Re: [Intel-gfx] [PATCH 07/11] drm/i915: Add i915_gem_context_is_full_ppgtt

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On 02/09/2021 16:22, Daniel Vetter wrote:
On Thu, Sep 02, 2021 at 03:54:36PM +0100, Tvrtko Ursulin wrote:
On 02/09/2021 15:20, Daniel Vetter wrote:
And use it anywhere we have open-coded checks for ctx->vm that really
only check for full ppgtt.

Plus for paranoia add a GEM_BUG_ON that checks it's really only set
when we have full ppgtt, just in case. gem_context->vm is different
since it's NULL in ggtt mode, unlike intel_context->vm or gt->vm,
which is always set.

v2: 0day found a testcase that I missed.

Reviewed-by: Maarten Lankhorst <maarten.lankhorst@xxxxxxxxxxxxxxx>
Signed-off-by: Daniel Vetter <daniel.vetter@xxxxxxxxx>
Cc: Jon Bloomfield <jon.bloomfield@xxxxxxxxx>
Cc: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
Cc: Maarten Lankhorst <maarten.lankhorst@xxxxxxxxxxxxxxx>
Cc: Joonas Lahtinen <joonas.lahtinen@xxxxxxxxxxxxxxx>
Cc: Daniel Vetter <daniel.vetter@xxxxxxxx>
Cc: "Thomas Hellström" <thomas.hellstrom@xxxxxxxxxxxxxxx>
Cc: Matthew Auld <matthew.auld@xxxxxxxxx>
Cc: Lionel Landwerlin <lionel.g.landwerlin@xxxxxxxxx>
Cc: Dave Airlie <airlied@xxxxxxxxxx>
Cc: Jason Ekstrand <jason@xxxxxxxxxxxxxx>
---
   drivers/gpu/drm/i915/gem/i915_gem_context.c           | 2 +-
   drivers/gpu/drm/i915/gem/i915_gem_context.h           | 7 +++++++
   drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c        | 2 +-
   drivers/gpu/drm/i915/gem/selftests/i915_gem_context.c | 6 +++---
   4 files changed, 12 insertions(+), 5 deletions(-)

diff --git a/drivers/gpu/drm/i915/gem/i915_gem_context.c b/drivers/gpu/drm/i915/gem/i915_gem_context.c
index 7a566fb7cca4..1eec85944c1f 100644
--- a/drivers/gpu/drm/i915/gem/i915_gem_context.c
+++ b/drivers/gpu/drm/i915/gem/i915_gem_context.c
@@ -1566,7 +1566,7 @@ static int get_ppgtt(struct drm_i915_file_private *file_priv,
   	int err;
   	u32 id;
-	if (!rcu_access_pointer(ctx->vm))
+	if (!i915_gem_context_is_full_ppgtt(ctx))

It reads a bit wrong because GEM context cannot *be* full ppggt. It can be
associated with a VM which is or isn't full ppgtt. So a test on a VM
retrieved from a context is semnntically more correct. Perhaps you want to
consider adding a helper to that effect instead? It could mean splitting
into two helpers (getter + test) or maybe just renaming would work. Like
i915_gem_context_has_full_ppgtt_vm(ctx)?

The pointer isn't set when the driver/context isn't running in full ppgtt
mode. This is why I've added the GEM_BUG_ON to check we're not breaking
any invariants. So yeah it is a full ppgtt context or it's not, that is
indeed the question here.

I'm happy to bikeshed the naming, but I don't see how your suggestion is
an improvement.

I think the pointer being set or not is implementation detail, for instance we could have it always set just like it is in intel_context.

I simply think GEM context *isn't* full ppgtt, but the VM is. And since GEM context *points* to a VM, *has* is the right verb in my mind. You did not write why do you not see has as more correct than is so I don't want to be guessing too much.

Regards,

Tvrtko


Regards,

Tvrtko

   		return -ENODEV;
   	rcu_read_lock();
diff --git a/drivers/gpu/drm/i915/gem/i915_gem_context.h b/drivers/gpu/drm/i915/gem/i915_gem_context.h
index da6e8b506d96..37536a260e6e 100644
--- a/drivers/gpu/drm/i915/gem/i915_gem_context.h
+++ b/drivers/gpu/drm/i915/gem/i915_gem_context.h
@@ -154,6 +154,13 @@ i915_gem_context_vm(struct i915_gem_context *ctx)
   	return rcu_dereference_protected(ctx->vm, lockdep_is_held(&ctx->mutex));
   }
+static inline bool i915_gem_context_is_full_ppgtt(struct i915_gem_context *ctx)
+{
+	GEM_BUG_ON(!!rcu_access_pointer(ctx->vm) != HAS_FULL_PPGTT(ctx->i915));
+
+	return !!rcu_access_pointer(ctx->vm);
+}
+
   static inline struct i915_address_space *
   i915_gem_context_get_eb_vm(struct i915_gem_context *ctx)
   {
diff --git a/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c b/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c
index 905b1cbd22d5..40f08948f0b2 100644
--- a/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c
+++ b/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c
@@ -749,7 +749,7 @@ static int eb_select_context(struct i915_execbuffer *eb)
   		return PTR_ERR(ctx);
   	eb->gem_context = ctx;
-	if (rcu_access_pointer(ctx->vm))
+	if (i915_gem_context_is_full_ppgtt(ctx))
   		eb->invalid_flags |= EXEC_OBJECT_NEEDS_GTT;
   	return 0;
diff --git a/drivers/gpu/drm/i915/gem/selftests/i915_gem_context.c b/drivers/gpu/drm/i915/gem/selftests/i915_gem_context.c
index fc7fb33a3a52..947154e445a7 100644
--- a/drivers/gpu/drm/i915/gem/selftests/i915_gem_context.c
+++ b/drivers/gpu/drm/i915/gem/selftests/i915_gem_context.c
@@ -704,7 +704,7 @@ static int igt_ctx_exec(void *arg)
   				pr_err("Failed to fill dword %lu [%lu/%lu] with gpu (%s) [full-ppgtt? %s], err=%d\n",
   				       ndwords, dw, max_dwords(obj),
   				       engine->name,
-				       yesno(!!rcu_access_pointer(ctx->vm)),
+				       yesno(i915_gem_context_is_full_ppgtt(ctx)),
   				       err);
   				intel_context_put(ce);
   				kernel_context_close(ctx);
@@ -838,7 +838,7 @@ static int igt_shared_ctx_exec(void *arg)
   				pr_err("Failed to fill dword %lu [%lu/%lu] with gpu (%s) [full-ppgtt? %s], err=%d\n",
   				       ndwords, dw, max_dwords(obj),
   				       engine->name,
-				       yesno(!!rcu_access_pointer(ctx->vm)),
+				       yesno(i915_gem_context_is_full_ppgtt(ctx)),
   				       err);
   				intel_context_put(ce);
   				kernel_context_close(ctx);
@@ -1417,7 +1417,7 @@ static int igt_ctx_readonly(void *arg)
   				pr_err("Failed to fill dword %lu [%lu/%lu] with gpu (%s) [full-ppgtt? %s], err=%d\n",
   				       ndwords, dw, max_dwords(obj),
   				       ce->engine->name,
-				       yesno(!!ctx_vm(ctx)),
+				       yesno(i915_gem_context_is_full_ppgtt(ctx)),
   				       err);
   				i915_gem_context_unlock_engines(ctx);
   				goto out_file;





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