Re: [POC 2/6] rust: Introduce interrupt module

[Lyude Paul <lyude@redhat.com>]

Whoops - realized I should clarify. We should definitely keep the actual
InterruptDisabled token, but we want to get rid of the actual functions for
manually disabling interrupts.

On Thu, 2024-10-31 at 16:45 -0400, Lyude Paul wrote:
> On Thu, 2024-10-17 at 22:51 -0700, Boqun Feng wrote:
> > From: Lyude Paul <lyude@redhat.com>
> > 
> > This introduces a module for dealing with interrupt-disabled contexts,
> > including the ability to enable and disable interrupts along with the
> > ability to annotate functions as expecting that IRQs are already
> > disabled on the local CPU.
> > 
> > [Boqun: This is based on Lyude's work on interrupt disable abstraction,
> > I port to the new local_interrupt_disable() mechanism to make it work
> > as a guard type. I cannot even take the credit of this design, since
> > Lyude also brought up the same idea in zulip. Anyway, this is only for
> > POC purpose, and of course all bugs are mine]
> 
> TBH sine as tglx pointed out we don't really want to have direct interrupt
> controls, maybe it would be better to leave this part of the series out for
> now? We could add it back someday if needed, but I think for the time being
> it's probably better to just encourage people to use the primitives that we
> provide rather than trying to control interrupts directly. Especially w/r/t
> the PREEMPT_RT considerations.
> 
> > 
> > Co-Developed-by: Lyude Paul <lyude@redhat.com>
> > Signed-off-by: Lyude Paul <lyude@redhat.com>
> > Signed-off-by: Boqun Feng <boqun.feng@gmail.com>
> > ---
> >  rust/helpers/helpers.c   |  1 +
> >  rust/helpers/interrupt.c | 18 +++++++++++
> >  rust/kernel/interrupt.rs | 64 ++++++++++++++++++++++++++++++++++++++++
> >  rust/kernel/lib.rs       |  1 +
> >  4 files changed, 84 insertions(+)
> >  create mode 100644 rust/helpers/interrupt.c
> >  create mode 100644 rust/kernel/interrupt.rs
> > 
> > diff --git a/rust/helpers/helpers.c b/rust/helpers/helpers.c
> > index 30f40149f3a9..f6e5b33eaff8 100644
> > --- a/rust/helpers/helpers.c
> > +++ b/rust/helpers/helpers.c
> > @@ -12,6 +12,7 @@
> >  #include "build_assert.c"
> >  #include "build_bug.c"
> >  #include "err.c"
> > +#include "interrupt.c"
> >  #include "kunit.c"
> >  #include "mutex.c"
> >  #include "page.c"
> > diff --git a/rust/helpers/interrupt.c b/rust/helpers/interrupt.c
> > new file mode 100644
> > index 000000000000..e58da42916da
> > --- /dev/null
> > +++ b/rust/helpers/interrupt.c
> > @@ -0,0 +1,18 @@
> > +// SPDX-License-Identifier: GPL-2.0
> > +
> > +#include <linux/irqflags.h>
> > +
> > +void rust_helper_local_interrupt_disable(void)
> > +{
> > +	local_interrupt_disable();
> > +}
> > +
> > +void rust_helper_local_interrupt_enable(void)
> > +{
> > +	local_interrupt_enable();
> > +}
> > +
> > +bool rust_helper_irqs_disabled(void)
> > +{
> > +	return irqs_disabled();
> > +}
> > diff --git a/rust/kernel/interrupt.rs b/rust/kernel/interrupt.rs
> > new file mode 100644
> > index 000000000000..fe5a36877538
> > --- /dev/null
> > +++ b/rust/kernel/interrupt.rs
> > @@ -0,0 +1,64 @@
> > +// SPDX-License-Identifier: GPL-2.0
> > +
> > +//! Interrupt controls
> > +//!
> > +//! This module allows Rust code to control processor interrupts. [`with_interrupt_disabled()`] may be
> > +//! used for nested disables of interrupts, whereas [`InterruptDisabled`] can be used for annotating code
> > +//! that requires interrupts to be disabled.
> > +
> > +use bindings;
> > +use core::marker::*;
> > +
> > +/// XXX: Temporarily definition for NotThreadSafe
> > +pub type NotThreadSafe = PhantomData<*mut ()>;
> > +
> > +/// XXX: Temporarily const for NotThreadSafe
> > +#[allow(non_upper_case_globals)]
> > +pub const NotThreadSafe: NotThreadSafe = PhantomData;
> > +
> > +/// A guard that represent interrupt disable protection.
> > +///
> > +/// [`InterruptDisabled`] is a guard type that represent interrupts have been disabled. Certain
> > +/// functions take an immutable reference of [`InterruptDisabled`] in order to require that they may
> > +/// only be run in interrupt-disabled contexts.
> > +///
> > +/// This is a marker type; it has no size, and is simply used as a compile-time guarantee that
> > +/// interrupts are disabled where required.
> > +///
> > +/// This token can be created by [`with_interrupt_disabled`]. See [`with_interrupt_disabled`] for examples and
> > +/// further information.
> > +///
> > +/// # Invariants
> > +///
> > +/// Interrupts are disabled with `local_interrupt_disable()` when an object of this type exists.
> > +pub struct InterruptDisabled(NotThreadSafe);
> > +
> > +/// Disable interrupts.
> > +pub fn interrupt_disable() -> InterruptDisabled {
> > +    // SAFETY: It's always safe to call `local_interrupt_disable()`.
> > +    unsafe { bindings::local_interrupt_disable() };
> > +
> > +    InterruptDisabled(NotThreadSafe)
> > +}
> > +
> > +impl Drop for InterruptDisabled {
> > +    fn drop(&mut self) {
> > +        // SAFETY: Per type invariants, a `local_interrupt_disable()` must be called to create this
> > +        // object, hence call the corresponding `local_interrupt_enable()` is safe.
> > +        unsafe { bindings::local_interrupt_enable() };
> > +    }
> > +}
> > +
> > +impl InterruptDisabled {
> > +    const ASSUME_INTERRUPT_DISABLED: &'static InterruptDisabled = &InterruptDisabled(NotThreadSafe);
> > +
> > +    /// Assume that interrupts are disabled.
> > +    ///
> > +    /// # Safety
> > +    ///
> > +    /// For the whole life `'a`, interrupts must be considered disabled, for example an interrupt
> > +    /// handler.
> > +    pub unsafe fn assume_interrupt_disabled<'a>() -> &'a InterruptDisabled {
> > +        Self::ASSUME_INTERRUPT_DISABLED
> > +    }
> > +}
> > diff --git a/rust/kernel/lib.rs b/rust/kernel/lib.rs
> > index b5f4b3ce6b48..56ff464b7905 100644
> > --- a/rust/kernel/lib.rs
> > +++ b/rust/kernel/lib.rs
> > @@ -35,6 +35,7 @@
> >  #[cfg(CONFIG_RUST_FW_LOADER_ABSTRACTIONS)]
> >  pub mod firmware;
> >  pub mod init;
> > +pub mod interrupt;
> >  pub mod ioctl;
> >  #[cfg(CONFIG_KUNIT)]
> >  pub mod kunit;
> 

-- 
Cheers,
 Lyude Paul (she/her)
 Software Engineer at Red Hat

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