Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
Date:   Wed, 21 Jun 2023 11:09:31 +0300
From:   Pekka Paalanen <ppaalanen@gmail.com>
To:     =?UTF-8?B?QW5kcsOp?= Almeida <andrealmeid@igalia.com>
Cc:     dri-devel@lists.freedesktop.org, amd-gfx@lists.freedesktop.org,
        linux-kernel@vger.kernel.org, kernel-dev@igalia.com,
        alexander.deucher@amd.com, christian.koenig@amd.com,
        pierre-eric.pelloux-prayer@amd.com,
        Simon Ser <contact@emersion.fr>,
        Rob Clark <robdclark@gmail.com>,
        Daniel Vetter <daniel@ffwll.ch>,
        Daniel Stone <daniel@fooishbar.org>,
        'Marek =?UTF-8?B?T2zFocOhayc=?= <maraeo@gmail.com>,
        Dave Airlie <airlied@gmail.com>,
        Michel =?UTF-8?B?RMOkbnplcg==?= <michel.daenzer@mailbox.org>,
        Samuel Pitoiset <samuel.pitoiset@gmail.com>,
        Timur =?UTF-8?B?S3Jpc3TDs2Y=?= <timur.kristof@gmail.com>,
        Bas Nieuwenhuizen <bas@basnieuwenhuizen.nl>
Subject: Re: [RFC PATCH v3 2/4] drm: Create DRM_IOCTL_GET_RESET
Message-ID: <20230621110931.6f3c8914@eldfell>
In-Reply-To: <20230621005719.836857-3-andrealmeid@igalia.com>
References: <20230621005719.836857-1-andrealmeid@igalia.com>
        <20230621005719.836857-3-andrealmeid@igalia.com>
MIME-Version: 1.0
Content-Type: multipart/signed; boundary="Sig_/ATv9R6N/IyatZ_qIv8rdPJF";
 protocol="application/pgp-signature"; micalg=pgp-sha256
Precedence: bulk

--Sig_/ATv9R6N/IyatZ_qIv8rdPJF
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: quoted-printable

On Tue, 20 Jun 2023 21:57:17 -0300
Andr=C3=A9 Almeida <andrealmeid@igalia.com> wrote:

> Create a new DRM ioctl operation to get the numbers of resets for a
> given context. The numbers reflect just the resets that happened after
> the context was created, and not since the machine was booted.
>=20
> Create a debugfs interface to make easier to test the API without real
> resets.
>=20
> Signed-off-by: Andr=C3=A9 Almeida <andrealmeid@igalia.com>
> ---
>  drivers/gpu/drm/drm_debugfs.c |  2 ++
>  drivers/gpu/drm/drm_ioctl.c   | 58 +++++++++++++++++++++++++++++++++++
>  include/drm/drm_device.h      |  3 ++
>  include/drm/drm_drv.h         |  3 ++
>  include/uapi/drm/drm.h        | 21 +++++++++++++
>  include/uapi/drm/drm_mode.h   | 15 +++++++++
>  6 files changed, 102 insertions(+)

...

> diff --git a/include/uapi/drm/drm.h b/include/uapi/drm/drm.h
> index a87bbbbca2d4..a84559aa0d77 100644
> --- a/include/uapi/drm/drm.h
> +++ b/include/uapi/drm/drm.h
> @@ -1169,6 +1169,27 @@ extern "C" {
>   */
>  #define DRM_IOCTL_MODE_GETFB2		DRM_IOWR(0xCE, struct drm_mode_fb_cmd2)
> =20
> +/**
> + * DRM_IOCTL_GET_RESET - Get information about device resets
> + *
> + * This operation requests from the device information about resets. It =
should
> + * consider only resets that happens after the context is created, there=
fore,
> + * the counter should be zero during context creation.
> + *
> + * dev_reset_count tells how many resets have happened on this device, a=
nd
> + * ctx_reset_count tells how many of such resets were caused by this con=
text.
> + *
> + * Flags can be used to tell if a reset is in progress, and userspace sh=
ould
> + * wait until it's not in progress anymore to be able to create a new co=
ntext;
> + * and to tell if the VRAM is considered lost. There's no safe way to cl=
ean this
> + * flag so if a context see this flag set, it should be like that until =
the end
> + * of the context.

Is "this flag" the VRAM_LOST? Or any flag?

Does this mean that not all resets are fatal to the context? Is there
any kind of reset that should not be fatal to a context? All the
rendering APIs seem to assume that any reset is fatal and the context
must be destroyed.

> + */
> +#define DRM_IOCTL_GET_RESET		DRM_IOWR(0xCF, struct drm_get_reset)
> +
> +#define DRM_RESET_IN_PROGRESS	0x1
> +#define DRM_RESET_VRAM_LOST	0x2

Ok, so the dmabuf lost is being communicated here, but how would a
userspace process know on which device a dmabuf resides on?

Let's assume process A uses device 1 to draw, exports a dmabuf, sends
it to process B which imports it to device 2. Device 1 resets and loses
VRAM contents. How would process B notice that the dmabuf is lost when
it never touches device 1 itself?

> +
>  /*
>   * Device specific ioctls should only be in their respective headers
>   * The device specific ioctl range is from 0x40 to 0x9f.
> diff --git a/include/uapi/drm/drm_mode.h b/include/uapi/drm/drm_mode.h
> index 43691058d28f..c3257bd1af9c 100644
> --- a/include/uapi/drm/drm_mode.h
> +++ b/include/uapi/drm/drm_mode.h
> @@ -1308,6 +1308,21 @@ struct drm_mode_rect {
>  	__s32 y2;
>  };
> =20
> +/**
> + * struct drm_get_reset - Get information about a DRM device resets
> + * @ctx_id: the context id to be queried about resets
> + * @flags: flags
> + * @dev_reset_count: global counter of resets for a given DRM device
> + * @ctx_reset_count: of all the resets counted by this device, how many =
were
> + * caused by this context.
> + */
> +struct drm_get_reset {
> +	__u32 ctx_id;
> +	__u32 flags;
> +	__u64 dev_reset_count;
> +	__u64 ctx_reset_count;
> +};
> +
>  #if defined(__cplusplus)
>  }
>  #endif

Thanks,
pq

--Sig_/ATv9R6N/IyatZ_qIv8rdPJF
Content-Type: application/pgp-signature
Content-Description: OpenPGP digital signature

-----BEGIN PGP SIGNATURE-----

iQIzBAEBCAAdFiEEJQjwWQChkWOYOIONI1/ltBGqqqcFAmSSsDsACgkQI1/ltBGq
qqfn+Q//SNCwyNu1uoLUvuP9SdsIToY76Ebck8cgr/wxhOOv2NFDulfmpaMKW9X2
Skf4kC+BJNM/myZhtmQ3iOJz7AdefkFAcScATWdGpjbs4pEqJxhNeNoV0UpMl3mt
yHcqFXLtPI4ofsrwGNeQeuVVUPRVWnO3RgN4I3j5egmBj4QJtW57atw60PxNBAmj
qakSMLdfhW7K148tOX5AMbxDJ1wnQctGAEV79TBzH7N9iacRR7AwpFyhho7T71ho
ll8NnWBEdabmPqpV29ewuY+2pqXepdxRdIXaoHA5WLffk8wB2muwPsyRdB3CmQh1
NcfUOBc6/pOlTxCwRgriHd7Scff76gGnJhdis06AHgfVIofRiPLbLSr518elLioO
a4B5LYPLbZY/p328pD7aW9bJTodQ514RL0YhI7D1z01KQR/FZ2/h4WdOQHSnm6Rg
UDzUGEoqTNseyFNwpwbJneY2jMnS3HpgWf7i5gmOTLCwize8g/8jNU+HL5kz/u5+
tarXS+WB0eQy5mmJFdgQ+om8XJpFnfAJqc4jU3fU3qsKro6l72BSek4YvSQNoJdc
ajVaQOgNqK2+V/Y5/6tH+OhoADRfvJ/YrUupVdydNr7Kc+ff+kwRDOH0IHOEwMK6
eafZ1GWhCEmoiqzXRFvNkcaLegQSoFECKsZfZ63Vnz8/RJTz7q0=
=DOkA
-----END PGP SIGNATURE-----

--Sig_/ATv9R6N/IyatZ_qIv8rdPJF--