linux/drivers/char/mspec.c
Gustavo A. R. Silva 3c2faf61fb char: mspec: Replace zero-length array with flexible-array member
The current codebase makes use of the zero-length array language
extension to the C90 standard, but the preferred mechanism to declare
variable-length types such as these ones is a flexible array member[1][2],
introduced in C99:

struct foo {
        int stuff;
        struct boo array[];
};

By making use of the mechanism above, we will get a compiler warning
in case the flexible array does not occur last in the structure, which
will help us prevent some kind of undefined behavior bugs from being
inadvertently introduced[3] to the codebase from now on.

Also, notice that, dynamic memory allocations won't be affected by
this change:

"Flexible array members have incomplete type, and so the sizeof operator
may not be applied. As a quirk of the original implementation of
zero-length arrays, sizeof evaluates to zero."[1]

This issue was found with the help of Coccinelle.

[1] https://gcc.gnu.org/onlinedocs/gcc/Zero-Length.html
[2] https://github.com/KSPP/linux/issues/21
[3] commit 7649773293 ("cxgb3/l2t: Fix undefined behaviour")

Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>
Link: https://lore.kernel.org/r/20200227184808.GA1925@embeddedor
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
2020-03-19 07:41:03 +01:00

300 lines
7.2 KiB
C

// SPDX-License-Identifier: GPL-2.0-only
/*
* Copyright (C) 2001-2006 Silicon Graphics, Inc. All rights
* reserved.
*/
/*
* SN Platform Special Memory (mspec) Support
*
* This driver exports the SN special memory (mspec) facility to user
* processes.
* There are two types of memory made available thru this driver:
* uncached and cached.
*
* Uncached are used for memory write combining feature of the ia64
* cpu.
*
* Cached are used for areas of memory that are used as cached addresses
* on our partition and used as uncached addresses from other partitions.
* Due to a design constraint of the SN2 Shub, you can not have processors
* on the same FSB perform both a cached and uncached reference to the
* same cache line. These special memory cached regions prevent the
* kernel from ever dropping in a TLB entry and therefore prevent the
* processor from ever speculating a cache line from this page.
*/
#include <linux/types.h>
#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/init.h>
#include <linux/errno.h>
#include <linux/miscdevice.h>
#include <linux/spinlock.h>
#include <linux/mm.h>
#include <linux/fs.h>
#include <linux/vmalloc.h>
#include <linux/string.h>
#include <linux/slab.h>
#include <linux/numa.h>
#include <linux/refcount.h>
#include <asm/page.h>
#include <asm/pgtable.h>
#include <linux/atomic.h>
#include <asm/tlbflush.h>
#include <asm/uncached.h>
#define CACHED_ID "Cached,"
#define UNCACHED_ID "Uncached"
#define REVISION "4.0"
#define MSPEC_BASENAME "mspec"
/*
* Page types allocated by the device.
*/
enum mspec_page_type {
MSPEC_CACHED = 2,
MSPEC_UNCACHED
};
/*
* One of these structures is allocated when an mspec region is mmaped. The
* structure is pointed to by the vma->vm_private_data field in the vma struct.
* This structure is used to record the addresses of the mspec pages.
* This structure is shared by all vma's that are split off from the
* original vma when split_vma()'s are done.
*
* The refcnt is incremented atomically because mm->mmap_sem does not
* protect in fork case where multiple tasks share the vma_data.
*/
struct vma_data {
refcount_t refcnt; /* Number of vmas sharing the data. */
spinlock_t lock; /* Serialize access to this structure. */
int count; /* Number of pages allocated. */
enum mspec_page_type type; /* Type of pages allocated. */
unsigned long vm_start; /* Original (unsplit) base. */
unsigned long vm_end; /* Original (unsplit) end. */
unsigned long maddr[]; /* Array of MSPEC addresses. */
};
/*
* mspec_open
*
* Called when a device mapping is created by a means other than mmap
* (via fork, munmap, etc.). Increments the reference count on the
* underlying mspec data so it is not freed prematurely.
*/
static void
mspec_open(struct vm_area_struct *vma)
{
struct vma_data *vdata;
vdata = vma->vm_private_data;
refcount_inc(&vdata->refcnt);
}
/*
* mspec_close
*
* Called when unmapping a device mapping. Frees all mspec pages
* belonging to all the vma's sharing this vma_data structure.
*/
static void
mspec_close(struct vm_area_struct *vma)
{
struct vma_data *vdata;
int index, last_index;
unsigned long my_page;
vdata = vma->vm_private_data;
if (!refcount_dec_and_test(&vdata->refcnt))
return;
last_index = (vdata->vm_end - vdata->vm_start) >> PAGE_SHIFT;
for (index = 0; index < last_index; index++) {
if (vdata->maddr[index] == 0)
continue;
/*
* Clear the page before sticking it back
* into the pool.
*/
my_page = vdata->maddr[index];
vdata->maddr[index] = 0;
memset((char *)my_page, 0, PAGE_SIZE);
uncached_free_page(my_page, 1);
}
kvfree(vdata);
}
/*
* mspec_fault
*
* Creates a mspec page and maps it to user space.
*/
static vm_fault_t
mspec_fault(struct vm_fault *vmf)
{
unsigned long paddr, maddr;
unsigned long pfn;
pgoff_t index = vmf->pgoff;
struct vma_data *vdata = vmf->vma->vm_private_data;
maddr = (volatile unsigned long) vdata->maddr[index];
if (maddr == 0) {
maddr = uncached_alloc_page(numa_node_id(), 1);
if (maddr == 0)
return VM_FAULT_OOM;
spin_lock(&vdata->lock);
if (vdata->maddr[index] == 0) {
vdata->count++;
vdata->maddr[index] = maddr;
} else {
uncached_free_page(maddr, 1);
maddr = vdata->maddr[index];
}
spin_unlock(&vdata->lock);
}
paddr = maddr & ~__IA64_UNCACHED_OFFSET;
pfn = paddr >> PAGE_SHIFT;
return vmf_insert_pfn(vmf->vma, vmf->address, pfn);
}
static const struct vm_operations_struct mspec_vm_ops = {
.open = mspec_open,
.close = mspec_close,
.fault = mspec_fault,
};
/*
* mspec_mmap
*
* Called when mmapping the device. Initializes the vma with a fault handler
* and private data structure necessary to allocate, track, and free the
* underlying pages.
*/
static int
mspec_mmap(struct file *file, struct vm_area_struct *vma,
enum mspec_page_type type)
{
struct vma_data *vdata;
int pages, vdata_size;
if (vma->vm_pgoff != 0)
return -EINVAL;
if ((vma->vm_flags & VM_SHARED) == 0)
return -EINVAL;
if ((vma->vm_flags & VM_WRITE) == 0)
return -EPERM;
pages = vma_pages(vma);
vdata_size = sizeof(struct vma_data) + pages * sizeof(long);
if (vdata_size <= PAGE_SIZE)
vdata = kzalloc(vdata_size, GFP_KERNEL);
else
vdata = vzalloc(vdata_size);
if (!vdata)
return -ENOMEM;
vdata->vm_start = vma->vm_start;
vdata->vm_end = vma->vm_end;
vdata->type = type;
spin_lock_init(&vdata->lock);
refcount_set(&vdata->refcnt, 1);
vma->vm_private_data = vdata;
vma->vm_flags |= VM_IO | VM_PFNMAP | VM_DONTEXPAND | VM_DONTDUMP;
if (vdata->type == MSPEC_UNCACHED)
vma->vm_page_prot = pgprot_noncached(vma->vm_page_prot);
vma->vm_ops = &mspec_vm_ops;
return 0;
}
static int
cached_mmap(struct file *file, struct vm_area_struct *vma)
{
return mspec_mmap(file, vma, MSPEC_CACHED);
}
static int
uncached_mmap(struct file *file, struct vm_area_struct *vma)
{
return mspec_mmap(file, vma, MSPEC_UNCACHED);
}
static const struct file_operations cached_fops = {
.owner = THIS_MODULE,
.mmap = cached_mmap,
.llseek = noop_llseek,
};
static struct miscdevice cached_miscdev = {
.minor = MISC_DYNAMIC_MINOR,
.name = "mspec_cached",
.fops = &cached_fops
};
static const struct file_operations uncached_fops = {
.owner = THIS_MODULE,
.mmap = uncached_mmap,
.llseek = noop_llseek,
};
static struct miscdevice uncached_miscdev = {
.minor = MISC_DYNAMIC_MINOR,
.name = "mspec_uncached",
.fops = &uncached_fops
};
/*
* mspec_init
*
* Called at boot time to initialize the mspec facility.
*/
static int __init
mspec_init(void)
{
int ret;
ret = misc_register(&cached_miscdev);
if (ret) {
printk(KERN_ERR "%s: failed to register device %i\n",
CACHED_ID, ret);
return ret;
}
ret = misc_register(&uncached_miscdev);
if (ret) {
printk(KERN_ERR "%s: failed to register device %i\n",
UNCACHED_ID, ret);
misc_deregister(&cached_miscdev);
return ret;
}
printk(KERN_INFO "%s %s initialized devices: %s %s\n",
MSPEC_BASENAME, REVISION, CACHED_ID, UNCACHED_ID);
return 0;
}
static void __exit
mspec_exit(void)
{
misc_deregister(&uncached_miscdev);
misc_deregister(&cached_miscdev);
}
module_init(mspec_init);
module_exit(mspec_exit);
MODULE_AUTHOR("Silicon Graphics, Inc. <linux-altix@sgi.com>");
MODULE_DESCRIPTION("Driver for SGI SN special memory operations");
MODULE_LICENSE("GPL");