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agp: two-stage page destruction issue

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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>
This commit is contained in:
Jan Beulich
2008-06-18 09:28:00 +01:00
committed by Dave Airlie
parent dcd981a77b
commit da503fa60b
3 changed files with 17 additions and 12 deletions
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16
drivers/char/agp/backend.c
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@@ -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);
}
}