++++++++++++++++++++
 1 file changed, 22 insertions(+)

diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c
index 628752c3cfd0..b546e47543e2 100644
--- a/arch/arm64/mm/mmu.c
+++ b/arch/arm64/mm/mmu.c
@@ -86,6 +86,28 @@ pgprot_t phys_mem_access_prot(struct file *file, unsigned long pfn,
 }
 EXPORT_SYMBOL(phys_mem_access_prot);
 
+struct mempool {
+	unsigned long start;
+	unsigned long size;
+	unsigned long next_idx;
+};
+
+struct mempool cur_pool;
+
+void set_cur_mempool(unsigned long start, unsigned long size)
+{
+	cur_pool.start = start;
+	cur_pool.size = size;
+	cur_pool.next_idx = 0;
+}
+
+unsigned long __init head_pgtable_alloc(unsigned long unused_a, void *unused_b)
+{
+	unsigned long idx = cur_pool.next_idx++;
+
+	return cur_pool.start + (idx << PAGE_SHIFT);
+}
+
 static unsigned long __init early_pgtable_alloc(unsigned long unused_a, void *unused_b)
 {
 	phys_addr_t phys;
-- 
2.29.2