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Message-ID: <CAO-hwJKnnVkJPG6wtLJ6t7ojv5=vS0NGt14un6+nRmxzj+xifw@mail.gmail.com> Date: Tue, 29 Mar 2022 15:53:41 +0200 From: Benjamin Tissoires <benjamin.tissoires@...hat.com> To: Andrii Nakryiko <andrii.nakryiko@...il.com> Cc: Alexei Starovoitov <alexei.starovoitov@...il.com>, Greg KH <gregkh@...uxfoundation.org>, Jiri Kosina <jikos@...nel.org>, Alexei Starovoitov <ast@...nel.org>, Daniel Borkmann <daniel@...earbox.net>, Andrii Nakryiko <andrii@...nel.org>, Martin KaFai Lau <kafai@...com>, Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>, John Fastabend <john.fastabend@...il.com>, KP Singh <kpsingh@...nel.org>, Shuah Khan <shuah@...nel.org>, Dave Marchevsky <davemarchevsky@...com>, Joe Stringer <joe@...ium.io>, Jonathan Corbet <corbet@....net>, Tero Kristo <tero.kristo@...ux.intel.com>, LKML <linux-kernel@...r.kernel.org>, "open list:HID CORE LAYER" <linux-input@...r.kernel.org>, Network Development <netdev@...r.kernel.org>, bpf <bpf@...r.kernel.org>, "open list:KERNEL SELFTEST FRAMEWORK" <linux-kselftest@...r.kernel.org>, "open list:DOCUMENTATION" <linux-doc@...r.kernel.org> Subject: Re: [PATCH bpf-next v3 06/17] HID: allow to change the report descriptor from an eBPF program On Mon, Mar 28, 2022 at 11:35 PM Andrii Nakryiko <andrii.nakryiko@...il.com> wrote: > > On Sun, Mar 27, 2022 at 11:57 PM Benjamin Tissoires > <benjamin.tissoires@...hat.com> wrote: > > > > On Fri, Mar 25, 2022 at 6:00 PM Andrii Nakryiko > > <andrii.nakryiko@...il.com> wrote: > > > > > > On Wed, Mar 23, 2022 at 9:08 AM Benjamin Tissoires > > > <benjamin.tissoires@...hat.com> wrote: > > > > > > > > Hi Alexei, > > > > > > > > On Tue, Mar 22, 2022 at 11:51 PM Alexei Starovoitov > > > > <alexei.starovoitov@...il.com> wrote: > > > > > > > > > > On Fri, Mar 18, 2022 at 9:16 AM Benjamin Tissoires > > > > > <benjamin.tissoires@...hat.com> wrote: > > > > > > > > > > > > +u8 *hid_bpf_report_fixup(struct hid_device *hdev, u8 *rdesc, unsigned int *size) > > > > > > +{ > > > > > > + int ret; > > > > > > + struct hid_bpf_ctx_kern ctx = { > > > > > > + .type = HID_BPF_RDESC_FIXUP, > > > > > > + .hdev = hdev, > > > > > > + .size = *size, > > > > > > + }; > > > > > > + > > > > > > + if (bpf_hid_link_empty(&hdev->bpf, BPF_HID_ATTACH_RDESC_FIXUP)) > > > > > > + goto ignore_bpf; > > > > > > + > > > > > > + ctx.data = kmemdup(rdesc, HID_MAX_DESCRIPTOR_SIZE, GFP_KERNEL); > > > > > > + if (!ctx.data) > > > > > > + goto ignore_bpf; > > > > > > + > > > > > > + ctx.allocated_size = HID_MAX_DESCRIPTOR_SIZE; > > > > > > + > > > > > > + ret = hid_bpf_run_progs(hdev, &ctx); > > > > > > + if (ret) > > > > > > + goto ignore_bpf; > > > > > > + > > > > > > + if (ctx.size > ctx.allocated_size) > > > > > > + goto ignore_bpf; > > > > > > + > > > > > > + *size = ctx.size; > > > > > > + > > > > > > + if (*size) { > > > > > > + rdesc = krealloc(ctx.data, *size, GFP_KERNEL); > > > > > > + } else { > > > > > > + rdesc = NULL; > > > > > > + kfree(ctx.data); > > > > > > + } > > > > > > + > > > > > > + return rdesc; > > > > > > + > > > > > > + ignore_bpf: > > > > > > + kfree(ctx.data); > > > > > > + return kmemdup(rdesc, *size, GFP_KERNEL); > > > > > > +} > > > > > > + > > > > > > int __init hid_bpf_module_init(void) > > > > > > { > > > > > > struct bpf_hid_hooks hooks = { > > > > > > .hdev_from_fd = hid_bpf_fd_to_hdev, > > > > > > .pre_link_attach = hid_bpf_pre_link_attach, > > > > > > + .post_link_attach = hid_bpf_post_link_attach, > > > > > > .array_detach = hid_bpf_array_detach, > > > > > > }; > > > > > > > > > > > > diff --git a/drivers/hid/hid-core.c b/drivers/hid/hid-core.c > > > > > > index 937fab7eb9c6..3182c39db006 100644 > > > > > > --- a/drivers/hid/hid-core.c > > > > > > +++ b/drivers/hid/hid-core.c > > > > > > @@ -1213,7 +1213,8 @@ int hid_open_report(struct hid_device *device) > > > > > > return -ENODEV; > > > > > > size = device->dev_rsize; > > > > > > > > > > > > - buf = kmemdup(start, size, GFP_KERNEL); > > > > > > + /* hid_bpf_report_fixup() ensures we work on a copy of rdesc */ > > > > > > + buf = hid_bpf_report_fixup(device, start, &size); > > > > > > > > > > Looking at this patch and the majority of other patches... > > > > > the code is doing a lot of work to connect HID side with bpf. > > > > > At the same time the evolution of the patch series suggests > > > > > that these hook points are not quite stable. More hooks and > > > > > helpers are being added. > > > > > It tells us that it's way too early to introduce a stable > > > > > interface between HID and bpf. > > > > > > > > I understand that you might be under the impression that the interface > > > > is changing a lot, but this is mostly due to my poor knowledge of all > > > > the arcanes of eBPF. > > > > The overall way HID-BPF works is to work on a single array, and we > > > > should pretty much be sorted out. There are a couple of helpers to be > > > > able to communicate with the device, but the API has been stable in > > > > the kernel for those for quite some time now. > > > > > > > > The variations in the hooks is mostly because I don't know what is the > > > > best representation we can use in eBPF for those, and the review > > > > process is changing that. > > > > > > I think such a big feature as this one, especially that most BPF folks > > > are (probably) not familiar with the HID subsystem in the kernel, > > > would benefit from a bit of live discussion during BPF office hours. > > > Do you think you can give a short overview of what you are trying to > > > achieve with some background context on HID specifics at one of the > > > next BPF office hours? We have a meeting scheduled every week on > > > Thursday, 9am Pacific time. But people need to put their topic onto > > > the agenda, otherwise the meeting is cancelled. See [0] for > > > spreadsheet and links to Zoom meeting, agenda, etc. > > > > This sounds like a good idea. I just added my topic on the agenda and > > will prepare some slides. > > > > Great! Unfortunately I personally have a conflict this week and won't > be able to attend, so I'll have to catch up somehow through word of > mouth :( Next week's BPF office hours would be best, but I don't want > to delay discussions just because of me. OK. FWIW, I'll have slides publicly available once I'll do a final roundup on them. Hopefully that will give you enough context on HID to understand the problem. If there are too many conflicts we can surely delay by a week, but I would rather have the discussion happening sooner :/ Cheers, Benjamin > > > > > > > > [0] https://docs.google.com/spreadsheets/d/1LfrDXZ9-fdhvPEp_LHkxAMYyxxpwBXjywWa0AejEveU > > > > > > [...] > > > > > >
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