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Date: Wed, 09 Sep 2026 22:13:09 +0200
Message-Id: <DLB26IJOGT28.6EW1J23QCYM3@kernel.org>
Subject: Re: [PATCH 15/16] gpu: nova-core: mm: Add BAR1 user interface
Cc: "Alexandre Courbot" <acourbot@nvidia.com>, "Alice Ryhl"
 <aliceryhl@google.com>, "John Hubbard" <jhubbard@nvidia.com>, "Alistair
 Popple" <apopple@nvidia.com>, "Timur Tabi" <ttabi@nvidia.com>,
 <nova-gpu@lists.linux.dev>, <dri-devel@lists.freedesktop.org>,
 <linux-kernel@vger.kernel.org>, "Joel Fernandes" <joelagnelf@nvidia.com>
To: "Eliot Courtney" <ecourtney@nvidia.com>
From: "Danilo Krummrich" <dakr@kernel.org>
References: <20260909-mmrebase-v1-0-8dd5d4225d2e@nvidia.com>
 <20260909-mmrebase-v1-15-8dd5d4225d2e@nvidia.com>
In-Reply-To: <20260909-mmrebase-v1-15-8dd5d4225d2e@nvidia.com>

On Wed Sep 9, 2026 at 5:59 AM CEST, Eliot Courtney wrote:
> +/// Access object for a mapped BAR1 region.
> +pub(crate) struct BarUserAccess<'gpu> {
> +    bar_user: Arc<BarUser<'gpu>>,

This shouldn't be an Arc, we can just borrow from BarUser.

> +    /// [`BarUserAccess::release`] [`Option::take`]s this; `Some` at
> +    /// drop time means `release()` was never called.
> +    mapped: Option<MappedRange>,

This Option, the panic in mapped() and the odd warning in drop() should go =
away
with using proper RAII types as suggested in a previous reply. I.e.
unmap_pages() doesn't need to call free_vfn() anymore, but MappedRange's dr=
op()
does it.

> +}
> +
> +impl BarUserAccess<'_> {
> +    /// Tear down the BAR1 mapping.
> +    pub(crate) fn release(mut self, mm: &mut GpuMm<'_>) -> Result {
> +        let mapped =3D self.mapped.take().ok_or(EINVAL)?;
> +        let mut vmm =3D self.bar_user.vmm.lock();
> +        vmm.unmap_pages(mm, mapped)?;
> +        Ok(())
> +    }
> +
> +    /// Returns the active mapping.
> +    fn mapped(&self) -> &MappedRange {
> +        // `mapped` is only `None` after `take()` in `release`; hence un=
wrap()
> +        // cannot panic here.
> +        self.mapped.as_ref().unwrap()
> +    }

[...]

> +impl Drop for BarUserAccess<'_> {
> +    fn drop(&mut self) {
> +        if self.mapped.is_some() {
> +            kernel::pr_warn!(
> +                "BarUserAccess dropped without calling release(). BarUse=
r address space will leak.\n"
> +            );
> +        }
> +        // The inner `MappedRange`'s own `MustUnmapGuard` will also fire=
,
> +        // identifying the leaked VA range.
> +    }
> +}