From 9ec8795e7d91bc650db03dc6f5315667555dae11 Mon Sep 17 00:00:00 2001 From: Daniel Vetter Date: Thu, 2 Sep 2021 16:20:55 +0200 Subject: [PATCH] drm/i915: Drop __rcu from gem_context->vm MIME-Version: 1.0 Content-Type: text/plain; charset=utf8 Content-Transfer-Encoding: 8bit It's been invariant since commit ccbc1b97948ab671335e950271e39766729736c3 Author: Jason Ekstrand Date: Thu Jul 8 10:48:30 2021 -0500 drm/i915/gem: Don't allow changing the VM on running contexts (v4) this just completes the deed. I've tried to split out prep work for more careful review as much as possible, this is what's left: - get_ppgtt gets simplified since we don't need to grab a temporary reference - we can rely on the temporary reference for the gem_ctx while we inspect the vm. The new vm_id still needs a full i915_vm_open ofc. This also removes the final caller of context_get_vm_rcu - A pile of selftests can now just look at ctx->vm instead of rcu_dereference_protected( , true) or similar things. - All callers of i915_gem_context_vm also disappear. - I've changed the hugepage selftest to set scrub_64K without any locking, because when we inspect that setting we're also not taking any locks either. It works because it's a selftests that's careful (single threaded gives you nice ordering) and not a live driver where races can happen from anywhere. These can only be split up further if we have some intermediate state with a bunch more rcu_dereference_protected(ctx->vm, true), just to shut up lockdep and sparse. The conversion to __rcu happened in commit a4e7ccdac38ec8335d9e4e2656c1a041c77feae1 Author: Chris Wilson Date: Fri Oct 4 14:40:09 2019 +0100 drm/i915: Move context management under GEM Note that we're not breaking the actual bugfix in there: The real bugfix is pushing the i915_vm_relase onto a separate worker, to avoid locking inversion issues. The rcu conversion was just thrown in for entertainment value on top (no vm lookup isn't even close to anything that's a hotpath where removing the single spinlock can be measured). v2: Rebase over the change to move the i915_vm_put() into i915_gem_context_release(). v3: Trivial conflict against repainted shed. Reviewed-by: Maarten Lankhorst Signed-off-by: Daniel Vetter Cc: Jon Bloomfield Cc: Chris Wilson Cc: Maarten Lankhorst Cc: Joonas Lahtinen Cc: Daniel Vetter Cc: "Thomas Hellström" Cc: Matthew Auld Cc: Lionel Landwerlin Cc: Dave Airlie Cc: Jason Ekstrand Link: https://patchwork.freedesktop.org/patch/msgid/20210902142057.929669-9-daniel.vetter@ffwll.ch --- drivers/gpu/drm/i915/gem/i915_gem_context.c | 55 ++----------------- drivers/gpu/drm/i915/gem/i915_gem_context.h | 8 +-- .../gpu/drm/i915/gem/i915_gem_context_types.h | 2 +- .../gpu/drm/i915/gem/selftests/huge_pages.c | 4 +- .../drm/i915/gem/selftests/i915_gem_context.c | 24 +++----- drivers/gpu/drm/i915/i915_trace.h | 2 +- drivers/gpu/drm/i915/selftests/i915_vma.c | 2 +- 7 files changed, 22 insertions(+), 75 deletions(-) diff --git a/drivers/gpu/drm/i915/gem/i915_gem_context.c b/drivers/gpu/drm/i915/gem/i915_gem_context.c index 48ee96bf26438..c2ab0e22db0a2 100644 --- a/drivers/gpu/drm/i915/gem/i915_gem_context.c +++ b/drivers/gpu/drm/i915/gem/i915_gem_context.c @@ -742,44 +742,6 @@ static int set_proto_ctx_param(struct drm_i915_file_private *fpriv, return ret; } -static struct i915_address_space * -context_get_vm_rcu(struct i915_gem_context *ctx) -{ - GEM_BUG_ON(!rcu_access_pointer(ctx->vm)); - - do { - struct i915_address_space *vm; - - /* - * We do not allow downgrading from full-ppgtt [to a shared - * global gtt], so ctx->vm cannot become NULL. - */ - vm = rcu_dereference(ctx->vm); - if (!kref_get_unless_zero(&vm->ref)) - continue; - - /* - * This ppgtt may have be reallocated between - * the read and the kref, and reassigned to a third - * context. In order to avoid inadvertent sharing - * of this ppgtt with that third context (and not - * src), we have to confirm that we have the same - * ppgtt after passing through the strong memory - * barrier implied by a successful - * kref_get_unless_zero(). - * - * Once we have acquired the current ppgtt of ctx, - * we no longer care if it is released from ctx, as - * it cannot be reallocated elsewhere. - */ - - if (vm == rcu_access_pointer(ctx->vm)) - return rcu_pointer_handoff(vm); - - i915_vm_put(vm); - } while (1); -} - static int intel_context_set_gem(struct intel_context *ce, struct i915_gem_context *ctx, struct intel_sseu sseu) @@ -990,7 +952,7 @@ static void i915_gem_context_release_work(struct work_struct *work) if (ctx->syncobj) drm_syncobj_put(ctx->syncobj); - vm = i915_gem_context_vm(ctx); + vm = ctx->vm; if (vm) i915_vm_put(vm); @@ -1216,7 +1178,7 @@ static void context_close(struct i915_gem_context *ctx) set_closed_name(ctx); - vm = i915_gem_context_vm(ctx); + vm = ctx->vm; if (vm) { /* i915_vm_close drops the final reference, which is a bit too * early and could result in surprises with concurrent @@ -1335,7 +1297,7 @@ i915_gem_create_context(struct drm_i915_private *i915, vm = &ppgtt->vm; } if (vm) { - RCU_INIT_POINTER(ctx->vm, i915_vm_open(vm)); + ctx->vm = i915_vm_open(vm); /* i915_vm_open() takes a reference */ i915_vm_put(vm); @@ -1561,15 +1523,12 @@ static int get_ppgtt(struct drm_i915_file_private *file_priv, if (!i915_gem_context_has_full_ppgtt(ctx)) return -ENODEV; - rcu_read_lock(); - vm = context_get_vm_rcu(ctx); - rcu_read_unlock(); - if (!vm) - return -ENODEV; + vm = ctx->vm; + GEM_BUG_ON(!vm); err = xa_alloc(&file_priv->vm_xa, &id, vm, xa_limit_32b, GFP_KERNEL); if (err) - goto err_put; + return err; i915_vm_open(vm); @@ -1577,8 +1536,6 @@ static int get_ppgtt(struct drm_i915_file_private *file_priv, args->value = id; args->size = 0; -err_put: - i915_vm_put(vm); return err; } diff --git a/drivers/gpu/drm/i915/gem/i915_gem_context.h b/drivers/gpu/drm/i915/gem/i915_gem_context.h index c50ded3d1cd31..d3279086a5e7b 100644 --- a/drivers/gpu/drm/i915/gem/i915_gem_context.h +++ b/drivers/gpu/drm/i915/gem/i915_gem_context.h @@ -156,9 +156,9 @@ i915_gem_context_vm(struct i915_gem_context *ctx) static inline bool i915_gem_context_has_full_ppgtt(struct i915_gem_context *ctx) { - GEM_BUG_ON(!!rcu_access_pointer(ctx->vm) != HAS_FULL_PPGTT(ctx->i915)); + GEM_BUG_ON(!!ctx->vm != HAS_FULL_PPGTT(ctx->i915)); - return !!rcu_access_pointer(ctx->vm); + return !!ctx->vm; } static inline struct i915_address_space * @@ -166,12 +166,10 @@ i915_gem_context_get_eb_vm(struct i915_gem_context *ctx) { struct i915_address_space *vm; - rcu_read_lock(); - vm = rcu_dereference(ctx->vm); + vm = ctx->vm; if (!vm) vm = &ctx->i915->ggtt.vm; vm = i915_vm_get(vm); - rcu_read_unlock(); return vm; } diff --git a/drivers/gpu/drm/i915/gem/i915_gem_context_types.h b/drivers/gpu/drm/i915/gem/i915_gem_context_types.h index 0c38789bd4a87..c4617e4d9fa99 100644 --- a/drivers/gpu/drm/i915/gem/i915_gem_context_types.h +++ b/drivers/gpu/drm/i915/gem/i915_gem_context_types.h @@ -262,7 +262,7 @@ struct i915_gem_context { * In other modes, this is a NULL pointer with the expectation that * the caller uses the shared global GTT. */ - struct i915_address_space __rcu *vm; + struct i915_address_space *vm; /** * @pid: process id of creator diff --git a/drivers/gpu/drm/i915/gem/selftests/huge_pages.c b/drivers/gpu/drm/i915/gem/selftests/huge_pages.c index 6c68fe26bb323..5d71626a1ee55 100644 --- a/drivers/gpu/drm/i915/gem/selftests/huge_pages.c +++ b/drivers/gpu/drm/i915/gem/selftests/huge_pages.c @@ -1688,11 +1688,9 @@ int i915_gem_huge_page_live_selftests(struct drm_i915_private *i915) goto out_file; } - mutex_lock(&ctx->mutex); - vm = i915_gem_context_vm(ctx); + vm = ctx->vm; if (vm) WRITE_ONCE(vm->scrub_64K, true); - mutex_unlock(&ctx->mutex); err = i915_subtests(tests, ctx); 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 1536c50144f8a..b32f7fed2d9ce 100644 --- a/drivers/gpu/drm/i915/gem/selftests/i915_gem_context.c +++ b/drivers/gpu/drm/i915/gem/selftests/i915_gem_context.c @@ -27,12 +27,6 @@ #define DW_PER_PAGE (PAGE_SIZE / sizeof(u32)) -static inline struct i915_address_space *ctx_vm(struct i915_gem_context *ctx) -{ - /* single threaded, private ctx */ - return rcu_dereference_protected(ctx->vm, true); -} - static int live_nop_switch(void *arg) { const unsigned int nctx = 1024; @@ -813,7 +807,7 @@ static int igt_shared_ctx_exec(void *arg) struct i915_gem_context *ctx; struct intel_context *ce; - ctx = kernel_context(i915, ctx_vm(parent)); + ctx = kernel_context(i915, parent->vm); if (IS_ERR(ctx)) { err = PTR_ERR(ctx); goto out_test; @@ -823,7 +817,7 @@ static int igt_shared_ctx_exec(void *arg) GEM_BUG_ON(IS_ERR(ce)); if (!obj) { - obj = create_test_object(ctx_vm(parent), + obj = create_test_object(parent->vm, file, &objects); if (IS_ERR(obj)) { err = PTR_ERR(obj); @@ -1380,7 +1374,7 @@ static int igt_ctx_readonly(void *arg) goto out_file; } - vm = ctx_vm(ctx) ?: &i915->ggtt.alias->vm; + vm = ctx->vm ?: &i915->ggtt.alias->vm; if (!vm || !vm->has_read_only) { err = 0; goto out_file; @@ -1499,7 +1493,7 @@ static int write_to_scratch(struct i915_gem_context *ctx, GEM_BUG_ON(offset < I915_GTT_PAGE_SIZE); - err = check_scratch(ctx_vm(ctx), offset); + err = check_scratch(ctx->vm, offset); if (err) return err; @@ -1596,7 +1590,7 @@ static int read_from_scratch(struct i915_gem_context *ctx, GEM_BUG_ON(offset < I915_GTT_PAGE_SIZE); - err = check_scratch(ctx_vm(ctx), offset); + err = check_scratch(ctx->vm, offset); if (err) return err; @@ -1739,7 +1733,7 @@ static int check_scratch_page(struct i915_gem_context *ctx, u32 *out) u32 *vaddr; int err = 0; - vm = ctx_vm(ctx); + vm = ctx->vm; if (!vm) return -ENODEV; @@ -1801,7 +1795,7 @@ static int igt_vm_isolation(void *arg) } /* We can only test vm isolation, if the vm are distinct */ - if (ctx_vm(ctx_a) == ctx_vm(ctx_b)) + if (ctx_a->vm == ctx_b->vm) goto out_file; /* Read the initial state of the scratch page */ @@ -1813,8 +1807,8 @@ static int igt_vm_isolation(void *arg) if (err) goto out_file; - vm_total = ctx_vm(ctx_a)->total; - GEM_BUG_ON(ctx_vm(ctx_b)->total != vm_total); + vm_total = ctx_a->vm->total; + GEM_BUG_ON(ctx_b->vm->total != vm_total); count = 0; num_engines = 0; diff --git a/drivers/gpu/drm/i915/i915_trace.h b/drivers/gpu/drm/i915/i915_trace.h index 806ad688274bf..237e5061381b7 100644 --- a/drivers/gpu/drm/i915/i915_trace.h +++ b/drivers/gpu/drm/i915/i915_trace.h @@ -1246,7 +1246,7 @@ DECLARE_EVENT_CLASS(i915_context, TP_fast_assign( __entry->dev = ctx->i915->drm.primary->index; __entry->ctx = ctx; - __entry->vm = rcu_access_pointer(ctx->vm); + __entry->vm = ctx->vm; ), TP_printk("dev=%u, ctx=%p, ctx_vm=%p", diff --git a/drivers/gpu/drm/i915/selftests/i915_vma.c b/drivers/gpu/drm/i915/selftests/i915_vma.c index 79ba72da08133..1f10fe36619bc 100644 --- a/drivers/gpu/drm/i915/selftests/i915_vma.c +++ b/drivers/gpu/drm/i915/selftests/i915_vma.c @@ -39,7 +39,7 @@ static bool assert_vma(struct i915_vma *vma, { bool ok = true; - if (vma->vm != rcu_access_pointer(ctx->vm)) { + if (vma->vm != ctx->vm) { pr_err("VMA created with wrong VM\n"); ok = false; } -- 2.39.5