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SubjectRe: [PATCH]intel-iommu batched iotlb flushes
On Mon, 11 Feb 2008 14:41:05 -0800 mark gross wrote:

> The hole is the following scenarios:
> do many map_signal operations, do some unmap_signals, reuse a recently
> unmapped page, <errant DMA hardware sneaks through and steps on reused
> memory>
>
> Or: you have rouge hardware using DMA's to look at pages: do many

or rogue hardware?

> map_signal's, do many unmap_singles, reuse some unmapped pages :

signal .................... single
> <rouge hardware looks at reused page>

why rouge?

> Note : these holes are very hard to get too, as the IOTLB is small and
> only the PTE's still in the IOTLB can be accessed through this
> mechanism.
>
> Its recommended that strict is used when developing drivers that do DMA
> operations to catch bugs early. For production code where performance
> is desired running with the batched IOTLB flushing is a good way to
> go.
>
>
> --mgross
>
>
> Signed-off-by: <mgross@linux.intel.com>
>
>
>
> Index: linux-2.6.24-mm1/drivers/pci/intel-iommu.c
> ===================================================================
> --- linux-2.6.24-mm1.orig/drivers/pci/intel-iommu.c 2008-02-07 13:03:10.000000000 -0800
> +++ linux-2.6.24-mm1/drivers/pci/intel-iommu.c 2008-02-11 10:38:49.000000000 -0800

> @@ -50,11 +52,39 @@
>
> #define DOMAIN_MAX_ADDR(gaw) ((((u64)1) << gaw) - 1)
>
> +
> +static void flush_unmaps_timeout(unsigned long data);
> +
> +static struct timer_list unmap_timer =
> + TIMER_INITIALIZER(flush_unmaps_timeout, 0, 0);
> +
> +struct unmap_list {
> + struct list_head list;
> + struct dmar_domain *domain;
> + struct iova *iova;
> +};
> +
> +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);
> @@ -73,9 +103,13 @@
> 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", 8)) {
> + printk(KERN_INFO
> + "Intel-IOMMU: disable bached IOTLB flush\n");

batched

> + intel_iommu_strict = 1;
> }
>
> str += strcspn(str, ",");

> @@ -1672,7 +1702,29 @@
> for_each_drhd_unit(drhd) {
> if (drhd->ignored)
> continue;
> - iommu = alloc_iommu(drhd);
> + g_num_of_iommus++;
> + }
> +
> + 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 "Allocating bitmap array failed\n");

identify: "IOMMU:

> + 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;

> Index: linux-2.6.24-mm1/Documentation/kernel-parameters.txt
> ===================================================================
> --- linux-2.6.24-mm1.orig/Documentation/kernel-parameters.txt 2008-02-11 13:44:23.000000000 -0800
> +++ linux-2.6.24-mm1/Documentation/kernel-parameters.txt 2008-02-11 14:23:37.000000000 -0800
> @@ -822,6 +822,10 @@
> than 32 bit addressing. The default is to look
> for translation below 32 bit and if not available
> then look in the higher range.
> + strict [Default Off]
> + With this option on every umap_signle will

on, every unmap_si{ngle,gnal} ??
> + result in a hardware IOTLB flush opperation as
> + opposed to batching them for performance.
>
> io_delay= [X86-32,X86-64] I/O delay method
> 0x80


---
~Randy

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