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 <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
  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
 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
 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
 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         vma->vm_flags |= 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
 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
 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
 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
 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");