To: Andrew Morton <akpm@osdl.org>
Cc: Linus Torvalds <torvalds@osdl.org>, linux-kernel@vger.kernel.org,
       linux-ia64@vger.kernel.org, Christoph Hellwig <hch@lst.de>,
       Carsten Otte <cotte@de.ibm.com>
Subject: [patch] mspec - special memory driver and do_no_pfn handler
From: Jes Sorensen <jes@sgi.com>
Date: 16 Mar 2006 11:55:48 -0500
Message-ID: <yq0k6auuy5n.fsf@jaguar.mkp.net>
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Hi,

This is an updated version of the mspec driver (special memory
support), formerly known as fetchop.

With this version I have implemented a do_no_pfn() handler, similar to
the do_no_page() handler but for pages which are not backed by a
struct page. This avoids the trick used in earlier versions where the
driver was allocating a dumy page returning it back to the
do_no_page() handler which would the free it immediately. Hopefully
this addresses the main concern there were with this driver in the
past.

The reason for taking the do_no_pfn() approch rather than
remap_pfn_range() is that it needs to benefit from node locality of
the pages on NUMA systems.

While the driver is currently only used on SN2 hardware, it is placed
in drivers/char as it should be possible and beneficial for other
architectures to implement and use the uncached mode.

Please let me know if there are any objections or comments etc. to
this approach. If preferred I can split out the do_no_pfn part into a
seperate patch.

Cheers,
Jes

Signed-off-by: Jes Sorensen <jes@sgi.com>

 drivers/char/Kconfig  |    8 
 drivers/char/Makefile |    1 
 drivers/char/mspec.c  |  442 ++++++++++++++++++++++++++++++++++++++++++++++++++
 include/linux/mm.h    |    1 
 mm/memory.c           |   51 +++++
 5 files changed, 502 insertions(+), 1 deletion(-)

Index: linux-2.6/drivers/char/Kconfig
===================================================================
--- linux-2.6.orig/drivers/char/Kconfig
+++ linux-2.6/drivers/char/Kconfig
@@ -421,6 +421,14 @@
          If you have an SGI Altix with an attached SABrick
          say Y or M here, otherwise say N.
 
+config MSPEC
+	tristate "  Memory special operations driver"
+	depends on IA64
+	help
+	  If you have an ia64 and you want to enable memory special
+	  operations support (formerly known as fetchop), say Y here,
+	  otherwise say N.
+
 source "drivers/serial/Kconfig"
 
 config UNIX98_PTYS
Index: linux-2.6/drivers/char/Makefile
===================================================================
--- linux-2.6.orig/drivers/char/Makefile
+++ linux-2.6/drivers/char/Makefile
@@ -49,6 +49,7 @@
 obj-$(CONFIG_VIOTAPE)		+= viotape.o
 obj-$(CONFIG_HVCS)		+= hvcs.o
 obj-$(CONFIG_SGI_MBCS)		+= mbcs.o
+obj-$(CONFIG_MSPEC)		+= mspec.o
 
 obj-$(CONFIG_PRINTER) += lp.o
 obj-$(CONFIG_TIPAR) += tipar.o
Index: linux-2.6/drivers/char/mspec.c
===================================================================
--- /dev/null
+++ linux-2.6/drivers/char/mspec.c
@@ -0,0 +1,442 @@
+/*
+ * Copyright (C) 2001-2006 Silicon Graphics, Inc.  All rights
+ * reserved.
+ *
+ * This program is free software; you can redistribute it and/or modify it
+ * under the terms of version 2 of the GNU General Public License
+ * as published by the Free Software Foundation.
+ */
+
+/*
+ * SN Platform Special Memory (mspec) Support
+ *
+ * This driver exports the SN special memory (mspec) facility to user
+ * processes.
+ * There are three types of memory made available thru this driver:
+ * fetchops, uncached and cached.
+ *
+ * Fetchops are atomic memory operations that are implemented in the
+ * memory controller on SGI SN hardware.
+ *
+ * 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/config.h>
+#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/proc_fs.h>
+#include <linux/vmalloc.h>
+#include <linux/bitops.h>
+#include <linux/string.h>
+#include <linux/slab.h>
+#include <linux/seq_file.h>
+#include <linux/efi.h>
+#include <linux/numa.h>
+#include <asm/page.h>
+#include <asm/pal.h>
+#include <asm/system.h>
+#include <asm/pgtable.h>
+#include <asm/atomic.h>
+#include <asm/tlbflush.h>
+#include <asm/uncached.h>
+#include <asm/sn/addrs.h>
+#include <asm/sn/arch.h>
+#include <asm/sn/mspec.h>
+#include <asm/sn/sn_cpuid.h>
+#include <asm/sn/io.h>
+#include <asm/sn/bte.h>
+#include <asm/sn/shubio.h>
+
+
+#define FETCHOP_ID	"SGI Fetchop,"
+#define CACHED_ID	"Cached,"
+#define UNCACHED_ID	"Uncached"
+#define REVISION	"4.0"
+#define MSPEC_BASENAME	"mspec"
+
+/*
+ * Page types allocated by the device.
+ */
+enum {
+	MSPEC_FETCHOP = 1,
+	MSPEC_CACHED,
+	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.
+ */
+struct vma_data {
+	atomic_t refcnt;	/* Number of vmas sharing the data. */
+	spinlock_t lock;	/* Serialize access to the vma. */
+	int count;		/* Number of pages allocated. */
+	int type;		/* Type of pages allocated. */
+	unsigned long maddr[0];	/* Array of MSPEC addresses. */
+};
+
+/* used on shub2 to clear FOP cache in the HUB */
+static unsigned long scratch_page[MAX_NUMNODES];
+#define SH2_AMO_CACHE_ENTRIES	4
+
+static inline int
+mspec_zero_block(unsigned long addr, int len)
+{
+	int status;
+
+	if (ia64_platform_is("sn2")) {
+		if (is_shub2()) {
+			int nid;
+			void *p;
+			int i;
+
+			nid = nasid_to_cnodeid(get_node_number(__pa(addr)));
+			p = (void *)TO_AMO(scratch_page[nid]);
+
+			for (i=0; i < SH2_AMO_CACHE_ENTRIES; i++) {
+				FETCHOP_LOAD_OP(p, FETCHOP_LOAD);
+				p += FETCHOP_VAR_SIZE;
+			}
+		}
+
+		status = bte_copy(0, addr & ~__IA64_UNCACHED_OFFSET, len,
+				  BTE_WACQUIRE | BTE_ZERO_FILL, NULL);
+	} else {
+		memset((char *) addr, 0, len);
+		status = 0;
+	}
+	return status;
+}
+
+/*
+ * mspec_open
+ *
+ * Called when a device mapping is created by a means other than mmap
+ * (via fork, 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;
+	atomic_inc(&vdata->refcnt);
+}
+
+/*
+ * mspec_close
+ *
+ * Called when unmapping a device mapping. Frees all mspec pages
+ * belonging to the vma.
+ */
+static void
+mspec_close(struct vm_area_struct *vma)
+{
+	struct vma_data *vdata;
+	int i, pages, result, vdata_size;
+
+	vdata = vma->vm_private_data;
+	if (!atomic_dec_and_test(&vdata->refcnt))
+		return;
+
+	pages = (vma->vm_end - vma->vm_start) >> PAGE_SHIFT;
+	vdata_size = sizeof(struct vma_data) + pages * sizeof(long);
+	for (i = 0; i < pages; i++) {
+		if (vdata->maddr[i] == 0)
+			continue;
+		/*
+		 * Clear the page before sticking it back
+		 * into the pool.
+		 */
+		result = mspec_zero_block(vdata->maddr[i], PAGE_SIZE);
+		if (!result)
+			uncached_free_page(vdata->maddr[i]);
+		else
+			printk(KERN_WARNING "mspec_close(): "
+			       "failed to zero page %i\n",
+			       result);
+	}
+
+	if (vdata_size <= PAGE_SIZE)
+		kfree(vdata);
+	else
+		vfree(vdata);
+}
+
+
+/*
+ * mspec_get_one_pte
+ *
+ * Return the pmd for a given mm and address.
+ */
+static __inline__ pmd_t *
+mspec_get_pmd(struct mm_struct *mm, u64 address)
+{
+	pgd_t *pgd;
+	pud_t *pud;
+	pmd_t *pmd = NULL;
+
+	pgd = pgd_offset(mm, address);
+	if (pgd_present(*pgd)) {
+		pud = pud_offset(pgd, address);
+
+		if (pud_present(*pud))
+			pmd = pmd_offset(pud, address);
+	}
+
+	return pmd;
+}
+
+/*
+ * mspec_nopfn
+ *
+ * Creates a mspec page and maps it to user space.
+ */
+static long
+mspec_nopfn(struct vm_area_struct *vma, unsigned long address, int *unused)
+{
+	unsigned long paddr, maddr;
+	unsigned long pfn;
+	int index;
+	struct vma_data *vdata = vma->vm_private_data;
+
+	index = (address - vma->vm_start) >> PAGE_SHIFT;
+	maddr = (volatile unsigned long) vdata->maddr[index];
+	if (maddr == 0) {
+		maddr = uncached_alloc_page(numa_node_id());
+		if (maddr == 0)
+			return -ENOMEM;
+
+		spin_lock(&vdata->lock);
+		if (vdata->maddr[index] == 0) {
+			vdata->count++;
+			vdata->maddr[index] = maddr;
+		} else {
+			uncached_free_page(maddr);
+			maddr = vdata->maddr[index];
+		}
+		spin_unlock(&vdata->lock);
+	}
+
+	if (vdata->type == MSPEC_FETCHOP)
+		paddr = TO_AMO(maddr);
+	else
+		paddr = __pa(TO_CAC(maddr));
+
+	pfn = paddr >> PAGE_SHIFT;
+
+	return pfn;
+}
+
+static struct vm_operations_struct mspec_vm_ops = {
+	.open = mspec_open,
+	.close = mspec_close,
+	.nopfn = mspec_nopfn
+};
+
+/*
+ * mspec_mmap
+ *
+ * Called when mmaping 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, int 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->vm_end - vma->vm_start) >> PAGE_SHIFT;
+	vdata_size = sizeof(struct vma_data) + pages * sizeof(long);
+	if (vdata_size <= PAGE_SIZE)
+		vdata = kmalloc(vdata_size, GFP_KERNEL);
+	else
+		vdata = vmalloc(vdata_size);
+	if (!vdata)
+		return -ENOMEM;
+	memset(vdata, 0, vdata_size);
+
+	vdata->type = type;
+	spin_lock_init(&vdata->lock);
+	vdata->refcnt = ATOMIC_INIT(1);
+	vma->vm_private_data = vdata;
+
+	vma->vm_flags |= (VM_IO | VM_LOCKED | VM_RESERVED | VM_PFNMAP);
+	if (vdata->type == MSPEC_FETCHOP || vdata->type == MSPEC_UNCACHED)
+		vma->vm_page_prot = pgprot_noncached(vma->vm_page_prot);
+	vma->vm_ops = &mspec_vm_ops;
+
+	return 0;
+}
+
+static int
+fetchop_mmap(struct file *file, struct vm_area_struct *vma)
+{
+	return mspec_mmap(file, vma, MSPEC_FETCHOP);
+}
+
+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 struct file_operations fetchop_fops = {
+	.owner = THIS_MODULE,
+	.mmap = fetchop_mmap
+};
+
+static struct miscdevice fetchop_miscdev = {
+	.minor = MISC_DYNAMIC_MINOR,
+	.name = "sgi_fetchop",
+	.fops = &fetchop_fops
+};
+
+static struct file_operations cached_fops = {
+	.owner = THIS_MODULE,
+	.mmap = cached_mmap
+};
+
+static struct miscdevice cached_miscdev = {
+	.minor = MISC_DYNAMIC_MINOR,
+	.name = "mspec_cached",
+	.fops = &cached_fops
+};
+
+static struct file_operations uncached_fops = {
+	.owner = THIS_MODULE,
+	.mmap = uncached_mmap
+};
+
+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;
+	int nid;
+
+	/*
+	 * The fetchop device only works on SN2 hardware, uncached and cached
+	 * memory drivers should both be valid on all ia64 hardware
+	 */
+	if (ia64_platform_is("sn2")) {
+		if (is_shub2()) {
+			ret = -ENOMEM;
+			for_each_online_node(nid) {
+				int actual_nid;
+
+				scratch_page[nid] = uncached_alloc_page(nid);
+				if (scratch_page[nid] == 0)
+					goto free_scratch_pages;
+				actual_nid = nasid_to_cnodeid(get_node_number(__pa(scratch_page[nid])));
+				if (actual_nid != nid)
+					goto free_scratch_pages;
+			}
+		}
+
+		ret = misc_register(&fetchop_miscdev);
+		if (ret) {
+			printk(KERN_ERR
+			       "%s: failed to register device %i\n",
+			       FETCHOP_ID, ret);
+			goto free_scratch_pages;
+		}
+	}
+	ret = misc_register(&cached_miscdev);
+	if (ret) {
+		printk(KERN_ERR "%s: failed to register device %i\n",
+		       CACHED_ID, ret);
+		misc_deregister(&fetchop_miscdev);
+		goto free_scratch_pages;
+	}
+	ret = misc_register(&uncached_miscdev);
+	if (ret) {
+		printk(KERN_ERR "%s: failed to register device %i\n",
+		       UNCACHED_ID, ret);
+		misc_deregister(&cached_miscdev);
+		misc_deregister(&fetchop_miscdev);
+		goto free_scratch_pages;
+	}
+
+	printk(KERN_INFO "%s %s initialized devices: %s %s %s\n",
+	       MSPEC_BASENAME, REVISION,
+	       ia64_platform_is("sn2") ? FETCHOP_ID : "",
+	       CACHED_ID, UNCACHED_ID);
+
+	return 0;
+
+free_scratch_pages:
+	for_each_node(nid) {
+		if (scratch_page[nid] != 0)
+			uncached_free_page(scratch_page[nid]);
+	}
+	return ret;
+}
+
+static void __exit
+mspec_exit(void)
+{
+	int nid;
+
+	misc_deregister(&uncached_miscdev);
+	misc_deregister(&cached_miscdev);
+	if (ia64_platform_is("sn2")) {
+		misc_deregister(&fetchop_miscdev);
+
+		for_each_node(nid) {
+			if (scratch_page[nid] != 0)
+				uncached_free_page(scratch_page[nid]);
+		}
+	}
+}
+
+module_init(mspec_init);
+module_exit(mspec_exit);
+
+MODULE_AUTHOR("Silicon Graphics, Inc.");
+MODULE_DESCRIPTION("Driver for SGI SN special memory operations");
+MODULE_LICENSE("GPL");
+MODULE_INFO(supported, "external");
Index: linux-2.6/include/linux/mm.h
===================================================================
--- linux-2.6.orig/include/linux/mm.h
+++ linux-2.6/include/linux/mm.h
@@ -199,6 +199,7 @@
 	void (*open)(struct vm_area_struct * area);
 	void (*close)(struct vm_area_struct * area);
 	struct page * (*nopage)(struct vm_area_struct * area, unsigned long address, int *type);
+	long (*nopfn)(struct vm_area_struct * area, unsigned long address, int *type);
 	int (*populate)(struct vm_area_struct * area, unsigned long address, unsigned long len, pgprot_t prot, unsigned long pgoff, int nonblock);
 #ifdef CONFIG_NUMA
 	int (*set_policy)(struct vm_area_struct *vma, struct mempolicy *new);
Index: linux-2.6/mm/memory.c
===================================================================
--- linux-2.6.orig/mm/memory.c
+++ linux-2.6/mm/memory.c
@@ -2148,6 +2148,51 @@
 }
 
 /*
+ * do_no_pfn() tries to create a new page mapping for a page without
+ * a struct_page backing it
+ *
+ * As this is called only for pages that do not currently exist, we
+ * do not need to flush old virtual caches or the TLB.
+ *
+ * We enter with non-exclusive mmap_sem (to exclude vma changes,
+ * but allow concurrent faults), and pte mapped but not yet locked.
+ * We return with mmap_sem still held, but pte unmapped and unlocked.
+ *
+ * It is expected that the ->nopfn handler always returns the same pfn
+ * for a given virtual mapping.
+ */
+static int do_no_pfn(struct mm_struct *mm, struct vm_area_struct *vma,
+		     unsigned long address, pte_t *page_table, pmd_t *pmd,
+		     int write_access)
+{
+	spinlock_t *ptl;
+	pte_t entry;
+	long pfn;
+	int ret = VM_FAULT_MINOR;
+
+	pte_unmap(page_table);
+	BUG_ON(!(vma->vm_flags & VM_PFNMAP));
+
+	pfn = vma->vm_ops->nopfn(vma, address & PAGE_MASK, &ret);
+	if (pfn == -ENOMEM)
+		return VM_FAULT_OOM;
+	if (pfn == -EFAULT)
+		return VM_FAULT_SIGBUS;
+	if (pfn < 0)
+		return VM_FAULT_SIGBUS;
+
+	page_table = pte_offset_map_lock(mm, pmd, address, &ptl);
+
+	entry = pfn_pte(pfn, vma->vm_page_prot);
+	if (write_access)
+		entry = maybe_mkwrite(pte_mkdirty(entry), vma);
+	set_pte_at(mm, address, page_table, entry);
+
+	pte_unmap_unlock(page_table, ptl);
+	return ret;
+}
+
+/*
  * Fault of a previously existing named mapping. Repopulate the pte
  * from the encoded file_pte if possible. This enables swappable
  * nonlinear vmas.
@@ -2209,9 +2254,13 @@
 	old_entry = entry = *pte;
 	if (!pte_present(entry)) {
 		if (pte_none(entry)) {
-			if (!vma->vm_ops || !vma->vm_ops->nopage)
+			if (!vma->vm_ops ||
+			    (!vma->vm_ops->nopage && !vma->vm_ops->nopfn))
 				return do_anonymous_page(mm, vma, address,
 					pte, pmd, write_access);
+			if (vma->vm_ops->nopfn)
+				return do_no_pfn(mm, vma, address,
+						 pte, pmd, write_access);
 			return do_no_page(mm, vma, address,
 					pte, pmd, write_access);
 		}
-
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