| Message ID | 20190206130356.18771-30-chris@chris-wilson.co.uk (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | [01/46] drm/i915: Hack and slash, throttle execbuffer hogs | expand |
On 06/02/2019 13:03, Chris Wilson wrote: > An idea for extending uABI inspired by Vulkan's extension chains. > Instead of expanding the data struct for each ioctl every time we need > to add a new feature, define an extension chain instead. As we add > optional interfaces to control the ioctl, we define a new extension > struct that can be linked into the ioctl data only when required by the > user. The key advantage being able to ignore large control structs for > optional interfaces/extensions, while being able to process them in a > consistent manner. > > In comparison to other extensible ioctls, the key difference is the > use of a linked chain of extension structs vs an array of tagged > pointers. For example, > > struct drm_amdgpu_cs_chunk { > __u32 chunk_id; > __u32 length_dw; > __u64 chunk_data; > }; > > struct drm_amdgpu_cs_in { > __u32 ctx_id; > __u32 bo_list_handle; > __u32 num_chunks; > __u32 _pad; > __u64 chunks; > }; > > allows userspace to pass in array of pointers to extension structs, but > must therefore keep constructing that array along side the command stream. > In dynamic situations like that, a linked list is preferred and does not > similar from extra cache line misses as the extension structs themselves > must still be loaded separate to the chunks array. > > v2: Apply the tail call optimisation directly to nip the worry of stack > overflow in the bud. > v3: Defend against recursion. > > Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> > --- > drivers/gpu/drm/i915/Makefile | 1 + > drivers/gpu/drm/i915/i915_user_extensions.c | 43 +++++++++++++++++++++ > drivers/gpu/drm/i915/i915_user_extensions.h | 20 ++++++++++ > drivers/gpu/drm/i915/i915_utils.h | 7 ++++ > include/uapi/drm/i915_drm.h | 20 ++++++++++ > 5 files changed, 91 insertions(+) > create mode 100644 drivers/gpu/drm/i915/i915_user_extensions.c > create mode 100644 drivers/gpu/drm/i915/i915_user_extensions.h > > diff --git a/drivers/gpu/drm/i915/Makefile b/drivers/gpu/drm/i915/Makefile > index a1d834068765..89105b1aaf12 100644 > --- a/drivers/gpu/drm/i915/Makefile > +++ b/drivers/gpu/drm/i915/Makefile > @@ -46,6 +46,7 @@ i915-y := i915_drv.o \ > i915_sw_fence.o \ > i915_syncmap.o \ > i915_sysfs.o \ > + i915_user_extensions.o \ > intel_csr.o \ > intel_device_info.o \ > intel_pm.o \ > diff --git a/drivers/gpu/drm/i915/i915_user_extensions.c b/drivers/gpu/drm/i915/i915_user_extensions.c > new file mode 100644 > index 000000000000..879b4094b2d7 > --- /dev/null > +++ b/drivers/gpu/drm/i915/i915_user_extensions.c > @@ -0,0 +1,43 @@ > +/* > + * SPDX-License-Identifier: MIT > + * > + * Copyright © 2018 Intel Corporation > + */ > + > +#include <linux/sched/signal.h> > +#include <linux/uaccess.h> > +#include <uapi/drm/i915_drm.h> > + > +#include "i915_user_extensions.h" > + > +int i915_user_extensions(struct i915_user_extension __user *ext, > + const i915_user_extension_fn *tbl, > + unsigned long count, > + void *data) > +{ > + unsigned int stackdepth = 512; > + > + while (ext) { > + int err; > + u64 x; > + > + if (!stackdepth--) /* recursion vs useful flexibility */ > + return -EINVAL; I don't get this - which recursion? Variable is also a local automatic. > + > + if (get_user(x, &ext->name)) > + return -EFAULT; > + > + err = -EINVAL; > + if (x < count && tbl[x]) > + err = tbl[x](ext, data); > + if (err) > + return err; Do you plan to add the unwind as previously discussed? Or we define the interface as having undefined state if one extension failed? I would be a bit suboptimal for userspace since it would mean having to throw away and recreate the object in use cases for user extensions capable ioctl is executed post creation of some object. Regards, Tvrtko > + > + if (get_user(x, &ext->next_extension)) > + return -EFAULT; > + > + ext = u64_to_user_ptr(x); > + } > + > + return 0; > +} > diff --git a/drivers/gpu/drm/i915/i915_user_extensions.h b/drivers/gpu/drm/i915/i915_user_extensions.h > new file mode 100644 > index 000000000000..313a510b068a > --- /dev/null > +++ b/drivers/gpu/drm/i915/i915_user_extensions.h > @@ -0,0 +1,20 @@ > +/* > + * SPDX-License-Identifier: MIT > + * > + * Copyright © 2018 Intel Corporation > + */ > + > +#ifndef I915_USER_EXTENSIONS_H > +#define I915_USER_EXTENSIONS_H > + > +struct i915_user_extension; > + > +typedef int (*i915_user_extension_fn)(struct i915_user_extension __user *ext, > + void *data); > + > +int i915_user_extensions(struct i915_user_extension __user *ext, > + const i915_user_extension_fn *tbl, > + unsigned long count, > + void *data); > + > +#endif /* I915_USER_EXTENSIONS_H */ > diff --git a/drivers/gpu/drm/i915/i915_utils.h b/drivers/gpu/drm/i915/i915_utils.h > index 9726df37c4c4..fcc751aa1ea8 100644 > --- a/drivers/gpu/drm/i915/i915_utils.h > +++ b/drivers/gpu/drm/i915/i915_utils.h > @@ -105,6 +105,13 @@ > __T; \ > }) > > +#define container_of_user(ptr, type, member) ({ \ > + void __user *__mptr = (void __user *)(ptr); \ > + BUILD_BUG_ON_MSG(!__same_type(*(ptr), ((type *)0)->member) && \ > + !__same_type(*(ptr), void), \ > + "pointer type mismatch in container_of()"); \ > + ((type __user *)(__mptr - offsetof(type, member))); }) > + > static inline u64 ptr_to_u64(const void *ptr) > { > return (uintptr_t)ptr; > diff --git a/include/uapi/drm/i915_drm.h b/include/uapi/drm/i915_drm.h > index b641c55420b6..be2fcdf3ba90 100644 > --- a/include/uapi/drm/i915_drm.h > +++ b/include/uapi/drm/i915_drm.h > @@ -62,6 +62,26 @@ extern "C" { > #define I915_ERROR_UEVENT "ERROR" > #define I915_RESET_UEVENT "RESET" > > +/* > + * i915_user_extension: Base class for defining a chain of extensions > + * > + * Many interfaces need to grow over time. In most cases we can simply > + * extend the struct and have userspace pass in more data. Another option, > + * as demonstrated by Vulkan's approach to providing extensions for forward > + * and backward compatibility, is to use a list of optional structs to > + * provide those extra details. > + * > + * The key advantage to using an extension chain is that it allows us to > + * redefine the interface more easily than an ever growing struct of > + * increasing complexity, and for large parts of that interface to be > + * entirely optional. The downside is more pointer chasing; chasing across > + * the __user boundary with pointers encapsulated inside u64. > + */ > +struct i915_user_extension { > + __u64 next_extension; > + __u64 name; > +}; > + > /* > * MOCS indexes used for GPU surfaces, defining the cacheability of the > * surface data and the coherency for this data wrt. CPU vs. GPU accesses. >
Quoting Tvrtko Ursulin (2019-02-11 19:00:59) > > On 06/02/2019 13:03, Chris Wilson wrote: > > An idea for extending uABI inspired by Vulkan's extension chains. > > Instead of expanding the data struct for each ioctl every time we need > > to add a new feature, define an extension chain instead. As we add > > optional interfaces to control the ioctl, we define a new extension > > struct that can be linked into the ioctl data only when required by the > > user. The key advantage being able to ignore large control structs for > > optional interfaces/extensions, while being able to process them in a > > consistent manner. > > > > In comparison to other extensible ioctls, the key difference is the > > use of a linked chain of extension structs vs an array of tagged > > pointers. For example, > > > > struct drm_amdgpu_cs_chunk { > > __u32 chunk_id; > > __u32 length_dw; > > __u64 chunk_data; > > }; > > > > struct drm_amdgpu_cs_in { > > __u32 ctx_id; > > __u32 bo_list_handle; > > __u32 num_chunks; > > __u32 _pad; > > __u64 chunks; > > }; > > > > allows userspace to pass in array of pointers to extension structs, but > > must therefore keep constructing that array along side the command stream. > > In dynamic situations like that, a linked list is preferred and does not > > similar from extra cache line misses as the extension structs themselves > > must still be loaded separate to the chunks array. > > > > v2: Apply the tail call optimisation directly to nip the worry of stack > > overflow in the bud. > > v3: Defend against recursion. > > > > Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> > > --- > > drivers/gpu/drm/i915/Makefile | 1 + > > drivers/gpu/drm/i915/i915_user_extensions.c | 43 +++++++++++++++++++++ > > drivers/gpu/drm/i915/i915_user_extensions.h | 20 ++++++++++ > > drivers/gpu/drm/i915/i915_utils.h | 7 ++++ > > include/uapi/drm/i915_drm.h | 20 ++++++++++ > > 5 files changed, 91 insertions(+) > > create mode 100644 drivers/gpu/drm/i915/i915_user_extensions.c > > create mode 100644 drivers/gpu/drm/i915/i915_user_extensions.h > > > > diff --git a/drivers/gpu/drm/i915/Makefile b/drivers/gpu/drm/i915/Makefile > > index a1d834068765..89105b1aaf12 100644 > > --- a/drivers/gpu/drm/i915/Makefile > > +++ b/drivers/gpu/drm/i915/Makefile > > @@ -46,6 +46,7 @@ i915-y := i915_drv.o \ > > i915_sw_fence.o \ > > i915_syncmap.o \ > > i915_sysfs.o \ > > + i915_user_extensions.o \ > > intel_csr.o \ > > intel_device_info.o \ > > intel_pm.o \ > > diff --git a/drivers/gpu/drm/i915/i915_user_extensions.c b/drivers/gpu/drm/i915/i915_user_extensions.c > > new file mode 100644 > > index 000000000000..879b4094b2d7 > > --- /dev/null > > +++ b/drivers/gpu/drm/i915/i915_user_extensions.c > > @@ -0,0 +1,43 @@ > > +/* > > + * SPDX-License-Identifier: MIT > > + * > > + * Copyright © 2018 Intel Corporation > > + */ > > + > > +#include <linux/sched/signal.h> > > +#include <linux/uaccess.h> > > +#include <uapi/drm/i915_drm.h> > > + > > +#include "i915_user_extensions.h" > > + > > +int i915_user_extensions(struct i915_user_extension __user *ext, > > + const i915_user_extension_fn *tbl, > > + unsigned long count, > > + void *data) > > +{ > > + unsigned int stackdepth = 512; > > + > > + while (ext) { > > + int err; > > + u64 x; > > + > > + if (!stackdepth--) /* recursion vs useful flexibility */ > > + return -EINVAL; > > I don't get this - which recursion? Variable is also a local automatic. User recursion: my_uapi_extension = { .name = MY_UAPI_EXTENSION, .next = to_user_pointer(&my_uapi_extension), }; > > + if (get_user(x, &ext->name)) > > + return -EFAULT; > > + > > + err = -EINVAL; > > + if (x < count && tbl[x]) > > + err = tbl[x](ext, data); > > + if (err) > > + return err; > > Do you plan to add the unwind as previously discussed? Or we define the > interface as having undefined state if one extension failed? I would be > a bit suboptimal for userspace since it would mean having to throw away > and recreate the object in use cases for user extensions capable ioctl > is executed post creation of some object. I don't have a nice plan for adding unwind support, and it isn't required to handle the current usecases. Real recursion would do the trick, or manual callstacks. But each unwind callback basically has to handle the struct in an unknown state, and in the end it all boils down to a fini anyway (I think). -Chris
diff --git a/drivers/gpu/drm/i915/Makefile b/drivers/gpu/drm/i915/Makefile index a1d834068765..89105b1aaf12 100644 --- a/drivers/gpu/drm/i915/Makefile +++ b/drivers/gpu/drm/i915/Makefile @@ -46,6 +46,7 @@ i915-y := i915_drv.o \ i915_sw_fence.o \ i915_syncmap.o \ i915_sysfs.o \ + i915_user_extensions.o \ intel_csr.o \ intel_device_info.o \ intel_pm.o \ diff --git a/drivers/gpu/drm/i915/i915_user_extensions.c b/drivers/gpu/drm/i915/i915_user_extensions.c new file mode 100644 index 000000000000..879b4094b2d7 --- /dev/null +++ b/drivers/gpu/drm/i915/i915_user_extensions.c @@ -0,0 +1,43 @@ +/* + * SPDX-License-Identifier: MIT + * + * Copyright © 2018 Intel Corporation + */ + +#include <linux/sched/signal.h> +#include <linux/uaccess.h> +#include <uapi/drm/i915_drm.h> + +#include "i915_user_extensions.h" + +int i915_user_extensions(struct i915_user_extension __user *ext, + const i915_user_extension_fn *tbl, + unsigned long count, + void *data) +{ + unsigned int stackdepth = 512; + + while (ext) { + int err; + u64 x; + + if (!stackdepth--) /* recursion vs useful flexibility */ + return -EINVAL; + + if (get_user(x, &ext->name)) + return -EFAULT; + + err = -EINVAL; + if (x < count && tbl[x]) + err = tbl[x](ext, data); + if (err) + return err; + + if (get_user(x, &ext->next_extension)) + return -EFAULT; + + ext = u64_to_user_ptr(x); + } + + return 0; +} diff --git a/drivers/gpu/drm/i915/i915_user_extensions.h b/drivers/gpu/drm/i915/i915_user_extensions.h new file mode 100644 index 000000000000..313a510b068a --- /dev/null +++ b/drivers/gpu/drm/i915/i915_user_extensions.h @@ -0,0 +1,20 @@ +/* + * SPDX-License-Identifier: MIT + * + * Copyright © 2018 Intel Corporation + */ + +#ifndef I915_USER_EXTENSIONS_H +#define I915_USER_EXTENSIONS_H + +struct i915_user_extension; + +typedef int (*i915_user_extension_fn)(struct i915_user_extension __user *ext, + void *data); + +int i915_user_extensions(struct i915_user_extension __user *ext, + const i915_user_extension_fn *tbl, + unsigned long count, + void *data); + +#endif /* I915_USER_EXTENSIONS_H */ diff --git a/drivers/gpu/drm/i915/i915_utils.h b/drivers/gpu/drm/i915/i915_utils.h index 9726df37c4c4..fcc751aa1ea8 100644 --- a/drivers/gpu/drm/i915/i915_utils.h +++ b/drivers/gpu/drm/i915/i915_utils.h @@ -105,6 +105,13 @@ __T; \ }) +#define container_of_user(ptr, type, member) ({ \ + void __user *__mptr = (void __user *)(ptr); \ + BUILD_BUG_ON_MSG(!__same_type(*(ptr), ((type *)0)->member) && \ + !__same_type(*(ptr), void), \ + "pointer type mismatch in container_of()"); \ + ((type __user *)(__mptr - offsetof(type, member))); }) + static inline u64 ptr_to_u64(const void *ptr) { return (uintptr_t)ptr; diff --git a/include/uapi/drm/i915_drm.h b/include/uapi/drm/i915_drm.h index b641c55420b6..be2fcdf3ba90 100644 --- a/include/uapi/drm/i915_drm.h +++ b/include/uapi/drm/i915_drm.h @@ -62,6 +62,26 @@ extern "C" { #define I915_ERROR_UEVENT "ERROR" #define I915_RESET_UEVENT "RESET" +/* + * i915_user_extension: Base class for defining a chain of extensions + * + * Many interfaces need to grow over time. In most cases we can simply + * extend the struct and have userspace pass in more data. Another option, + * as demonstrated by Vulkan's approach to providing extensions for forward + * and backward compatibility, is to use a list of optional structs to + * provide those extra details. + * + * The key advantage to using an extension chain is that it allows us to + * redefine the interface more easily than an ever growing struct of + * increasing complexity, and for large parts of that interface to be + * entirely optional. The downside is more pointer chasing; chasing across + * the __user boundary with pointers encapsulated inside u64. + */ +struct i915_user_extension { + __u64 next_extension; + __u64 name; +}; + /* * MOCS indexes used for GPU surfaces, defining the cacheability of the * surface data and the coherency for this data wrt. CPU vs. GPU accesses.
An idea for extending uABI inspired by Vulkan's extension chains. Instead of expanding the data struct for each ioctl every time we need to add a new feature, define an extension chain instead. As we add optional interfaces to control the ioctl, we define a new extension struct that can be linked into the ioctl data only when required by the user. The key advantage being able to ignore large control structs for optional interfaces/extensions, while being able to process them in a consistent manner. In comparison to other extensible ioctls, the key difference is the use of a linked chain of extension structs vs an array of tagged pointers. For example, struct drm_amdgpu_cs_chunk { __u32 chunk_id; __u32 length_dw; __u64 chunk_data; }; struct drm_amdgpu_cs_in { __u32 ctx_id; __u32 bo_list_handle; __u32 num_chunks; __u32 _pad; __u64 chunks; }; allows userspace to pass in array of pointers to extension structs, but must therefore keep constructing that array along side the command stream. In dynamic situations like that, a linked list is preferred and does not similar from extra cache line misses as the extension structs themselves must still be loaded separate to the chunks array. v2: Apply the tail call optimisation directly to nip the worry of stack overflow in the bud. v3: Defend against recursion. Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> --- drivers/gpu/drm/i915/Makefile | 1 + drivers/gpu/drm/i915/i915_user_extensions.c | 43 +++++++++++++++++++++ drivers/gpu/drm/i915/i915_user_extensions.h | 20 ++++++++++ drivers/gpu/drm/i915/i915_utils.h | 7 ++++ include/uapi/drm/i915_drm.h | 20 ++++++++++ 5 files changed, 91 insertions(+) create mode 100644 drivers/gpu/drm/i915/i915_user_extensions.c create mode 100644 drivers/gpu/drm/i915/i915_user_extensions.h