From 44c2200afcd59f441b43f27829b4003397cc495d Mon Sep 17 00:00:00 2001 From: Chris Wilson Date: Mon, 19 Oct 2020 21:38:25 +0100 Subject: [PATCH] drm/i915/gem: Flush coherency domains on first set-domain-ioctl MIME-Version: 1.0 Content-Type: text/plain; charset=utf8 Content-Transfer-Encoding: 8bit Avoid skipping what appears to be a no-op set-domain-ioctl if the cache coherency state is inconsistent with our target domain. This also has the utility of using the population of the pages to validate the backing store. The danger in skipping the first set-domain is leaving the cache inconsistent and submitting stale data, or worse leaving the clean data in the cache and not flushing it to the GPU. The impact should be small as it requires a no-op set-domain as the very first ioctl in a particular sequence not found in typical userspace. Reported-by: Zbigniew Kempczyński Fixes: 754a25442705 ("drm/i915: Skip object locking around a no-op set-domain ioctl") Testcase: igt/gem_mmap_offset/blt-coherency Signed-off-by: Chris Wilson Cc: Joonas Lahtinen Cc: Matthew Auld Cc: Zbigniew Kempczyński Cc: # v5.2+ Reviewed-by: Matthew Auld Link: https://patchwork.freedesktop.org/patch/msgid/20201019203825.10966-1-chris@chris-wilson.co.uk --- drivers/gpu/drm/i915/gem/i915_gem_domain.c | 28 +++++++++++++--------------- 1 file changed, 13 insertions(+), 15 deletions(-) diff --git a/drivers/gpu/drm/i915/gem/i915_gem_domain.c b/drivers/gpu/drm/i915/gem/i915_gem_domain.c index 7c90a63..fcce690 100644 --- a/drivers/gpu/drm/i915/gem/i915_gem_domain.c +++ b/drivers/gpu/drm/i915/gem/i915_gem_domain.c @@ -509,21 +509,6 @@ i915_gem_set_domain_ioctl(struct drm_device *dev, void *data, return -ENOENT; /* - * Already in the desired write domain? Nothing for us to do! - * - * We apply a little bit of cunning here to catch a broader set of - * no-ops. If obj->write_domain is set, we must be in the same - * obj->read_domains, and only that domain. Therefore, if that - * obj->write_domain matches the request read_domains, we are - * already in the same read/write domain and can skip the operation, - * without having to further check the requested write_domain. - */ - if (READ_ONCE(obj->write_domain) == read_domains) { - err = 0; - goto out; - } - - /* * Try to flush the object off the GPU without holding the lock. * We will repeat the flush holding the lock in the normal manner * to catch cases where we are gazumped. @@ -560,6 +545,19 @@ i915_gem_set_domain_ioctl(struct drm_device *dev, void *data, if (err) goto out; + /* + * Already in the desired write domain? Nothing for us to do! + * + * We apply a little bit of cunning here to catch a broader set of + * no-ops. If obj->write_domain is set, we must be in the same + * obj->read_domains, and only that domain. Therefore, if that + * obj->write_domain matches the request read_domains, we are + * already in the same read/write domain and can skip the operation, + * without having to further check the requested write_domain. + */ + if (READ_ONCE(obj->write_domain) == read_domains) + goto out_unpin; + err = i915_gem_object_lock_interruptible(obj, NULL); if (err) goto out_unpin; -- 2.7.4