Attachment 48197 Details for Bug 38115 – Prefault all pages before io

[patch] Prefault all pages before io

0001-drm-i915-Prefault-all-pages-for-pread-and-pwrite.patch (text/plain), 2.51 KB, created by Chris Wilson on 2011-06-20 08:42:09 UTC

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Creator: Chris Wilson

Created: 2011-06-20 08:42:09 UTC

Size: 2.51 KB

patch

obsolete

>From 7264f995c1f7ad77db613ed34e13645a8ddf5575 Mon Sep 17 00:00:00 2001
>From: Chris Wilson <chris@chris-wilson.co.uk>
>Date: Mon, 20 Jun 2011 13:29:36 +0100
>Subject: [PATCH] drm/i915: Prefault all pages for pread and pwrite
>
>When using a GTT mapping as a source or destination for the pwrite or
>pread command respectively, unless the PTEs for the GTT vma had been
>prepopulated then get_user_pages() would fail with EFAULT. Usually, we
>only write small amounts of data with pwrite that happened to be
>conveniently prefaulted by the 2-page fault_in_pages_readable. By
>prefaulting all pages before we take the struct mutex, we avoid this
>issue, can stay in the fast path longer and reduce the likelihood of a
>recursive deadlock.
>
>"Fixes" gem_mmap_gtt.
>
>References: https://bugs.freedesktop.org/show_bug.cgi?id=38115
>Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
>---
> drivers/gpu/drm/i915/i915_gem.c |   37 +++++++++++++++++++++++++++++++++----
> 1 files changed, 33 insertions(+), 4 deletions(-)
>
>diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
>index a8579c5..a49db69 100644
>--- a/drivers/gpu/drm/i915/i915_gem.c
>+++ b/drivers/gpu/drm/i915/i915_gem.c
>@@ -560,6 +560,20 @@ out:
> 	return ret;
> }
> 
>+static int prefault_writeable(unsigned long uaddr, unsigned long len)
>+{
>+	/* overflow already checked */
>+	len += uaddr;
>+	while (uaddr < len) {
>+		if (__put_user(0, (char __user *)uaddr))
>+			return -EFAULT;
>+
>+		uaddr += 4096;
>+	}
>+
>+	return 0;
>+}
>+
> /**
>  * Reads data from the object referenced by handle.
>  *
>@@ -581,8 +595,7 @@ i915_gem_pread_ioctl(struct drm_device *dev, void *data,
> 		       args->size))
> 		return -EFAULT;
> 
>-	ret = fault_in_pages_writeable((char __user *)(uintptr_t)args->data_ptr,
>-				       args->size);
>+	ret = prefault_writeable(args->data_ptr, args->size);
> 	if (ret)
> 		return -EFAULT;
> 
>@@ -986,6 +999,23 @@ out:
> 	return ret;
> }
> 
>+static int prefault_readable(unsigned long uaddr, unsigned long len)
>+{
>+	volatile char c;
>+
>+	/* overflow already checked */
>+	len += uaddr;
>+	while (uaddr < len) {
>+		if (__get_user(c, (const char __user *)uaddr))
>+			return -EFAULT;
>+
>+		uaddr += 4096;
>+	}
>+
>+	return 0;
>+	(void)c;
>+}
>+
> /**
>  * Writes data to the object referenced by handle.
>  *
>@@ -1007,8 +1037,7 @@ i915_gem_pwrite_ioctl(struct drm_device *dev, void *data,
> 		       args->size))
> 		return -EFAULT;
> 
>-	ret = fault_in_pages_readable((char __user *)(uintptr_t)args->data_ptr,
>-				      args->size);
>+	ret = prefault_readable(args->data_ptr, args->size);
> 	if (ret)
> 		return -EFAULT;
> 
>-- 
>1.7.5.4
>

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