[Intel-gfx] [PATCH v4 4/4] drm/i915/selftest: Clear the output buffers before GPU writes

[Ramalingam C]

From: Chris Wilson <ch...@chris-wilson.co.uk>

When testing whether we can get the GPU to leak information about
non-privileged state, we first need to ensure that the output buffer is
set to a known value as the HW may opt to skip the write into memory for
a non-privileged read of a sensitive register. We chose POISON_INUSE (0x5a)
so that is both non-zero and distinct from the poison values used during
the test.

v2:
  Use i915_gem_object_pin_map_unlocked

Reported-by: CQ Tang <cq.t...@intel.com>
Signed-off-by: Chris Wilson <ch...@chris-wilson.co.uk>
Cc: CQ Tang <cq.t...@intel.com>
cc: Joonas Lahtinen <joonas.lahti...@linux.intel.com>
Signed-off-by: Ramalingam C <ramalinga...@intel.com>
Reviewed-by: Thomas Hellstrom <thomas.hellst...@linux.intel.com>
---
 drivers/gpu/drm/i915/gt/selftest_lrc.c | 32 ++++++++++++++++++++++----
 1 file changed, 28 insertions(+), 4 deletions(-)

diff --git a/drivers/gpu/drm/i915/gt/selftest_lrc.c 
b/drivers/gpu/drm/i915/gt/selftest_lrc.c
index e4d5d74489bf..d04d08d9d92e 100644
--- a/drivers/gpu/drm/i915/gt/selftest_lrc.c
+++ b/drivers/gpu/drm/i915/gt/selftest_lrc.c
@@ -1395,6 +1395,30 @@ static int compare_isolation(struct intel_engine_cs 
*engine,
        return err;
 }
 
+static struct i915_vma *
+create_result_vma(struct i915_address_space *vm, unsigned long sz)
+{
+       struct i915_vma *vma;
+       void *ptr;
+
+       vma = create_user_vma(vm, sz);
+       if (IS_ERR(vma))
+               return vma;
+
+       /* Set the results to a known value distinct from the poison */
+       ptr = i915_gem_object_pin_map_unlocked(vma->obj, I915_MAP_WC);
+       if (IS_ERR(ptr)) {
+               i915_vma_put(vma);
+               return ERR_CAST(ptr);
+       }
+
+       memset(ptr, POISON_INUSE, vma->size);
+       i915_gem_object_flush_map(vma->obj);
+       i915_gem_object_unpin_map(vma->obj);
+
+       return vma;
+}
+
 static int __lrc_isolation(struct intel_engine_cs *engine, u32 poison)
 {
        u32 *sema = memset32(engine->status_page.addr + 1000, 0, 1);
@@ -1413,13 +1437,13 @@ static int __lrc_isolation(struct intel_engine_cs 
*engine, u32 poison)
                goto err_A;
        }
 
-       ref[0] = create_user_vma(A->vm, SZ_64K);
+       ref[0] = create_result_vma(A->vm, SZ_64K);
        if (IS_ERR(ref[0])) {
                err = PTR_ERR(ref[0]);
                goto err_B;
        }
 
-       ref[1] = create_user_vma(A->vm, SZ_64K);
+       ref[1] = create_result_vma(A->vm, SZ_64K);
        if (IS_ERR(ref[1])) {
                err = PTR_ERR(ref[1]);
                goto err_ref0;
@@ -1441,13 +1465,13 @@ static int __lrc_isolation(struct intel_engine_cs 
*engine, u32 poison)
        }
        i915_request_put(rq);
 
-       result[0] = create_user_vma(A->vm, SZ_64K);
+       result[0] = create_result_vma(A->vm, SZ_64K);
        if (IS_ERR(result[0])) {
                err = PTR_ERR(result[0]);
                goto err_ref1;
        }
 
-       result[1] = create_user_vma(A->vm, SZ_64K);
+       result[1] = create_result_vma(A->vm, SZ_64K);
        if (IS_ERR(result[1])) {
                err = PTR_ERR(result[1]);
                goto err_result0;
-- 
2.20.1