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>

diff --git a/drivers/char/agp/backend.c b/drivers/char/agp/backend.c
index b1bdd01..1ec8710 100644 (file)
--- a/drivers/char/agp/backend.c
+++ b/drivers/char/agp/backend.c
@@ -188,10 +188,10 @@ static int agp_backend_initialize(struct agp_bridge_data *bridge)
 
 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 agp_bridge_data *bridge)
 
        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);
        }
 }
 

diff --git a/drivers/char/agp/generic.c b/drivers/char/agp/generic.c
index 7fc0c99..b6650a6 100644 (file)
--- a/drivers/char/agp/generic.c
+++ b/drivers/char/agp/generic.c
@@ -202,10 +202,13 @@ void agp_free_memory(struct agp_memory *curr)
        }
        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);

diff --git a/drivers/char/agp/intel-agp.c b/drivers/char/agp/intel-agp.c
index eeea50a..01b0340 100644 (file)
--- 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);