[PATCH] drm/i915/gem: Drop relocation support on all new hardware (v4)

[Jason Ekstrand]

The Vulkan driver in Mesa for Intel hardware never uses relocations if
it's running on a version of i915 that supports at least softpin which
all versions of i915 supporting Gen12 do.  On the OpenGL side, Gen12+ is
only supported by iris which never uses relocations.  The older i965
driver in Mesa does use relocations but it only supports Intel hardware
through Gen11 and has been deprecated for all hardware Gen9+.  The
compute driver also never uses relocations.  This only leaves the media
driver which is supposed to be switching to softpin going forward.
Making softpin a requirement for all future hardware seems reasonable.

There is one piece of hardware enabled by default in i915: RKL which was
enabled by e22fa6f0a976 which has not yet landed in drm-next so this
almost but not really a userspace API change for RKL.  If it becomes a
problem, we can always add !IS_ROCKETLAKE(eb->i915) to the condition.

Rejecting relocations starting with newer Gen12 platforms has the
benefit that we don't have to bother supporting it on platforms with
local memory.  Given how much CPU touching of memory is required for
relocations, not having to do so on platforms where not all memory is
directly CPU-accessible carries significant advantages.

v2 (Jason Ekstrand):
 - Allow TGL-LP platforms as they've already shipped

v3 (Jason Ekstrand):
 - WARN_ON platforms with LMEM support in case the check is wrong

v4 (Jason Ekstrand):
 - Call out Rocket Lake in the commit message

Signed-off-by: Jason Ekstrand <jason at jlekstrand.net>
Acked-by: Keith Packard <keithp at keithp.com>
Cc: Dave Airlie <airlied at redhat.com>
Cc: Daniel Vetter <daniel.vetter at intel.com>
---
 drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c | 15 ++++++++++++---
 1 file changed, 12 insertions(+), 3 deletions(-)

diff --git a/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c b/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c
index 99772f37bff60..b02dbd16bfa03 100644
--- a/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c
+++ b/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c
@@ -1764,7 +1764,8 @@ eb_relocate_vma_slow(struct i915_execbuffer *eb, struct eb_vma *ev)
 	return err;
 }
 
-static int check_relocations(const struct drm_i915_gem_exec_object2 *entry)
+static int check_relocations(const struct i915_execbuffer *eb,
+			     const struct drm_i915_gem_exec_object2 *entry)
 {
 	const char __user *addr, *end;
 	unsigned long size;
@@ -1774,6 +1775,14 @@ static int check_relocations(const struct drm_i915_gem_exec_object2 *entry)
 	if (size == 0)
 		return 0;
 
+	/* Relocations are disallowed for all platforms after TGL-LP */
+	if (INTEL_GEN(eb->i915) >= 12 && !IS_TIGERLAKE(eb->i915))
+		return -EINVAL;
+
+	/* All discrete memory platforms are Gen12 or above */
+	if (WARN_ON(HAS_LMEM(eb->i915)))
+		return -EINVAL;
+
 	if (size > N_RELOC(ULONG_MAX))
 		return -EINVAL;
 
@@ -1807,7 +1816,7 @@ static int eb_copy_relocations(const struct i915_execbuffer *eb)
 		if (nreloc == 0)
 			continue;
 
-		err = check_relocations(&eb->exec[i]);
+		err = check_relocations(eb, &eb->exec[i]);
 		if (err)
 			goto err;
 
@@ -1880,7 +1889,7 @@ static int eb_prefault_relocations(const struct i915_execbuffer *eb)
 	for (i = 0; i < count; i++) {
 		int err;
 
-		err = check_relocations(&eb->exec[i]);
+		err = check_relocations(eb, &eb->exec[i]);
 		if (err)
 			return err;
 	}
-- 
2.29.2