feat(pci): MSI-X support

cloud-hypervisor only supports MSI-X interrupts for PCI devices, so
support for MSI-X is needed to support running on it. Additionally,
MSI-X can allow us to set separate interrupt handlers for the
configuration change interrupts and queue updates (even per-queue
handlers once we have multiple queues) in the future.

MSI-X is not working correctly or at all on all platforms, so it is
exposed as an optional feature.

Co-authored-by: Martin Kröning <mkroening@posteo.net>

Author: cagatay-y

.github/workflows/ci.yml

@@ -42,28 +42,28 @@ jobs:
       - run: rustup component add clippy
       - name: cargo hack clippy (x86_64)
         run: |
-          cargo hack clippy --package hermit-kernel --each-feature --no-dev-deps --target x86_64-unknown-none --exclude-features dhcpv4,dns,gem-net,net,rtl8139,virtio-net
-          cargo hack clippy --package hermit-kernel --each-feature --no-dev-deps --target x86_64-unknown-none --exclude-features dhcpv4,dns,gem-net,net,rtl8139,virtio-net --features pci
-          cargo hack clippy --package hermit-kernel --each-feature --no-dev-deps --target x86_64-unknown-none --exclude-features gem-net,rtl8139 --features tcp,virtio-net
+          cargo hack clippy --package hermit-kernel --each-feature --no-dev-deps --target x86_64-unknown-none --exclude-features dhcpv4,dns,gem-net,net,rtl8139,virtio-net,msix
+          cargo hack clippy --package hermit-kernel --each-feature --no-dev-deps --target x86_64-unknown-none --exclude-features dhcpv4,dns,gem-net,net,rtl8139,virtio-net,msix --features pci
+          cargo hack clippy --package hermit-kernel --each-feature --no-dev-deps --target x86_64-unknown-none --exclude-features gem-net,rtl8139,msix --features tcp,virtio-net
           cargo hack clippy --package hermit-kernel --each-feature --no-dev-deps --target x86_64-unknown-none --exclude-features gem-net,rtl8139 --features pci,tcp,virtio-net
-          cargo hack clippy --package hermit-kernel --each-feature --no-dev-deps --target x86_64-unknown-none --exclude-features gem-net,virtio-net --features tcp,rtl8139
-          cargo hack clippy --package hermit-kernel --each-feature --no-dev-deps --target x86_64-unknown-none --exclude-features gem-net,virtio-net --features pci,tcp,rtl8139
+          cargo hack clippy --package hermit-kernel --each-feature --no-dev-deps --target x86_64-unknown-none --exclude-features gem-net,virtio-net,msix --features tcp,rtl8139
+          cargo hack clippy --package hermit-kernel --each-feature --no-dev-deps --target x86_64-unknown-none --exclude-features gem-net,virtio-net,msix --features pci,tcp,rtl8139
       - name: cargo hack clippy (aarch64)
         run: |
-          cargo hack clippy --package hermit-kernel --each-feature --no-dev-deps --target aarch64-unknown-none-softfloat --exclude-features dhcpv4,dns,gem-net,net,rtl8139,virtio-net
-          cargo hack clippy --package hermit-kernel --each-feature --no-dev-deps --target aarch64-unknown-none-softfloat --exclude-features dhcpv4,dns,gem-net,net,rtl8139,virtio-net --features pci
-          cargo hack clippy --package hermit-kernel --each-feature --no-dev-deps --target aarch64-unknown-none-softfloat --exclude-features gem-net,rtl8139 --features tcp,virtio-net
-          cargo hack clippy --package hermit-kernel --each-feature --no-dev-deps --target aarch64-unknown-none-softfloat --exclude-features gem-net,rtl8139 --features pci,tcp,virtio-net
-          cargo hack clippy --package hermit-kernel --each-feature --no-dev-deps --target aarch64-unknown-none-softfloat --exclude-features gem-net,virtio-net --features tcp,rtl8139
-          cargo hack clippy --package hermit-kernel --each-feature --no-dev-deps --target aarch64-unknown-none-softfloat --exclude-features gem-net,virtio-net --features pci,tcp,rtl8139
+          cargo hack clippy --package hermit-kernel --each-feature --no-dev-deps --target aarch64-unknown-none-softfloat --exclude-features dhcpv4,dns,gem-net,net,rtl8139,virtio-net,msix
+          cargo hack clippy --package hermit-kernel --each-feature --no-dev-deps --target aarch64-unknown-none-softfloat --exclude-features dhcpv4,dns,gem-net,net,rtl8139,virtio-net,msix --features pci
+          cargo hack clippy --package hermit-kernel --each-feature --no-dev-deps --target aarch64-unknown-none-softfloat --exclude-features gem-net,rtl8139,msix --features tcp,virtio-net
+          cargo hack clippy --package hermit-kernel --each-feature --no-dev-deps --target aarch64-unknown-none-softfloat --exclude-features gem-net,rtl8139,msix --features pci,tcp,virtio-net
+          cargo hack clippy --package hermit-kernel --each-feature --no-dev-deps --target aarch64-unknown-none-softfloat --exclude-features gem-net,virtio-net,msix --features tcp,rtl8139
+          cargo hack clippy --package hermit-kernel --each-feature --no-dev-deps --target aarch64-unknown-none-softfloat --exclude-features gem-net,virtio-net,msix --features pci,tcp,rtl8139
       - name: cargo hack clippy (riscv64)
         run: |
-          cargo hack clippy --package hermit-kernel --each-feature --no-dev-deps --target riscv64gc-unknown-none-elf --exclude-features dhcpv4,dns,gem-net,net,rtl8139,virtio-net
-          cargo hack clippy --package hermit-kernel --each-feature --no-dev-deps --target riscv64gc-unknown-none-elf --exclude-features dhcpv4,dns,gem-net,net,rtl8139,virtio-net --features pci
-          cargo hack clippy --package hermit-kernel --each-feature --no-dev-deps --target riscv64gc-unknown-none-elf --exclude-features gem-net,rtl8139 --features tcp,virtio-net
-          cargo hack clippy --package hermit-kernel --each-feature --no-dev-deps --target riscv64gc-unknown-none-elf --exclude-features gem-net,rtl8139 --features pci,tcp,virtio-net
-          cargo hack clippy --package hermit-kernel --each-feature --no-dev-deps --target riscv64gc-unknown-none-elf --exclude-features rtl8139,virtio-net --features tcp,gem-net
-          cargo hack clippy --package hermit-kernel --each-feature --no-dev-deps --target riscv64gc-unknown-none-elf --exclude-features rtl8139,virtio-net --features pci,tcp,gem-net
+          cargo hack clippy --package hermit-kernel --each-feature --no-dev-deps --target riscv64gc-unknown-none-elf --exclude-features dhcpv4,dns,gem-net,net,rtl8139,virtio-net,msix
+          cargo hack clippy --package hermit-kernel --each-feature --no-dev-deps --target riscv64gc-unknown-none-elf --exclude-features dhcpv4,dns,gem-net,net,rtl8139,virtio-net,msix --features pci
+          cargo hack clippy --package hermit-kernel --each-feature --no-dev-deps --target riscv64gc-unknown-none-elf --exclude-features gem-net,rtl8139,msix --features tcp,virtio-net
+          cargo hack clippy --package hermit-kernel --each-feature --no-dev-deps --target riscv64gc-unknown-none-elf --exclude-features gem-net,rtl8139,msix --features pci,tcp,virtio-net
+          cargo hack clippy --package hermit-kernel --each-feature --no-dev-deps --target riscv64gc-unknown-none-elf --exclude-features rtl8139,virtio-net,msix --features tcp,gem-net
+          cargo hack clippy --package hermit-kernel --each-feature --no-dev-deps --target riscv64gc-unknown-none-elf --exclude-features rtl8139,virtio-net,msix --features pci,tcp,gem-net
 
   format:
     name: Format

Cargo.toml

@@ -118,6 +118,12 @@ pci = ["virtio?/pci"]
 ## [PCI ID]: https://pci-ids.ucw.cz/
 pci-ids = ["dep:pci-ids"]
 
+## Causes the drivers to use _MSI-X (Message Signaled Interrupt)_ when
+## the PCI device and the driver (currently only virtio-net) supports it. 
+## It is only supported on x86_64 and is known to not work with all virtual
+## devices.
+msix = ["volatile/derive"]
+
 ## Enables semihosting support.
 ##
 ## Semihosting allows communicating with the host for

src/drivers/net/virtio/mmio.rs

@@ -39,7 +39,7 @@ impl VirtioNetDriver<Uninit> {
 			notif_cfg,
 			inner: Uninit,
 			num_vqs: 0,
-			irq,
+			irq: Some(irq),
 			checksums: ChecksumCapabilities::default(),
 		})
 	}

src/drivers/net/virtio/mod.rs

@@ -33,6 +33,8 @@ use self::error::VirtioNetError;
 use crate::config::VIRTIO_MAX_QUEUE_SIZE;
 use crate::drivers::net::virtio::constants::BUFF_PER_PACKET;
 use crate::drivers::net::{NetworkDriver, mtu};
+#[cfg(feature = "msix")]
+use crate::drivers::pci::MsixTableEntry;
 use crate::drivers::virtio::ControlRegisters;
 #[cfg(not(feature = "pci"))]
 use crate::drivers::virtio::transport::mmio::{ComCfg, IsrStatus, NotifCfg};
@@ -241,11 +243,13 @@ pub(crate) struct VirtioNetDriver<T = Init> {
 	pub(super) com_cfg: ComCfg,
 	pub(super) isr_stat: IsrStatus,
 	pub(super) notif_cfg: NotifCfg,
+	#[cfg(feature = "msix")]
+	pub(super) msix_table: Option<VolatileRef<'static, [MsixTableEntry]>>,
 
 	pub(super) inner: T,
 
 	pub(super) num_vqs: u16,
-	pub(super) irq: InterruptLine,
+	pub(super) irq: Option<InterruptLine>,
 	pub(super) checksums: ChecksumCapabilities,
 }
 
@@ -485,7 +489,7 @@ impl smoltcp::phy::Device for VirtioNetDriver {
 
 impl Driver for VirtioNetDriver<Init> {
 	fn get_interrupt_number(&self) -> InterruptLine {
-		self.irq
+		self.irq.unwrap()
 	}
 
 	fn get_name(&self) -> &'static str {
@@ -741,11 +745,34 @@ impl VirtioNetDriver<Uninit> {
 		}
 		debug!("{:?}", self.checksums);
 
+		#[cfg(feature = "msix")]
+		if let Some(msix_table) = self.msix_table.as_mut() {
+			warn!(
+				"Setting up message signaled interrupts. MSI-X is known to not work on all platforms (e.g. QEMU with TAP)."
+			);
+			// Chosen arbitatrily. Ideally does not clash with another interrupt line.
+			const MSIX_VECTOR: u8 = 112;
+			let msix_entry = unsafe {
+				msix_table
+					.as_mut_ptr()
+					.map(|table| table.get_unchecked_mut(0))
+			};
+			MsixTableEntry::configure(msix_entry, MSIX_VECTOR);
+			self.com_cfg.select_vq(0).unwrap().set_msix_table_index(0);
+			self.irq = Some(MSIX_VECTOR);
+		};
+
+		if self.irq.is_none() {
+			warn!("No interrupt methods found for virtio-net.");
+		}
+
 		Ok(VirtioNetDriver {
 			dev_cfg: self.dev_cfg,
 			com_cfg: self.com_cfg,
 			isr_stat: self.isr_stat,
 			notif_cfg: self.notif_cfg,
+			#[cfg(feature = "msix")]
+			msix_table: self.msix_table,
 			inner,
 			num_vqs: self.num_vqs,
 			irq: self.irq,

src/drivers/net/virtio/pci.rs

@@ -36,6 +36,8 @@ impl VirtioNetDriver<Uninit> {
 			notif_cfg,
 			isr_cfg,
 			dev_cfg_list,
+			#[cfg(feature = "msix")]
+			msix_table,
 			..
 		} = caps_coll;
 
@@ -44,14 +46,18 @@ impl VirtioNetDriver<Uninit> {
 			return Err(error::VirtioNetError::NoDevCfg(device_id));
 		};
 
+		let irq = device.get_irq();
+
 		Ok(VirtioNetDriver {
 			dev_cfg,
 			com_cfg,
 			isr_stat: isr_cfg,
 			notif_cfg,
+			#[cfg(feature = "msix")]
+			msix_table,
 			inner: Uninit,
 			num_vqs: 0,
-			irq: device.get_irq().unwrap(),
+			irq,
 			checksums: ChecksumCapabilities::default(),
 		})
 	}

src/drivers/pci.rs

@@ -537,6 +537,49 @@ pub(crate) fn init() {
 	});
 }
 
+/// MSI-X Table entry.  
+#[cfg(feature = "msix")]
+#[repr(C)]
+#[derive(volatile::VolatileFieldAccess)]
+pub(crate) struct MsixTableEntry {
+	/// Message Address
+	message_address: u32,
+
+	/// Message Upper Address
+	message_upper_address: u32,
+
+	/// Message Data
+	message_data: u32,
+
+	/// Vector Control
+	vector_control: u32,
+}
+
+#[cfg(feature = "msix")]
+impl MsixTableEntry {
+	#[cfg(target_arch = "x86_64")]
+	pub fn configure(msix_entry: volatile::VolatilePtr<'_, Self>, vector: u8) {
+		use MsixTableEntryVolatileFieldAccess;
+		use bit_field::BitField;
+
+		// Mask the entry because "[s]oftware must not modify the Address, Data, or Steering Tag fields
+		// of an entry while it is unmasked." (PCIe spec. 6.1.4.2)
+		msix_entry
+			.vector_control()
+			.update(|mut control| *control.set_bit(0, true));
+
+		msix_entry
+			.message_address()
+			.update(|mut addr_low| *addr_low.set_bits(20..32, 0xfee));
+		msix_entry
+			.message_data()
+			.update(|mut data| *data.set_bits(0..8, u32::from(vector) + 32));
+		msix_entry
+			.vector_control()
+			.update(|mut control| *control.set_bit(0, false));
+	}
+}
+
 /// A module containing PCI specific errors
 ///
 /// Errors include...