From: Almudena Garcia <liberamenso10000@gmail.com>
Date: Mon, 10 Aug 2020 19:56:22 +0200
Subject: [PATCH 3/6] vm_kern: Add kmem_alloc_aligned_table

This function allows to map a table in a memory page,
using its physical address,aligning the start of the page with the start of the table

*vm/vm_kern.c (kmem_alloc_aligned_table): New function. Returns a reference for the virtual address of the table.
*vm/vm_kern.h (kmem_alloc_aligned_table): New prototype
---
diff --git a/vm/vm_kern.c b/vm/vm_kern.c
index 2e333ee1..d7530825 100644
--- a/vm/vm_kern.c
+++ b/vm/vm_kern.c
@@ -635,6 +635,45 @@ retry:
 	return KERN_SUCCESS;
 }
+/*
+ * kmem_map_aligned_table: map a table or structure in a virtual memory page
+ * Align the table initial address with the page initial address.
+ *
+ * Parameters:
+ * phys_address: physical address, the start address of the table.
+ * size: size of the table.
+ * mode: access mode. VM_PROT_READ for read, VM_PROT_WRITE for write.
+ *
+ * Returns a reference to the virtual address if success, NULL if failure.
+ */
+
+void*
+kmem_map_aligned_table(
+	phys_addr_t		phys_address,
+	vm_size_t	size,
+	int		mode)
+{
+	vm_offset_t virt_addr;
+	kern_return_t ret;
+	uintptr_t into_page = phys_address % PAGE_SIZE;
+	uintptr_t nearest_page = (uintptr_t)trunc_page(phys_address);
+
+	size += into_page;
+
+	ret = kmem_alloc_wired(kernel_map, &virt_addr,
+				round_page(size));
+
+	if (ret != KERN_SUCCESS)
+		return NULL;
+
+	(void) pmap_map_bd(virt_addr, nearest_page,
+				nearest_page + round_page(size), mode);
+
+	/* XXX remember mapping somewhere so we can free it? */
+
+	return (void *) (virt_addr + into_page);
+}
+
diff --git a/vm/vm_kern.h b/vm/vm_kern.h
index 0cdb19db..9d43d9e2 100644
--- a/vm/vm_kern.h
+++ b/vm/vm_kern.h
@@ -55,6 +55,8 @@ extern kern_return_t	kmem_alloc_pageable(vm_map_t, vm_offset_t *,
 extern kern_return_t	kmem_valloc(vm_map_t, vm_offset_t *, vm_size_t);
 extern kern_return_t	kmem_alloc_wired(vm_map_t, vm_offset_t *, vm_size_t);
 extern kern_return_t	kmem_alloc_aligned(vm_map_t, vm_offset_t *, vm_size_t);
+extern void*		kmem_map_aligned_table(phys_addr_t, vm_size_t, int);
+
 extern void		kmem_free(vm_map_t, vm_offset_t, vm_size_t);
 
 extern void		kmem_submap(vm_map_t, vm_map_t, vm_offset_t *,