agp: two-stage page destruction issue

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

Signed-off-by: Dave Airlie <airlied@redhat.com>

1 files changed, 4 insertions, 2 deletions

diff --git a/drivers/char/agp/intel-agp.c b/drivers/char/agp/intel-agp.c
index eeea50a1d22a..01b03402ea92 100644
--- a/drivers/char/agp/intel-agp.c
+++ b/drivers/char/agp/intel-agp.c
@@ -418,9 +418,11 @@ static void intel_i810_free_by_type(struct agp_memory *curr)
                 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);