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drm/i915/gtt: Reuse the read-only 64KiB scratch page and directories

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If we can prevent stray writes from landing in the scratch page, we can
reuse the same page and same scratch PT for all contexts without fear of
information leaks and side-channels.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Matthew Auld <matthew.auld@intel.com>
Reviewed-by: Matthew Auld <matthew.auld@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20181029182721.29568-2-chris@chris-wilson.co.uk
This commit is contained in:
Chris Wilson 2018-10-29 18:27:21 +00:00
parent daf3dc0f9b
commit b379e30629
1 changed files with 26 additions and 4 deletions
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30
drivers/gpu/drm/i915/i915_gem_gtt.c
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@ -580,10 +580,9 @@ setup_scratch_page(struct i915_address_space *vm, gfp_t gfp)
* region, including any PTEs which happen to point to scratch.
*
* This is only relevant for the 48b PPGTT where we support
* huge-gtt-pages, see also i915_vma_insert().
*
* TODO: we should really consider write-protecting the scratch-page and
* sharing between ppgtt
* huge-gtt-pages, see also i915_vma_insert(). However, as we share the
* scratch (read-only) between all vm, we create one 64k scratch page
* for all.
*/
size = I915_GTT_PAGE_SIZE_4K;
if (i915_vm_is_48bit(vm) &&
@ -1209,6 +1208,26 @@ static int gen8_init_scratch(struct i915_address_space *vm)
{
int ret;
/*
* If everybody agrees to not to write into the scratch page,
* we can reuse it for all vm, keeping contexts and processes separate.
*/
if (vm->has_read_only &&
vm->i915->kernel_context &&
vm->i915->kernel_context->ppgtt) {
struct i915_address_space *clone =
&vm->i915->kernel_context->ppgtt->vm;
GEM_BUG_ON(!clone->has_read_only);
vm->scratch_page.order = clone->scratch_page.order;
vm->scratch_pte = clone->scratch_pte;
vm->scratch_pt = clone->scratch_pt;
vm->scratch_pd = clone->scratch_pd;
vm->scratch_pdp = clone->scratch_pdp;
return 0;
}
ret = setup_scratch_page(vm, __GFP_HIGHMEM);
if (ret)
return ret;
@ -1289,6 +1308,9 @@ static int gen8_ppgtt_notify_vgt(struct i915_hw_ppgtt *ppgtt, bool create)
static void gen8_free_scratch(struct i915_address_space *vm)
{
if (!vm->scratch_page.daddr)
return;
if (use_4lvl(vm))
free_pdp(vm, vm->scratch_pdp);
free_pd(vm, vm->scratch_pd);