On 2019.04.04 08:30:56 +0100, Chris Wilson wrote:
> ppgtt_free_all_spt() iterates the radixtree as it is deleting it,
> forgoing all protection against the leaves being freed in the process
> (leaving the iter pointing into the void).
>
> A minimal fix seems to be to use the available post_shadow_list to
> decompose the tree into a list prior to destroying the radixtree.
>
> Alerted by the sparse warnings:
>
> drivers/gpu/drm/i915/gvt/gtt.c:757:9: warning: incorrect type in assignment (different address spaces)
> drivers/gpu/drm/i915/gvt/gtt.c:757:9: expected void **slot
> drivers/gpu/drm/i915/gvt/gtt.c:757:9: got void [noderef] <asn:4> **
> drivers/gpu/drm/i915/gvt/gtt.c:757:9: warning: incorrect type in assignment (different address spaces)
> drivers/gpu/drm/i915/gvt/gtt.c:757:9: expected void **slot
> drivers/gpu/drm/i915/gvt/gtt.c:757:9: got void [noderef] <asn:4> **
> drivers/gpu/drm/i915/gvt/gtt.c:758:45: warning: incorrect type in argument 1 (different address spaces)
> drivers/gpu/drm/i915/gvt/gtt.c:758:45: expected void [noderef] <asn:4> **slot
> drivers/gpu/drm/i915/gvt/gtt.c:758:45: got void **slot
> drivers/gpu/drm/i915/gvt/gtt.c:757:9: warning: incorrect type in argument 1 (different address spaces)
> drivers/gpu/drm/i915/gvt/gtt.c:757:9: expected void [noderef] <asn:4> **slot
> drivers/gpu/drm/i915/gvt/gtt.c:757:9: got void **slot
> drivers/gpu/drm/i915/gvt/gtt.c:757:9: warning: incorrect type in assignment (different address spaces)
> drivers/gpu/drm/i915/gvt/gtt.c:757:9: expected void **slot
> drivers/gpu/drm/i915/gvt/gtt.c:757:9: got void [noderef] <asn:4> **
>
> This would also have been loudly warning if run through CI for the
> invalid RCU dereferences.
>
> Fixes: b6c126a39345 ("drm/i915/gvt: Manage shadow pages with radix tree")
> Signed-off-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
> Cc: Changbin Du <changbin.du@xxxxxxxxx>
> Cc: Zhenyu Wang <zhenyuw@xxxxxxxxxxxxxxx>
> Cc: Zhi Wang <zhi.a.wang@xxxxxxxxx>
> ---
> drivers/gpu/drm/i915/gvt/gtt.c | 12 +++++++++---
> 1 file changed, 9 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/gvt/gtt.c b/drivers/gpu/drm/i915/gvt/gtt.c
> index cf133ef03873..9814773882ec 100644
> --- a/drivers/gpu/drm/i915/gvt/gtt.c
> +++ b/drivers/gpu/drm/i915/gvt/gtt.c
> @@ -750,14 +750,20 @@ static void ppgtt_free_spt(struct intel_vgpu_ppgtt_spt *spt)
>
> static void ppgtt_free_all_spt(struct intel_vgpu *vgpu)
> {
> - struct intel_vgpu_ppgtt_spt *spt;
> + struct intel_vgpu_ppgtt_spt *spt, *spn;
> struct radix_tree_iter iter;
> - void **slot;
> + LIST_HEAD(all_spt);
> + void __rcu **slot;
>
> + rcu_read_lock();
> radix_tree_for_each_slot(slot, &vgpu->gtt.spt_tree, &iter, 0) {
> spt = radix_tree_deref_slot(slot);
> - ppgtt_free_spt(spt);
> + list_move(&spt->post_shadow_list, &all_spt);
> }
> + rcu_read_unlock();
> +
> + list_for_each_entry_safe(spt, spn, &all_spt, post_shadow_list)
> + ppgtt_free_spt(spt);
> }
>
As we ensure to flush post shadow list, so this is safe to reuse.
Reviewed-by: Zhenyu Wang <zhenyuw@xxxxxxxxxxxxxxx>
thanks!
> static int ppgtt_handle_guest_write_page_table_bytes(
> --
> 2.20.1
>
--
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