On Thu Dec 18, 2025 at 2:39 AM CET, Timur Tabi wrote:
> From: Alexandre Courbot <[email protected]>
>
> `LogBuffer` is the entity we ultimately want to dump through debugfs.
> Provide a simple implementation of `BinaryWriter` for it, albeit it
> might not cut the safety requirements.
>
> Signed-off-by: Alexandre Courbot <[email protected]>
> Signed-off-by: Timur Tabi <[email protected]>
> ---
> drivers/gpu/nova-core/gsp.rs | 24 ++++++++++++++++++++++++
> 1 file changed, 24 insertions(+)
>
> diff --git a/drivers/gpu/nova-core/gsp.rs b/drivers/gpu/nova-core/gsp.rs
> index fb6f74797178..860674dac31e 100644
> --- a/drivers/gpu/nova-core/gsp.rs
> +++ b/drivers/gpu/nova-core/gsp.rs
> @@ -3,6 +3,7 @@
> mod boot;
>
> use kernel::{
> + debugfs,
> device,
> dma::{
> CoherentAllocation,
> @@ -117,6 +118,29 @@ pub(crate) struct Gsp {
> rmargs: CoherentAllocation<GspArgumentsCached>,
> }
>
> +impl debugfs::BinaryWriter for LogBuffer {
> + fn write_to_slice(
> + &self,
> + writer: &mut kernel::uaccess::UserSliceWriter,
> + offset: &mut kernel::fs::file::Offset,
> + ) -> Result<usize> {
> + // SAFETY: This is a debug log buffer. GSP may write concurrently,
> so the
> + // snapshot may contain partially-written entries. This is
> acceptable for
> + // debugging purposes - users should be aware logs may be slightly
> garbled
> + // if read while GSP is actively logging.
> + let slice = unsafe { self.0.as_slice(0, self.0.count()) }?;
Unfortunately, it's still undefined behavior to create a slice when the backing
buffer can change unexpectedly.
You can use UserSliceWriter::write() instead or add an unsafe method to
UserSliceWriter that takes a raw pointer, length and offset.
Given the context of a debug log buffer, I suggest the former.
> + writer.write_slice_file(slice, offset)
> + }
> +}
> +
> +// SAFETY: `LogBuffer` only provides shared access to the underlying
> `CoherentAllocation`.
> +// GSP may write to the buffer concurrently regardless of CPU access, so
> concurrent reads
> +// from multiple CPU threads do not introduce any additional races beyond
> what already
> +// exists with the device. Reads may observe partially-written log entries,
> which is
> +// acceptable for debug logging purposes.
> +unsafe impl Sync for LogBuffer {}
> +
> impl Gsp {
> // Creates an in-place initializer for a `Gsp` manager for `pdev`.
> pub(crate) fn new(pdev: &pci::Device<device::Bound>) -> Result<impl
> PinInit<Self, Error>> {
> --
> 2.52.0
