[PATCH RFC v6 11/26] nova-core: mm: Add MMU v2 page table types

[Joel Fernandes <joelagnelf@nvidia.com>]

Add page table entry and directory structures for MMU version 2
used by Turing/Ampere/Ada GPUs.

Signed-off-by: Joel Fernandes <joelagnelf@nvidia.com>
---
 drivers/gpu/nova-core/mm/pagetable/mod.rs  |   1 +
 drivers/gpu/nova-core/mm/pagetable/ver2.rs | 184 +++++++++++++++++++++
 2 files changed, 185 insertions(+)
 create mode 100644 drivers/gpu/nova-core/mm/pagetable/ver2.rs

diff --git a/drivers/gpu/nova-core/mm/pagetable/mod.rs b/drivers/gpu/nova-core/mm/pagetable/mod.rs
index bb3a37cc6ca0..787755e89a5b 100644
--- a/drivers/gpu/nova-core/mm/pagetable/mod.rs
+++ b/drivers/gpu/nova-core/mm/pagetable/mod.rs
@@ -7,6 +7,7 @@
 //! - Memory aperture types for PDEs and PTEs
 
 #![expect(dead_code)]
+pub(crate) mod ver2;
 
 use crate::gpu::Architecture;
 
diff --git a/drivers/gpu/nova-core/mm/pagetable/ver2.rs b/drivers/gpu/nova-core/mm/pagetable/ver2.rs
new file mode 100644
index 000000000000..d50c3e56d38e
--- /dev/null
+++ b/drivers/gpu/nova-core/mm/pagetable/ver2.rs
@@ -0,0 +1,184 @@
+// SPDX-License-Identifier: GPL-2.0
+
+//! MMU v2 page table types for Turing and Ampere GPUs.
+//!
+//! This module defines MMU version 2 specific types (Turing, Ampere and Ada GPUs).
+//!
+//! Bit field layouts derived from the NVIDIA OpenRM documentation:
+//! `open-gpu-kernel-modules/src/common/inc/swref/published/turing/tu102/dev_mmu.h`
+
+#![expect(dead_code)]
+
+use super::{
+    AperturePde,
+    AperturePte, //
+};
+use crate::mm::{
+    Pfn,
+    VramAddress, //
+};
+
+// Page Table Entry (PTE) for MMU v2 - 64-bit entry at level 4.
+bitfield! {
+    pub(crate) struct Pte(u64), "Page Table Entry for MMU v2" {
+        0:0     valid               as bool, "Entry is valid";
+        2:1     aperture            as u8 => AperturePte, "Memory aperture type";
+        3:3     volatile            as bool, "Volatile (bypass L2 cache)";
+        4:4     encrypted           as bool, "Encryption enabled (Confidential Computing)";
+        5:5     privilege           as bool, "Privileged access only";
+        6:6     read_only           as bool, "Write protection";
+        7:7     atomic_disable      as bool, "Atomic operations disabled";
+        53:8    frame_number_sys    as u64 => Pfn, "Frame number for system memory";
+        32:8    frame_number_vid    as u64 => Pfn, "Frame number for video memory";
+        35:33   peer_id             as u8, "Peer GPU ID for peer memory (0-7)";
+        53:36   comptagline         as u32, "Compression tag line bits";
+        63:56   kind                as u8, "Surface kind/format";
+    }
+}
+
+impl Pte {
+    /// Create a PTE from a `u64` value.
+    pub(crate) fn new(val: u64) -> Self {
+        Self(val)
+    }
+
+    /// Create a valid PTE for video memory.
+    pub(crate) fn new_vram(pfn: Pfn, writable: bool) -> Self {
+        Self::default()
+            .set_valid(true)
+            .set_aperture(AperturePte::VideoMemory)
+            .set_frame_number_vid(pfn)
+            .set_read_only(!writable)
+    }
+
+    /// Create an invalid PTE.
+    pub(crate) fn invalid() -> Self {
+        Self::default()
+    }
+
+    /// Get the frame number based on aperture type.
+    pub(crate) fn frame_number(&self) -> Pfn {
+        match self.aperture() {
+            AperturePte::VideoMemory => self.frame_number_vid(),
+            _ => self.frame_number_sys(),
+        }
+    }
+
+    /// Get the raw `u64` value.
+    pub(crate) fn raw_u64(&self) -> u64 {
+        self.0
+    }
+}
+
+// Page Directory Entry (PDE) for MMU v2 - 64-bit entry at levels 0-2.
+bitfield! {
+    pub(crate) struct Pde(u64), "Page Directory Entry for MMU v2" {
+        0:0     valid_inverted      as bool, "Valid bit (inverted logic)";
+        2:1     aperture            as u8 => AperturePde, "Memory aperture type";
+        3:3     volatile            as bool, "Volatile (bypass L2 cache)";
+        5:5     no_ats              as bool, "Disable Address Translation Services";
+        53:8    table_frame_sys     as u64 => Pfn, "Table frame number for system memory";
+        32:8    table_frame_vid     as u64 => Pfn, "Table frame number for video memory";
+        35:33   peer_id             as u8, "Peer GPU ID (0-7)";
+    }
+}
+
+impl Pde {
+    /// Create a PDE from a `u64` value.
+    pub(crate) fn new(val: u64) -> Self {
+        Self(val)
+    }
+
+    /// Create a valid PDE pointing to a page table in video memory.
+    pub(crate) fn new_vram(table_pfn: Pfn) -> Self {
+        Self::default()
+            .set_valid_inverted(false) // 0 = valid
+            .set_aperture(AperturePde::VideoMemory)
+            .set_table_frame_vid(table_pfn)
+    }
+
+    /// Create an invalid PDE.
+    pub(crate) fn invalid() -> Self {
+        Self::default()
+            .set_valid_inverted(true)
+            .set_aperture(AperturePde::Invalid)
+    }
+
+    /// Check if this PDE is valid.
+    pub(crate) fn is_valid(&self) -> bool {
+        !self.valid_inverted() && self.aperture() != AperturePde::Invalid
+    }
+
+    /// Get the table frame number based on aperture type.
+    pub(crate) fn table_frame(&self) -> Pfn {
+        match self.aperture() {
+            AperturePde::VideoMemory => self.table_frame_vid(),
+            _ => self.table_frame_sys(),
+        }
+    }
+
+    /// Get the VRAM address of the page table.
+    pub(crate) fn table_vram_address(&self) -> VramAddress {
+        debug_assert!(
+            self.aperture() == AperturePde::VideoMemory,
+            "table_vram_address called on non-VRAM PDE (aperture: {:?})",
+            self.aperture()
+        );
+        VramAddress::from(self.table_frame_vid())
+    }
+
+    /// Get the raw `u64` value of the PDE.
+    pub(crate) fn raw_u64(&self) -> u64 {
+        self.0
+    }
+}
+
+/// Dual PDE at Level 3 - 128-bit entry of Large/Small Page Table pointers.
+///
+/// The dual PDE supports both large (64KB) and small (4KB) page tables.
+#[repr(C)]
+#[derive(Debug, Clone, Copy, Default)]
+pub(crate) struct DualPde {
+    /// Large/Big Page Table pointer (lower 64 bits).
+    pub big: Pde,
+    /// Small Page Table pointer (upper 64 bits).
+    pub small: Pde,
+}
+
+impl DualPde {
+    /// Create a dual PDE from raw 128-bit value (two `u64`s).
+    pub(crate) fn new(big: u64, small: u64) -> Self {
+        Self {
+            big: Pde::new(big),
+            small: Pde::new(small),
+        }
+    }
+
+    /// Create a dual PDE with only the small page table pointer set.
+    ///
+    /// Note: The big (LPT) portion is set to 0, not `Pde::invalid()`.
+    /// According to hardware documentation, clearing bit 0 of the 128-bit
+    /// entry makes the PDE behave as a "normal" PDE. Using `Pde::invalid()`
+    /// would set bit 0 (valid_inverted), which breaks page table walking.
+    pub(crate) fn new_small(table_pfn: Pfn) -> Self {
+        Self {
+            big: Pde::new(0),
+            small: Pde::new_vram(table_pfn),
+        }
+    }
+
+    /// Check if the small page table pointer is valid.
+    pub(crate) fn has_small(&self) -> bool {
+        self.small.is_valid()
+    }
+
+    /// Check if the big page table pointer is valid.
+    pub(crate) fn has_big(&self) -> bool {
+        self.big.is_valid()
+    }
+
+    /// Get the small page table PFN.
+    pub(crate) fn small_pfn(&self) -> Pfn {
+        self.small.table_frame()
+    }
+}
-- 
2.34.1