agp: two-stage page destruction issue

agp: two-stage page destruction issue

[Jan Beulich]

Dave,

besides it apparently being useful only in 2.6.24 (the changes in 2.6.25
really mean that it could be converted back to a single-stage mechanism),
I'm seeing an issue in Xen Dom0 kernels, which is caused by the calling
of gart_to_virt() in the second stage invocations of the destroy function.
I think that besides this being a real issue with Xen (where
unmap_page_from_agp() is not just a page table attribute change), this
also is invalid from a theoretical perspective: One should not assume that
gart_to_virt() is still valid after unmapping a page. So minimally (keeping
the 2-stage mechanism) a patch like the one below would be needed.

Jan

--- a/drivers/char/agp/backend.c
+++ b/drivers/char/agp/backend.c
@@ -188,10 +188,10 @@ static int agp_backend_initialize(struct
 
 err_out:
 	if (bridge->driver->needs_scratch_page) {
-		bridge->driver->agp_destroy_page(gart_to_virt(bridge->scratch_page_real),
-						 AGP_PAGE_DESTROY_UNMAP);
-		bridge->driver->agp_destroy_page(gart_to_virt(bridge->scratch_page_real),
-						 AGP_PAGE_DESTROY_FREE);
+		void *va = gart_to_virt(bridge->scratch_page_real);
+
+		bridge->driver->agp_destroy_page(va, AGP_PAGE_DESTROY_UNMAP);
+		bridge->driver->agp_destroy_page(va, AGP_PAGE_DESTROY_FREE);
 	}
 	if (got_gatt)
 		bridge->driver->free_gatt_table(bridge);
@@ -215,10 +215,10 @@ static void agp_backend_cleanup(struct a
 
 	if (bridge->driver->agp_destroy_page &&
 	    bridge->driver->needs_scratch_page) {
-		bridge->driver->agp_destroy_page(gart_to_virt(bridge->scratch_page_real),
-						 AGP_PAGE_DESTROY_UNMAP);
-		bridge->driver->agp_destroy_page(gart_to_virt(bridge->scratch_page_real),
-						 AGP_PAGE_DESTROY_FREE);
+		void *va = gart_to_virt(bridge->scratch_page_real);
+
+		bridge->driver->agp_destroy_page(va, AGP_PAGE_DESTROY_UNMAP);
+		bridge->driver->agp_destroy_page(va, AGP_PAGE_DESTROY_FREE);
 	}
 }
 
--- a/drivers/char/agp/generic.c
+++ b/drivers/char/agp/generic.c
@@ -202,10 +202,13 @@ void agp_free_memory(struct agp_memory *
 	}
 	if (curr->page_count != 0) {
 		for (i = 0; i < curr->page_count; i++) {
-			curr->bridge->driver->agp_destroy_page(gart_to_virt(curr->memory[i]), AGP_PAGE_DESTROY_UNMAP);
+			curr->memory[i] = (unsigned long)gart_to_virt(curr->memory[i]);
+			curr->bridge->driver->agp_destroy_page((void *)curr->memory[i],
+							       AGP_PAGE_DESTROY_UNMAP);
 		}
 		for (i = 0; i < curr->page_count; i++) {
-			curr->bridge->driver->agp_destroy_page(gart_to_virt(curr->memory[i]), AGP_PAGE_DESTROY_FREE);
+			curr->bridge->driver->agp_destroy_page((void *)curr->memory[i],
+							       AGP_PAGE_DESTROY_FREE);
 		}
 	}
 	agp_free_key(curr->key);
--- a/drivers/char/agp/intel-agp.c
+++ b/drivers/char/agp/intel-agp.c
@@ -428,9 +428,11 @@ static void intel_i810_free_by_type(stru
 		if (curr->page_count == 4)
 			i8xx_destroy_pages(gart_to_virt(curr->memory[0]));
 		else {
-			agp_bridge->driver->agp_destroy_page(gart_to_virt(curr->memory[0]),
+			void *va = gart_to_virt(curr->memory[0]);
+
+			agp_bridge->driver->agp_destroy_page(va,
 							     AGP_PAGE_DESTROY_UNMAP);
-			agp_bridge->driver->agp_destroy_page(gart_to_virt(curr->memory[0]),
+			agp_bridge->driver->agp_destroy_page(va,
 							     AGP_PAGE_DESTROY_FREE);
 		}
 		agp_free_page_array(curr);

Re: agp: two-stage page destruction issue

[Dave Airlie]

On Wed, Jun 18, 2008 at 6:28 PM, Jan Beulich <jbeulich@novell.com> wrote:
> Dave,
>
> besides it apparently being useful only in 2.6.24 (the changes in 2.6.25
> really mean that it could be converted back to a single-stage mechanism),
> I'm seeing an issue in Xen Dom0 kernels, which is caused by the calling
> of gart_to_virt() in the second stage invocations of the destroy function.
> I think that besides this being a real issue with Xen (where
> unmap_page_from_agp() is not just a page table attribute change), this
> also is invalid from a theoretical perspective: One should not assume that
> gart_to_virt() is still valid after unmapping a page. So minimally (keeping
> the 2-stage mechanism) a patch like the one below would be needed.
>

Looks good to me, its the simpler change for 2.6.26 at this point.

Dave.

> Jan
>
> --- a/drivers/char/agp/backend.c
> +++ b/drivers/char/agp/backend.c
> @@ -188,10 +188,10 @@ static int agp_backend_initialize(struct
>
>  err_out:
>        if (bridge->driver->needs_scratch_page) {
> -               bridge->driver->agp_destroy_page(gart_to_virt(bridge->scratch_page_real),
> -                                                AGP_PAGE_DESTROY_UNMAP);
> -               bridge->driver->agp_destroy_page(gart_to_virt(bridge->scratch_page_real),
> -                                                AGP_PAGE_DESTROY_FREE);
> +               void *va = gart_to_virt(bridge->scratch_page_real);
> +
> +               bridge->driver->agp_destroy_page(va, AGP_PAGE_DESTROY_UNMAP);
> +               bridge->driver->agp_destroy_page(va, AGP_PAGE_DESTROY_FREE);
>        }
>        if (got_gatt)
>                bridge->driver->free_gatt_table(bridge);
> @@ -215,10 +215,10 @@ static void agp_backend_cleanup(struct a
>
>        if (bridge->driver->agp_destroy_page &&
>            bridge->driver->needs_scratch_page) {
> -               bridge->driver->agp_destroy_page(gart_to_virt(bridge->scratch_page_real),
> -                                                AGP_PAGE_DESTROY_UNMAP);
> -               bridge->driver->agp_destroy_page(gart_to_virt(bridge->scratch_page_real),
> -                                                AGP_PAGE_DESTROY_FREE);
> +               void *va = gart_to_virt(bridge->scratch_page_real);
> +
> +               bridge->driver->agp_destroy_page(va, AGP_PAGE_DESTROY_UNMAP);
> +               bridge->driver->agp_destroy_page(va, AGP_PAGE_DESTROY_FREE);
>        }
>  }
>
> --- a/drivers/char/agp/generic.c
> +++ b/drivers/char/agp/generic.c
> @@ -202,10 +202,13 @@ void agp_free_memory(struct agp_memory *
>        }
>        if (curr->page_count != 0) {
>                for (i = 0; i < curr->page_count; i++) {
> -                       curr->bridge->driver->agp_destroy_page(gart_to_virt(curr->memory[i]), AGP_PAGE_DESTROY_UNMAP);
> +                       curr->memory[i] = (unsigned long)gart_to_virt(curr->memory[i]);
> +                       curr->bridge->driver->agp_destroy_page((void *)curr->memory[i],
> +                                                              AGP_PAGE_DESTROY_UNMAP);
>                }
>                for (i = 0; i < curr->page_count; i++) {
> -                       curr->bridge->driver->agp_destroy_page(gart_to_virt(curr->memory[i]), AGP_PAGE_DESTROY_FREE);
> +                       curr->bridge->driver->agp_destroy_page((void *)curr->memory[i],
> +                                                              AGP_PAGE_DESTROY_FREE);
>                }
>        }
>        agp_free_key(curr->key);
> --- a/drivers/char/agp/intel-agp.c
> +++ b/drivers/char/agp/intel-agp.c
> @@ -428,9 +428,11 @@ static void intel_i810_free_by_type(stru
>                if (curr->page_count == 4)
>                        i8xx_destroy_pages(gart_to_virt(curr->memory[0]));
>                else {
> -                       agp_bridge->driver->agp_destroy_page(gart_to_virt(curr->memory[0]),
> +                       void *va = gart_to_virt(curr->memory[0]);
> +
> +                       agp_bridge->driver->agp_destroy_page(va,
>                                                             AGP_PAGE_DESTROY_UNMAP);
> -                       agp_bridge->driver->agp_destroy_page(gart_to_virt(curr->memory[0]),
> +                       agp_bridge->driver->agp_destroy_page(va,
>                                                             AGP_PAGE_DESTROY_FREE);
>                }
>                agp_free_page_array(curr);
>
>
> --
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Re: agp: two-stage page destruction issue

[Jan Beulich]

>>> "Dave Airlie" <airlied@gmail.com> 19.06.08 01:57 >>>
>On Wed, Jun 18, 2008 at 6:28 PM, Jan Beulich <jbeulich@novell.com> wrote:
>> Dave,
>>
>> besides it apparently being useful only in 2.6.24 (the changes in 2.6.25
>> really mean that it could be converted back to a single-stage mechanism),
>> I'm seeing an issue in Xen Dom0 kernels, which is caused by the calling
>> of gart_to_virt() in the second stage invocations of the destroy function.
>> I think that besides this being a real issue with Xen (where
>> unmap_page_from_agp() is not just a page table attribute change), this
>> also is invalid from a theoretical perspective: One should not assume that
>> gart_to_virt() is still valid after unmapping a page. So minimally (keeping
>> the 2-stage mechanism) a patch like the one below would be needed.
>>
>
>Looks good to me, its the simpler change for 2.6.26 at this point.
>
>Dave.

So if you're considering it even for 2.6.26, will you push it to Linus? That's
how I understand the process would generally work, or should I push it
in this case (in which case it might be good to know whether your above
statement should be translated into an Acked-by or Signed-off-by)?

Thanks, Jan

Re: agp: two-stage page destruction issue

[Dave Airlie]

> 
> So if you're considering it even for 2.6.26, will you push it to Linus? That's
> how I understand the process would generally work, or should I push it
> in this case (in which case it might be good to know whether your above
> statement should be translated into an Acked-by or Signed-off-by)?

Its already pushed :)
http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commit;h=da503fa60b84d5945deb3ab74efdd0bec61df4a1

Dave.