[Patch 0/2] ia64 special memory support.

[Patch 0/2] ia64 special memory support.

[Robin Holt]

SGI hardware supports a special type of memory called fetchop or atomic
memory. This memory does atomic operations at the memory controller
instead of using the processor.  It has, however, shown itself to be
slower than the processor since many times that a lock is grabbed,
the cacheline ownership is retained in the processor and the unlock is
nearly free.

This patch set introduces a driver so userland can map these devices
and fault pages of the appropriate type.

Since a typical uncached page does not have a page struct backing it, we
first modify do_no_page to handle a new return type of NOPAGE_FAULTED.
This indicates to the nopage handler that the desired operation is
complete and should be treated as a minor fault.

The second patch introduces the mspec driver.

Thanks, Robin Holt

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[Patch 1/2] Add a NOPAGE_FAULTED flag to do_no_page.

[Robin Holt]

Introduce a NOPAGE_FAULTED flag.  This flag is
returned from a drivers nopage handler to indicate
the desired pte has been inserted and should be handled
as a minor fault.

Signed-off-by: holt@sgi.com


Index: linux-2.6/include/linux/mm.h
===================================================================
--- linux-2.6.orig/include/linux/mm.h	2005-10-11 20:16:07.430703923 -0500
+++ linux-2.6/include/linux/mm.h	2005-10-11 20:16:37.798546969 -0500
@@ -619,6 +619,7 @@ static inline int page_mapped(struct pag
  */
 #define NOPAGE_SIGBUS	(NULL)
 #define NOPAGE_OOM	((struct page *) (-1))
+#define NOPAGE_FAULTED	((struct page *) (-2))
 
 /*
  * Different kinds of faults, as returned by handle_mm_fault().
Index: linux-2.6/mm/memory.c
===================================================================
--- linux-2.6.orig/mm/memory.c	2005-10-11 20:16:09.918718614 -0500
+++ linux-2.6/mm/memory.c	2005-10-11 20:16:37.843464040 -0500
@@ -1862,6 +1862,14 @@ retry:
 		return VM_FAULT_SIGBUS;
 	if (new_page == NOPAGE_OOM)
 		return VM_FAULT_OOM;
+	if (new_page == NOPAGE_FAULTED) {
+		spin_lock(&mm->page_table_lock);
+		page_table = pte_offset_map(pmd, address);
+		pte_unmap(page_table);
+		spin_unlock(&mm->page_table_lock);
+
+		return VM_FAULT_MINOR;
+	}
 
 	/*
 	 * Should we do an early C-O-W break?

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Re: [Patch 0/2] ia64 special memory support.

[Robin Holt]

Introduce the special memory (mspec) driver.  This is used to allow
userland to map fetchop, etc pages

Signed-off-by: holt@sgi.com


Index: linux-2.6/arch/ia64/Kconfig
===================================================================
--- linux-2.6.orig/arch/ia64/Kconfig	2005-10-11 20:16:07.255917963 -0500
+++ linux-2.6/arch/ia64/Kconfig	2005-10-11 20:16:37.573961612 -0500
@@ -231,6 +231,16 @@ config IA64_SGI_SN_XP
 	  this feature will allow for direct communication between SSIs
 	  based on a network adapter and DMA messaging.
 
+config MSPEC
+	tristate "Special Memory support"
+	select IA64_UNCACHED_ALLOCATOR
+	help
+	  This driver allows for cached and uncached mappings of memory
+	  to user processes. On SGI SN hardware it will also export the
+	  special fetchop memory facility.
+	  Fetchops are atomic memory operations that are implemented in the
+	  memory controller on SGI SN hardware.
+
 config FORCE_MAX_ZONEORDER
 	int
 	default "18"
Index: linux-2.6/arch/ia64/kernel/Makefile
===================================================================
--- linux-2.6.orig/arch/ia64/kernel/Makefile	2005-10-11 20:16:07.256894421 -0500
+++ linux-2.6/arch/ia64/kernel/Makefile	2005-10-11 20:16:37.641337219 -0500
@@ -23,6 +23,7 @@ obj-$(CONFIG_IA64_CYCLONE)	+= cyclone.o
 obj-$(CONFIG_CPU_FREQ)		+= cpufreq/
 obj-$(CONFIG_IA64_MCA_RECOVERY)	+= mca_recovery.o
 obj-$(CONFIG_KPROBES)		+= kprobes.o jprobes.o
+obj-$(CONFIG_MSPEC)		+= mspec.o
 obj-$(CONFIG_IA64_UNCACHED_ALLOCATOR)	+= uncached.o
 mca_recovery-y			+= mca_drv.o mca_drv_asm.o
 
Index: linux-2.6/arch/ia64/kernel/mspec.c
===================================================================
--- /dev/null	1970-01-01 00:00:00.000000000 +0000
+++ linux-2.6/arch/ia64/kernel/mspec.c	2005-10-11 21:13:35.807613330 -0500
@@ -0,0 +1,498 @@
+/*
+ * Copyright (C) 2001-2005 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 <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	"Fetchop,"
+#define CACHED_ID	"Cached,"
+#define UNCACHED_ID	"Uncached"
+#define REVISION	"3.0"
+#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. */
+};
+
+/*
+ * Memory Special statistics.
+ */
+struct mspec_stats {
+	atomic_t map_count;	/* Number of active mmap's */
+	atomic_t pages_in_use;	/* Number of mspec pages in use */
+	unsigned long pages_total;	/* Total number of mspec pages */
+};
+
+static struct mspec_stats mspec_stats;
+
+static inline int
+mspec_zero_block(unsigned long addr, int len)
+{
+	int status;
+
+	if (ia64_platform_is("sn2"))
+		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 = vma->vm_private_data;
+	if (atomic_dec_and_test(&vdata->refcnt)) {
+		pages = (vma->vm_end - vma->vm_start) >> PAGE_SHIFT;
+		for (i = 0; i < pages; i++) {
+			if (vdata->maddr[i] != 0) {
+				/*
+				 * 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]);
+					atomic_dec(&mspec_stats.
+						   pages_in_use);
+				} else
+					printk(KERN_WARNING
+					       "mspec_close(): "
+					       "failed to zero page %i\n",
+					       result);
+			}
+		}
+
+		if (vdata->count)
+			atomic_dec(&mspec_stats.map_count);
+		vfree(vdata);
+	}
+}
+
+/*
+ * mspec_get_one_pte
+ *
+ * Return the pte for a given mm and address.
+ */
+static __inline__ int
+mspec_get_one_pte(struct mm_struct *mm, u64 address, pte_t ** page_table)
+{
+	pgd_t *pgd;
+	pmd_t *pmd;
+	pud_t *pud;
+
+	pgd = pgd_offset(mm, address);
+	if (pgd_present(*pgd)) {
+		pud = pud_offset(pgd, address);
+		if (pud_present(*pud)) {
+			pmd = pmd_offset(pud, address);
+			if (pmd_present(*pmd)) {
+				*page_table = pte_offset_map(pmd, address);
+				if (pte_present(**page_table)) {
+					return 0;
+				}
+			}
+		}
+	}
+
+	return -1;
+}
+
+/*
+ * mspec_nopage
+ *
+ * Creates a mspec page and maps it to user space.
+ */
+static struct page *
+mspec_nopage(struct vm_area_struct *vma,
+	     unsigned long address, int *unused)
+{
+	unsigned long paddr, maddr = 0;
+	unsigned long pfn;
+	int index;
+	pte_t *page_table, pte;
+	struct vma_data *vdata = vma->vm_private_data;
+
+	index = (address - vma->vm_start) >> PAGE_SHIFT;
+	if ((volatile unsigned long) vdata->maddr[index] == 0) {
+		maddr = uncached_alloc_page(numa_node_id());
+		if (maddr == 0)
+			return NOPAGE_SIGBUS;	/* NOPAGE_OOM ??? */
+
+		spin_lock(&vdata->lock);
+		if (vdata->maddr[index] == 0) {
+			atomic_inc(&mspec_stats.pages_in_use);
+			vdata->count++;
+
+			vdata->maddr[index] = maddr;
+			maddr = 0;
+		}
+		spin_unlock(&vdata->lock);
+
+		/* Release any unneeded page */
+		if (maddr)
+			uncached_free_page(maddr);
+	}
+
+	spin_lock(&vma->vm_mm->page_table_lock);
+	if (mspec_get_one_pte(vma->vm_mm, address, &page_table) != 0) {
+		if (vdata->type == MSPEC_FETCHOP)
+			paddr = TO_AMO(vdata->maddr[index]);
+		else
+			paddr = __pa(TO_CAC(vdata->maddr[index]));
+
+		pfn = paddr >> PAGE_SHIFT;
+		pte = pfn_pte(pfn, vma->vm_page_prot);
+		pte = pte_mkwrite(pte_mkdirty(pte));
+		set_pte(page_table, pte);
+	}
+	spin_unlock(&vma->vm_mm->page_table_lock);
+
+	return NOPAGE_FAULTED;
+}
+
+static struct vm_operations_struct mspec_vm_ops = {
+	.open mspec_open,
+	.close mspec_close,
+	.nopage mspec_nopage
+};
+
+/*
+ * 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;
+
+	if (vma->vm_pgoff != 0)
+		return -EINVAL;
+
+	if ((vma->vm_flags & VM_WRITE) == 0)
+		return -EPERM;
+
+	pages = (vma->vm_end - vma->vm_start) >> PAGE_SHIFT;
+	if (!
+	    (vdata =
+	     vmalloc(sizeof(struct vma_data) + pages * sizeof(long))))
+		return -ENOMEM;
+	memset(vdata, 0, sizeof(struct vma_data) + pages * sizeof(long));
+
+	vdata->type = type;
+	spin_lock_init(&vdata->lock);
+	vdata->refcnt = ATOMIC_INIT(1);
+	vma->vm_private_data = vdata;
+
+	vma->vm_flags |= (VM_IO | VM_SHM | VM_LOCKED);
+	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;
+
+	atomic_inc(&mspec_stats.map_count);
+	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);
+}
+
+#ifdef CONFIG_PROC_FS
+static void *
+mspec_seq_start(struct seq_file *file, loff_t * offset)
+{
+	if (*offset < MAX_NUMNODES)
+		return offset;
+	return NULL;
+}
+
+static void *
+mspec_seq_next(struct seq_file *file, void *data, loff_t * offset)
+{
+	(*offset)++;
+	if (*offset < MAX_NUMNODES)
+		return offset;
+	return NULL;
+}
+
+static void
+mspec_seq_stop(struct seq_file *file, void *data)
+{
+}
+
+static int
+mspec_seq_show(struct seq_file *file, void *data)
+{
+	int i;
+
+	i = *(loff_t *) data;
+
+	if (!i) {
+		seq_printf(file, "mappings               : %i\n",
+			   atomic_read(&mspec_stats.map_count));
+		seq_printf(file, "current mspec pages    : %i\n",
+			   atomic_read(&mspec_stats.pages_in_use));
+		seq_printf(file, "%4s %7s %7s\n", "node", "total", "free");
+	}
+	return 0;
+}
+
+static struct seq_operations mspec_seq_ops = {
+	.start = mspec_seq_start,
+	.next = mspec_seq_next,
+	.stop = mspec_seq_stop,
+	.show = mspec_seq_show
+};
+
+int
+mspec_proc_open(struct inode *inode, struct file *file)
+{
+	return seq_open(file, &mspec_seq_ops);
+}
+
+static struct file_operations proc_mspec_operations = {
+	.open = mspec_proc_open,
+	.read = seq_read,
+	.llseek = seq_lseek,
+	.release = seq_release,
+};
+
+static struct proc_dir_entry *proc_mspec;
+
+#endif	/* CONFIG_PROC_FS */
+
+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 "sgi_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 "sgi_uncached",
+	.fops & uncached_fops
+};
+
+/*
+ * mspec_init
+ *
+ * Called at boot time to initialize the mspec facility.
+ */
+static int __init
+mspec_init(void)
+{
+	int ret;
+
+	/*
+	 * 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 ((ret = misc_register(&fetchop_miscdev))) {
+			printk(KERN_ERR
+			       "%s: failed to register device %i\n",
+			       FETCHOP_ID, ret);
+			return ret;
+		}
+	}
+	if ((ret = misc_register(&cached_miscdev))) {
+		printk(KERN_ERR "%s: failed to register device %i\n",
+		       CACHED_ID, ret);
+		misc_deregister(&fetchop_miscdev);
+		return ret;
+	}
+	if ((ret = misc_register(&uncached_miscdev))) {
+		printk(KERN_ERR "%s: failed to register device %i\n",
+		       UNCACHED_ID, ret);
+		misc_deregister(&cached_miscdev);
+		misc_deregister(&fetchop_miscdev);
+		return ret;
+	}
+
+	/*
+	 * /proc code needs to be updated to work with the new
+	 * allocation scheme
+	 */
+#ifdef CONFIG_PROC_FS
+	if (!(proc_mspec = create_proc_entry(MSPEC_BASENAME, 0444, NULL))) {
+		printk(KERN_ERR "%s: unable to create proc entry",
+		       MSPEC_BASENAME);
+		misc_deregister(&uncached_miscdev);
+		misc_deregister(&cached_miscdev);
+		misc_deregister(&fetchop_miscdev);
+		return -EINVAL;
+	}
+	proc_mspec->proc_fops = &proc_mspec_operations;
+#endif
+
+	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;
+}
+
+static void __exit
+mspec_exit(void)
+{
+	WARN_ON(atomic_read(&mspec_stats.pages_in_use) > 0);
+
+#ifdef CONFIG_PROC_FS
+	remove_proc_entry(MSPEC_BASENAME, NULL);
+#endif
+	misc_deregister(&uncached_miscdev);
+	misc_deregister(&cached_miscdev);
+	misc_deregister(&fetchop_miscdev);
+}
+
+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");

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