PCI: iommu: iotlb flushing

This patch is for batching up the flushing of the IOTLB for the DMAR
implementation found in the Intel VT-d hardware.  It works by building a list
of to be flushed IOTLB entries and a bitmap list of which DMAR engine they are
from.

After either a high water mark (250 accessible via debugfs) or 10ms the list
of iova's will be reclaimed and the DMAR engines associated are IOTLB-flushed.

This approach recovers 15 to 20% of the performance lost when using the IOMMU
for my netperf udp stream benchmark with small packets.  It can be disabled
with a kernel boot parameter "intel_iommu=strict".

Its use does weaken the IOMMU protections a bit.

Signed-off-by: Mark Gross <mgross@linux.intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

2 files changed, 131 insertions, 18 deletions

diff --git a/drivers/pci/intel-iommu.c b/drivers/pci/intel-iommu.c
index 4cb949f0ebd9..8690a0d45d7f 100644
--- a/drivers/pci/intel-iommu.c
+++ b/drivers/pci/intel-iommu.c
@@ -22,6 +22,7 @@
 
 #include <linux/init.h>
 #include <linux/bitmap.h>
+#include <linux/debugfs.h>
 #include <linux/slab.h>
 #include <linux/irq.h>
 #include <linux/interrupt.h>
@@ -31,6 +32,7 @@
 #include <linux/dmar.h>
 #include <linux/dma-mapping.h>
 #include <linux/mempool.h>
+#include <linux/timer.h>
 #include "iova.h"
 #include "intel-iommu.h"
 #include <asm/proto.h> /* force_iommu in this header in x86-64*/
@@ -51,11 +53,32 @@
 
 #define DOMAIN_MAX_ADDR(gaw) ((((u64)1) << gaw) - 1)
 
+
+static void flush_unmaps_timeout(unsigned long data);
+
+DEFINE_TIMER(unmap_timer,  flush_unmaps_timeout, 0, 0);
+
+static struct intel_iommu *g_iommus;
+/* bitmap for indexing intel_iommus */
+static unsigned long    *g_iommus_to_flush;
+static int g_num_of_iommus;
+
+static DEFINE_SPINLOCK(async_umap_flush_lock);
+static LIST_HEAD(unmaps_to_do);
+
+static int timer_on;
+static long list_size;
+static int high_watermark;
+
+static struct dentry *intel_iommu_debug, *debug;
+
+
 static void domain_remove_dev_info(struct dmar_domain *domain);
 
 static int dmar_disabled;
 static int __initdata dmar_map_gfx = 1;
 static int dmar_forcedac;
+static int intel_iommu_strict;
 
 #define DUMMY_DEVICE_DOMAIN_INFO ((struct device_domain_info *)(-1))
 static DEFINE_SPINLOCK(device_domain_lock);
@@ -74,9 +97,13 @@ static int __init intel_iommu_setup(char *str)
                         printk(KERN_INFO
                                 "Intel-IOMMU: disable GFX device mapping\n");
                 } else if (!strncmp(str, "forcedac", 8)) {
-                        printk (KERN_INFO
+                        printk(KERN_INFO
                                 "Intel-IOMMU: Forcing DAC for PCI devices\n");
                         dmar_forcedac = 1;
+                } else if (!strncmp(str, "strict", 6)) {
+                        printk(KERN_INFO
+                                "Intel-IOMMU: disable batched IOTLB flush\n");
+                        intel_iommu_strict = 1;
                 }
 
                 str += strcspn(str, ",");
@@ -966,17 +993,13 @@ static int iommu_init_domains(struct intel_iommu *iommu)
                 set_bit(0, iommu->domain_ids);
         return 0;
 }
-
-static struct intel_iommu *alloc_iommu(struct dmar_drhd_unit *drhd)
+static struct intel_iommu *alloc_iommu(struct intel_iommu *iommu,
+                                        struct dmar_drhd_unit *drhd)
 {
-        struct intel_iommu *iommu;
         int ret;
         int map_size;
         u32 ver;
 
-        iommu = kzalloc(sizeof(*iommu), GFP_KERNEL);
-        if (!iommu)
-                return NULL;
         iommu->reg = ioremap(drhd->reg_base_addr, PAGE_SIZE_4K);
         if (!iommu->reg) {
                 printk(KERN_ERR "IOMMU: can't map the region\n");
@@ -1404,7 +1427,7 @@ static int dmar_pci_device_match(struct pci_dev *devices[], int cnt,
         int index;
 
         while (dev) {
-                for (index = 0; index < cnt; index ++)
+                for (index = 0; index < cnt; index++)
                         if (dev == devices[index])
                                 return 1;
 
@@ -1669,7 +1692,7 @@ int __init init_dmars(void)
         struct dmar_rmrr_unit *rmrr;
         struct pci_dev *pdev;
         struct intel_iommu *iommu;
-        int ret, unit = 0;
+        int nlongs, i, ret, unit = 0;
 
         /*
          * for each drhd
@@ -1680,7 +1703,35 @@ int __init init_dmars(void)
         for_each_drhd_unit(drhd) {
                 if (drhd->ignored)
                         continue;
-                iommu = alloc_iommu(drhd);
+                g_num_of_iommus++;
+                /*
+                 * lock not needed as this is only incremented in the single
+                 * threaded kernel __init code path all other access are read
+                 * only
+                 */
+        }
+
+        nlongs = BITS_TO_LONGS(g_num_of_iommus);
+        g_iommus_to_flush = kzalloc(nlongs * sizeof(unsigned long), GFP_KERNEL);
+        if (!g_iommus_to_flush) {
+                printk(KERN_ERR "Intel-IOMMU: "
+                        "Allocating bitmap array failed\n");
+                return -ENOMEM;
+        }
+
+        g_iommus = kzalloc(g_num_of_iommus * sizeof(*iommu), GFP_KERNEL);
+        if (!g_iommus) {
+                kfree(g_iommus_to_flush);
+                ret = -ENOMEM;
+                goto error;
+        }
+
+        i = 0;
+        for_each_drhd_unit(drhd) {
+                if (drhd->ignored)
+                        continue;
+                iommu = alloc_iommu(&g_iommus[i], drhd);
+                i++;
                 if (!iommu) {
                         ret = -ENOMEM;
                         goto error;
@@ -1713,7 +1764,6 @@ int __init init_dmars(void)
          * endfor
          */
         for_each_rmrr_units(rmrr) {
-                int i;
                 for (i = 0; i < rmrr->devices_cnt; i++) {
                         pdev = rmrr->devices[i];
                         /* some BIOS lists non-exist devices in DMAR table */
@@ -1769,6 +1819,7 @@ error:
                 iommu = drhd->iommu;
                 free_iommu(iommu);
         }
+        kfree(g_iommus);
         return ret;
 }
 
@@ -1917,6 +1968,53 @@ error:
         return 0;
 }
 
+static void flush_unmaps(void)
+{
+        struct iova *node, *n;
+        unsigned long flags;
+        int i;
+
+        spin_lock_irqsave(&async_umap_flush_lock, flags);
+        timer_on = 0;
+
+        /* just flush them all */
+        for (i = 0; i < g_num_of_iommus; i++) {
+                if (test_and_clear_bit(i, g_iommus_to_flush))
+                        iommu_flush_iotlb_global(&g_iommus[i], 0);
+        }
+
+        list_for_each_entry_safe(node, n, &unmaps_to_do, list) {
+                /* free iova */
+                list_del(&node->list);
+                __free_iova(&((struct dmar_domain *)node->dmar)->iovad, node);
+
+        }
+        list_size = 0;
+        spin_unlock_irqrestore(&async_umap_flush_lock, flags);
+}
+
+static void flush_unmaps_timeout(unsigned long data)
+{
+        flush_unmaps();
+}
+
+static void add_unmap(struct dmar_domain *dom, struct iova *iova)
+{
+        unsigned long flags;
+
+        spin_lock_irqsave(&async_umap_flush_lock, flags);
+        iova->dmar = dom;
+        list_add(&iova->list, &unmaps_to_do);
+        set_bit((dom->iommu - g_iommus), g_iommus_to_flush);
+
+        if (!timer_on) {
+                mod_timer(&unmap_timer, jiffies + msecs_to_jiffies(10));
+                timer_on = 1;
+        }
+        list_size++;
+        spin_unlock_irqrestore(&async_umap_flush_lock, flags);
+}
+
 static void intel_unmap_single(struct device *dev, dma_addr_t dev_addr,
         size_t size, int dir)
 {
@@ -1944,13 +2042,21 @@ static void intel_unmap_single(struct device *dev, dma_addr_t dev_addr,
         dma_pte_clear_range(domain, start_addr, start_addr + size);
         /* free page tables */
         dma_pte_free_pagetable(domain, start_addr, start_addr + size);
-
-        if (iommu_flush_iotlb_psi(domain->iommu, domain->id, start_addr,
-                        size >> PAGE_SHIFT_4K, 0))
-                iommu_flush_write_buffer(domain->iommu);
-
-        /* free iova */
-        __free_iova(&domain->iovad, iova);
+        if (intel_iommu_strict) {
+                if (iommu_flush_iotlb_psi(domain->iommu,
+                        domain->id, start_addr, size >> PAGE_SHIFT_4K, 0))
+                        iommu_flush_write_buffer(domain->iommu);
+                /* free iova */
+                __free_iova(&domain->iovad, iova);
+        } else {
+                add_unmap(domain, iova);
+                /*
+                 * queue up the release of the unmap to save the 1/6th of the
+                 * cpu used up by the iotlb flush operation...
+                 */
+                if (list_size > high_watermark)
+                        flush_unmaps();
+        }
 }
 
 static void * intel_alloc_coherent(struct device *hwdev, size_t size,
@@ -2274,6 +2380,10 @@ int __init intel_iommu_init(void)
         if (dmar_table_init())
                 return  -ENODEV;
 
+        high_watermark = 250;
+        intel_iommu_debug = debugfs_create_dir("intel_iommu", NULL);
+        debug = debugfs_create_u32("high_watermark", S_IWUGO | S_IRUGO,
+                                        intel_iommu_debug, &high_watermark);
         iommu_init_mempool();
         dmar_init_reserved_ranges();
 
@@ -2289,6 +2399,7 @@ int __init intel_iommu_init(void)
         printk(KERN_INFO
         "PCI-DMA: Intel(R) Virtualization Technology for Directed I/O\n");
 
+        init_timer(&unmap_timer);
         force_iommu = 1;
         dma_ops = &intel_dma_ops;
         return 0;
diff --git a/drivers/pci/iova.h b/drivers/pci/iova.h
index 228f6c94b69c..2f1317801b20 100644
--- a/drivers/pci/iova.h
+++ b/drivers/pci/iova.h
@@ -24,6 +24,8 @@ struct iova {
         struct rb_node  node;
         unsigned long   pfn_hi; /* IOMMU dish out addr hi */
         unsigned long   pfn_lo; /* IOMMU dish out addr lo */
+        struct list_head list;
+        void *dmar;
 };
 
 /* holds all the iova translations for a domain */