drivers/char/mspec.c

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