xref: /openbmc/linux/drivers/char/mspec.c (revision 1c71222e)
1 // SPDX-License-Identifier: GPL-2.0-only
2 /*
3  * Copyright (C) 2001-2006 Silicon Graphics, Inc.  All rights
4  * reserved.
5  */
6 
7 /*
8  * SN Platform Special Memory (mspec) Support
9  *
10  * This driver exports the SN special memory (mspec) facility to user
11  * processes.
12  * There are two types of memory made available thru this driver:
13  * uncached and cached.
14  *
15  * Uncached are used for memory write combining feature of the ia64
16  * cpu.
17  *
18  * Cached are used for areas of memory that are used as cached addresses
19  * on our partition and used as uncached addresses from other partitions.
20  * Due to a design constraint of the SN2 Shub, you can not have processors
21  * on the same FSB perform both a cached and uncached reference to the
22  * same cache line.  These special memory cached regions prevent the
23  * kernel from ever dropping in a TLB entry and therefore prevent the
24  * processor from ever speculating a cache line from this page.
25  */
26 
27 #include <linux/types.h>
28 #include <linux/kernel.h>
29 #include <linux/module.h>
30 #include <linux/init.h>
31 #include <linux/errno.h>
32 #include <linux/miscdevice.h>
33 #include <linux/spinlock.h>
34 #include <linux/mm.h>
35 #include <linux/fs.h>
36 #include <linux/vmalloc.h>
37 #include <linux/string.h>
38 #include <linux/slab.h>
39 #include <linux/numa.h>
40 #include <linux/refcount.h>
41 #include <asm/page.h>
42 #include <linux/atomic.h>
43 #include <asm/tlbflush.h>
44 #include <asm/uncached.h>
45 
46 
47 #define CACHED_ID	"Cached,"
48 #define UNCACHED_ID	"Uncached"
49 #define REVISION	"4.0"
50 #define MSPEC_BASENAME	"mspec"
51 
52 /*
53  * Page types allocated by the device.
54  */
55 enum mspec_page_type {
56 	MSPEC_CACHED = 2,
57 	MSPEC_UNCACHED
58 };
59 
60 /*
61  * One of these structures is allocated when an mspec region is mmaped. The
62  * structure is pointed to by the vma->vm_private_data field in the vma struct.
63  * This structure is used to record the addresses of the mspec pages.
64  * This structure is shared by all vma's that are split off from the
65  * original vma when split_vma()'s are done.
66  *
67  * The refcnt is incremented atomically because mm->mmap_lock does not
68  * protect in fork case where multiple tasks share the vma_data.
69  */
70 struct vma_data {
71 	refcount_t refcnt;	/* Number of vmas sharing the data. */
72 	spinlock_t lock;	/* Serialize access to this structure. */
73 	int count;		/* Number of pages allocated. */
74 	enum mspec_page_type type; /* Type of pages allocated. */
75 	unsigned long vm_start;	/* Original (unsplit) base. */
76 	unsigned long vm_end;	/* Original (unsplit) end. */
77 	unsigned long maddr[];	/* Array of MSPEC addresses. */
78 };
79 
80 /*
81  * mspec_open
82  *
83  * Called when a device mapping is created by a means other than mmap
84  * (via fork, munmap, etc.).  Increments the reference count on the
85  * underlying mspec data so it is not freed prematurely.
86  */
87 static void
mspec_open(struct vm_area_struct * vma)88 mspec_open(struct vm_area_struct *vma)
89 {
90 	struct vma_data *vdata;
91 
92 	vdata = vma->vm_private_data;
93 	refcount_inc(&vdata->refcnt);
94 }
95 
96 /*
97  * mspec_close
98  *
99  * Called when unmapping a device mapping. Frees all mspec pages
100  * belonging to all the vma's sharing this vma_data structure.
101  */
102 static void
mspec_close(struct vm_area_struct * vma)103 mspec_close(struct vm_area_struct *vma)
104 {
105 	struct vma_data *vdata;
106 	int index, last_index;
107 	unsigned long my_page;
108 
109 	vdata = vma->vm_private_data;
110 
111 	if (!refcount_dec_and_test(&vdata->refcnt))
112 		return;
113 
114 	last_index = (vdata->vm_end - vdata->vm_start) >> PAGE_SHIFT;
115 	for (index = 0; index < last_index; index++) {
116 		if (vdata->maddr[index] == 0)
117 			continue;
118 		/*
119 		 * Clear the page before sticking it back
120 		 * into the pool.
121 		 */
122 		my_page = vdata->maddr[index];
123 		vdata->maddr[index] = 0;
124 		memset((char *)my_page, 0, PAGE_SIZE);
125 		uncached_free_page(my_page, 1);
126 	}
127 
128 	kvfree(vdata);
129 }
130 
131 /*
132  * mspec_fault
133  *
134  * Creates a mspec page and maps it to user space.
135  */
136 static vm_fault_t
mspec_fault(struct vm_fault * vmf)137 mspec_fault(struct vm_fault *vmf)
138 {
139 	unsigned long paddr, maddr;
140 	unsigned long pfn;
141 	pgoff_t index = vmf->pgoff;
142 	struct vma_data *vdata = vmf->vma->vm_private_data;
143 
144 	maddr = (volatile unsigned long) vdata->maddr[index];
145 	if (maddr == 0) {
146 		maddr = uncached_alloc_page(numa_node_id(), 1);
147 		if (maddr == 0)
148 			return VM_FAULT_OOM;
149 
150 		spin_lock(&vdata->lock);
151 		if (vdata->maddr[index] == 0) {
152 			vdata->count++;
153 			vdata->maddr[index] = maddr;
154 		} else {
155 			uncached_free_page(maddr, 1);
156 			maddr = vdata->maddr[index];
157 		}
158 		spin_unlock(&vdata->lock);
159 	}
160 
161 	paddr = maddr & ~__IA64_UNCACHED_OFFSET;
162 	pfn = paddr >> PAGE_SHIFT;
163 
164 	return vmf_insert_pfn(vmf->vma, vmf->address, pfn);
165 }
166 
167 static const struct vm_operations_struct mspec_vm_ops = {
168 	.open = mspec_open,
169 	.close = mspec_close,
170 	.fault = mspec_fault,
171 };
172 
173 /*
174  * mspec_mmap
175  *
176  * Called when mmapping the device.  Initializes the vma with a fault handler
177  * and private data structure necessary to allocate, track, and free the
178  * underlying pages.
179  */
180 static int
mspec_mmap(struct file * file,struct vm_area_struct * vma,enum mspec_page_type type)181 mspec_mmap(struct file *file, struct vm_area_struct *vma,
182 					enum mspec_page_type type)
183 {
184 	struct vma_data *vdata;
185 	int pages, vdata_size;
186 
187 	if (vma->vm_pgoff != 0)
188 		return -EINVAL;
189 
190 	if ((vma->vm_flags & VM_SHARED) == 0)
191 		return -EINVAL;
192 
193 	if ((vma->vm_flags & VM_WRITE) == 0)
194 		return -EPERM;
195 
196 	pages = vma_pages(vma);
197 	vdata_size = sizeof(struct vma_data) + pages * sizeof(long);
198 	vdata = kvzalloc(vdata_size, GFP_KERNEL);
199 	if (!vdata)
200 		return -ENOMEM;
201 
202 	vdata->vm_start = vma->vm_start;
203 	vdata->vm_end = vma->vm_end;
204 	vdata->type = type;
205 	spin_lock_init(&vdata->lock);
206 	refcount_set(&vdata->refcnt, 1);
207 	vma->vm_private_data = vdata;
208 
209 	vm_flags_set(vma, VM_IO | VM_PFNMAP | VM_DONTEXPAND | VM_DONTDUMP);
210 	if (vdata->type == MSPEC_UNCACHED)
211 		vma->vm_page_prot = pgprot_noncached(vma->vm_page_prot);
212 	vma->vm_ops = &mspec_vm_ops;
213 
214 	return 0;
215 }
216 
217 static int
cached_mmap(struct file * file,struct vm_area_struct * vma)218 cached_mmap(struct file *file, struct vm_area_struct *vma)
219 {
220 	return mspec_mmap(file, vma, MSPEC_CACHED);
221 }
222 
223 static int
uncached_mmap(struct file * file,struct vm_area_struct * vma)224 uncached_mmap(struct file *file, struct vm_area_struct *vma)
225 {
226 	return mspec_mmap(file, vma, MSPEC_UNCACHED);
227 }
228 
229 static const struct file_operations cached_fops = {
230 	.owner = THIS_MODULE,
231 	.mmap = cached_mmap,
232 	.llseek = noop_llseek,
233 };
234 
235 static struct miscdevice cached_miscdev = {
236 	.minor = MISC_DYNAMIC_MINOR,
237 	.name = "mspec_cached",
238 	.fops = &cached_fops
239 };
240 
241 static const struct file_operations uncached_fops = {
242 	.owner = THIS_MODULE,
243 	.mmap = uncached_mmap,
244 	.llseek = noop_llseek,
245 };
246 
247 static struct miscdevice uncached_miscdev = {
248 	.minor = MISC_DYNAMIC_MINOR,
249 	.name = "mspec_uncached",
250 	.fops = &uncached_fops
251 };
252 
253 /*
254  * mspec_init
255  *
256  * Called at boot time to initialize the mspec facility.
257  */
258 static int __init
mspec_init(void)259 mspec_init(void)
260 {
261 	int ret;
262 
263 	ret = misc_register(&cached_miscdev);
264 	if (ret) {
265 		printk(KERN_ERR "%s: failed to register device %i\n",
266 		       CACHED_ID, ret);
267 		return ret;
268 	}
269 	ret = misc_register(&uncached_miscdev);
270 	if (ret) {
271 		printk(KERN_ERR "%s: failed to register device %i\n",
272 		       UNCACHED_ID, ret);
273 		misc_deregister(&cached_miscdev);
274 		return ret;
275 	}
276 
277 	printk(KERN_INFO "%s %s initialized devices: %s %s\n",
278 	       MSPEC_BASENAME, REVISION, CACHED_ID, UNCACHED_ID);
279 
280 	return 0;
281 }
282 
283 static void __exit
mspec_exit(void)284 mspec_exit(void)
285 {
286 	misc_deregister(&uncached_miscdev);
287 	misc_deregister(&cached_miscdev);
288 }
289 
290 module_init(mspec_init);
291 module_exit(mspec_exit);
292 
293 MODULE_AUTHOR("Silicon Graphics, Inc. <linux-altix@sgi.com>");
294 MODULE_DESCRIPTION("Driver for SGI SN special memory operations");
295 MODULE_LICENSE("GPL");
296