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([2a01:e0a:c:37e0:ced3:55bd:f454:e722]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-39c0b7a4294sm14934785f8f.89.2025.04.01.15.38.14 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 01 Apr 2025 15:38:14 -0700 (PDT) Message-ID: <4256338c-e547-4ec5-a72e-262d58f2a818@redhat.com> Date: Wed, 2 Apr 2025 00:38:13 +0200 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v6 4/8] drm/i915/gem: Add i915_gem_object_panic_map() To: =?UTF-8?B?VmlsbGUgU3lyasOkbMOk?= Cc: Jani Nikula , Rodrigo Vivi , Joonas Lahtinen , Tvrtko Ursulin , David Airlie , Simona Vetter , intel-gfx@lists.freedesktop.org, intel-xe@lists.freedesktop.org, dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org References: <20250401125818.333033-1-jfalempe@redhat.com> <20250401125818.333033-5-jfalempe@redhat.com> Content-Language: en-US, fr From: Jocelyn Falempe In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit On 01/04/2025 19:57, Ville Syrjälä wrote: > On Tue, Apr 01, 2025 at 08:47:50PM +0300, Ville Syrjälä wrote: >> On Tue, Apr 01, 2025 at 02:51:10PM +0200, Jocelyn Falempe wrote: >>> Prepare the work for drm_panic support. This is used to map the >>> current framebuffer, so the CPU can overwrite it with the panic >>> message. >>> >>> Signed-off-by: Jocelyn Falempe >>> --- >>> >>> v5: >>> * Use iosys_map for intel_bo_panic_map(). >>> >>> drivers/gpu/drm/i915/display/intel_bo.c | 5 ++++ >>> drivers/gpu/drm/i915/display/intel_bo.h | 1 + >>> drivers/gpu/drm/i915/gem/i915_gem_object.h | 2 ++ >>> drivers/gpu/drm/i915/gem/i915_gem_pages.c | 29 ++++++++++++++++++++++ >>> drivers/gpu/drm/xe/display/intel_bo.c | 10 ++++++++ >>> 5 files changed, 47 insertions(+) >>> >>> diff --git a/drivers/gpu/drm/i915/display/intel_bo.c b/drivers/gpu/drm/i915/display/intel_bo.c >>> index fbd16d7b58d9..ac904e9ec7d5 100644 >>> --- a/drivers/gpu/drm/i915/display/intel_bo.c >>> +++ b/drivers/gpu/drm/i915/display/intel_bo.c >>> @@ -57,3 +57,8 @@ void intel_bo_describe(struct seq_file *m, struct drm_gem_object *obj) >>> { >>> i915_debugfs_describe_obj(m, to_intel_bo(obj)); >>> } >>> + >>> +void intel_bo_panic_map(struct drm_gem_object *obj, struct iosys_map *map) >>> +{ >>> + i915_gem_object_panic_map(to_intel_bo(obj), map); >>> +} >>> diff --git a/drivers/gpu/drm/i915/display/intel_bo.h b/drivers/gpu/drm/i915/display/intel_bo.h >>> index ea7a2253aaa5..5b6c63d99786 100644 >>> --- a/drivers/gpu/drm/i915/display/intel_bo.h >>> +++ b/drivers/gpu/drm/i915/display/intel_bo.h >>> @@ -23,5 +23,6 @@ struct intel_frontbuffer *intel_bo_set_frontbuffer(struct drm_gem_object *obj, >>> struct intel_frontbuffer *front); >>> >>> void intel_bo_describe(struct seq_file *m, struct drm_gem_object *obj); >>> +void intel_bo_panic_map(struct drm_gem_object *obj, struct iosys_map *map); >>> >>> #endif /* __INTEL_BO__ */ >>> diff --git a/drivers/gpu/drm/i915/gem/i915_gem_object.h b/drivers/gpu/drm/i915/gem/i915_gem_object.h >>> index a5f34542135c..b16092707ea5 100644 >>> --- a/drivers/gpu/drm/i915/gem/i915_gem_object.h >>> +++ b/drivers/gpu/drm/i915/gem/i915_gem_object.h >>> @@ -692,6 +692,8 @@ i915_gem_object_unpin_pages(struct drm_i915_gem_object *obj) >>> int __i915_gem_object_put_pages(struct drm_i915_gem_object *obj); >>> int i915_gem_object_truncate(struct drm_i915_gem_object *obj); >>> >>> +void i915_gem_object_panic_map(struct drm_i915_gem_object *obj, struct iosys_map *map); >>> + >>> /** >>> * i915_gem_object_pin_map - return a contiguous mapping of the entire object >>> * @obj: the object to map into kernel address space >>> diff --git a/drivers/gpu/drm/i915/gem/i915_gem_pages.c b/drivers/gpu/drm/i915/gem/i915_gem_pages.c >>> index 8780aa243105..718bea6474d7 100644 >>> --- a/drivers/gpu/drm/i915/gem/i915_gem_pages.c >>> +++ b/drivers/gpu/drm/i915/gem/i915_gem_pages.c >>> @@ -355,6 +355,35 @@ static void *i915_gem_object_map_pfn(struct drm_i915_gem_object *obj, >>> return vaddr ?: ERR_PTR(-ENOMEM); >>> } >>> >>> +/* Map the current framebuffer for CPU access. Called from panic handler, so no >>> + * need to pin or cleanup. >>> + */ >>> +void i915_gem_object_panic_map(struct drm_i915_gem_object *obj, struct iosys_map *map) >>> +{ >>> + enum i915_map_type has_type; >>> + void *ptr; >>> + >>> + ptr = page_unpack_bits(obj->mm.mapping, &has_type); >>> + >>> + >>> + if (!ptr) { >>> + if (i915_gem_object_has_struct_page(obj)) >>> + ptr = i915_gem_object_map_page(obj, I915_MAP_WB); >>> + else >>> + ptr = i915_gem_object_map_pfn(obj, I915_MAP_WB); >> >> WB mapping would require clflushing to make it to the display. >> Is that being done somewhere? > > This also seems to have a bunch of race conditions: > - what happens if the oops happens before the pages have > even been swapped in? > - what happens if the oops happens before we've committed > the fb to the hardware? > The panic handler tries to take the panic_lock from the device->mode_config, which should ensure we're not in the middle of a page swap. https://elixir.bootlin.com/linux/v6.14-rc6/source/include/drm/drm_panic.h#L70 https://elixir.bootlin.com/linux/v6.14-rc6/source/include/drm/drm_mode_config.h#L500 If the lock is already taken when the panic handler run, it will skip this device, and won't draw the panic screen on it. Best regards, -- Jocelyn >> >>> + >>> + if (IS_ERR(ptr)) >>> + return; >> >> What happens when the mapping fails? >> >>> + >>> + obj->mm.mapping = page_pack_bits(ptr, I915_MAP_WB); >>> + } >>> + >>> + if (i915_gem_object_has_iomem(obj)) >>> + iosys_map_set_vaddr_iomem(map, (void __iomem *) ptr); >>> + else >>> + iosys_map_set_vaddr(map, ptr); >>> +} >>> + >>> /* get, pin, and map the pages of the object into kernel space */ >>> void *i915_gem_object_pin_map(struct drm_i915_gem_object *obj, >>> enum i915_map_type type) >>> diff --git a/drivers/gpu/drm/xe/display/intel_bo.c b/drivers/gpu/drm/xe/display/intel_bo.c >>> index 27437c22bd70..c68166a64336 100644 >>> --- a/drivers/gpu/drm/xe/display/intel_bo.c >>> +++ b/drivers/gpu/drm/xe/display/intel_bo.c >>> @@ -59,3 +59,13 @@ void intel_bo_describe(struct seq_file *m, struct drm_gem_object *obj) >>> { >>> /* FIXME */ >>> } >>> + >>> +void intel_bo_panic_map(struct drm_gem_object *obj, struct iosys_map *map) >>> +{ >>> + struct xe_bo *bo = gem_to_xe_bo(obj); >>> + int ret; >>> + >>> + ret = ttm_bo_vmap(&bo->ttm, map); >>> + if (ret) >>> + iosys_map_clear(map); >>> +} >>> -- >>> 2.49.0 >> >> -- >> Ville Syrjälä >> Intel >