[PATCH v7 16/23] nova-core: mm: Add BAR1 user interface

[Joel Fernandes <joelagnelf@nvidia.com>]

Add the BAR1 user interface for CPU access to GPU video memory through
the BAR1 aperture.

Cc: Nikola Djukic <ndjukic@nvidia.com>
Signed-off-by: Joel Fernandes <joelagnelf@nvidia.com>
---
 drivers/gpu/nova-core/driver.rs      |   1 -
 drivers/gpu/nova-core/mm/bar_user.rs | 154 +++++++++++++++++++++++++++
 drivers/gpu/nova-core/mm/mod.rs      |   1 +
 3 files changed, 155 insertions(+), 1 deletion(-)
 create mode 100644 drivers/gpu/nova-core/mm/bar_user.rs

diff --git a/drivers/gpu/nova-core/driver.rs b/drivers/gpu/nova-core/driver.rs
index f30ffa45cf13..d8b2e967ba4c 100644
--- a/drivers/gpu/nova-core/driver.rs
+++ b/drivers/gpu/nova-core/driver.rs
@@ -42,7 +42,6 @@ pub(crate) struct NovaCore {
 const GPU_DMA_BITS: u32 = 47;
 
 pub(crate) type Bar0 = pci::Bar<BAR0_SIZE>;
-#[expect(dead_code)]
 pub(crate) type Bar1 = pci::Bar<BAR1_SIZE>;
 
 kernel::pci_device_table!(
diff --git a/drivers/gpu/nova-core/mm/bar_user.rs b/drivers/gpu/nova-core/mm/bar_user.rs
new file mode 100644
index 000000000000..74119c4d365e
--- /dev/null
+++ b/drivers/gpu/nova-core/mm/bar_user.rs
@@ -0,0 +1,154 @@
+// SPDX-License-Identifier: GPL-2.0
+
+//! BAR1 user interface for CPU access to GPU virtual memory. Used for USERD
+//! for GPU work submission, and applications to access GPU buffers via mmap().
+
+use kernel::io::Io;
+use kernel::prelude::*;
+
+use crate::{
+    driver::Bar1,
+    mm::{
+        pagetable::MmuVersion,
+        vmm::{
+            MappedRange,
+            Vmm, //
+        },
+        GpuMm,
+        Pfn,
+        Vfn,
+        VirtualAddress,
+        VramAddress,
+        PAGE_SIZE, //
+    },
+};
+
+/// BAR1 user interface for virtual memory mappings.
+///
+/// Owns a VMM instance with virtual address tracking and provides
+/// BAR1-specific mapping and cleanup operations.
+pub(crate) struct BarUser {
+    vmm: Vmm,
+}
+
+impl BarUser {
+    /// Create a new [`BarUser`] with virtual address tracking.
+    pub(crate) fn new(
+        pdb_addr: VramAddress,
+        mmu_version: MmuVersion,
+        va_size: u64,
+    ) -> Result<Self> {
+        Ok(Self {
+            vmm: Vmm::new(pdb_addr, mmu_version, va_size)?,
+        })
+    }
+
+    /// Map physical pages to a contiguous BAR1 virtual range.
+    pub(crate) fn map<'a>(
+        &'a mut self,
+        mm: &'a GpuMm,
+        bar: &'a Bar1,
+        pfns: &[Pfn],
+        writable: bool,
+    ) -> Result<BarAccess<'a>> {
+        if pfns.is_empty() {
+            return Err(EINVAL);
+        }
+
+        let mapped = self.vmm.map_pages(mm, pfns, None, writable)?;
+
+        Ok(BarAccess {
+            vmm: &mut self.vmm,
+            mm,
+            bar,
+            mapped: Some(mapped),
+        })
+    }
+}
+
+/// Access object for a mapped BAR1 region.
+///
+/// Wraps a [`MappedRange`] and provides BAR1 access. When dropped,
+/// unmaps pages and releases the VA range (by passing the range to
+/// [`Vmm::unmap_pages()`], which consumes it).
+pub(crate) struct BarAccess<'a> {
+    vmm: &'a mut Vmm,
+    mm: &'a GpuMm,
+    bar: &'a Bar1,
+    /// Needs to be an `Option` so that we can `take()` it and call `Drop`
+    /// on it in [`Vmm::unmap_pages()`].
+    mapped: Option<MappedRange>,
+}
+
+impl<'a> BarAccess<'a> {
+    /// Returns the active mapping.
+    fn mapped(&self) -> &MappedRange {
+        // SAFETY: unwrap() will never panic here because `mapped` is only
+        // `None` after `take()` in `Drop`, accessors are never called in `Drop`.
+        self.mapped.as_ref().unwrap()
+    }
+
+    /// Get the base virtual address of this mapping.
+    pub(crate) fn base(&self) -> VirtualAddress {
+        VirtualAddress::from(self.mapped().vfn_start)
+    }
+
+    /// Get the total size of the mapped region in bytes.
+    pub(crate) fn size(&self) -> usize {
+        self.mapped().num_pages * PAGE_SIZE
+    }
+
+    /// Get the starting virtual frame number.
+    pub(crate) fn vfn_start(&self) -> Vfn {
+        self.mapped().vfn_start
+    }
+
+    /// Get the number of pages in this mapping.
+    pub(crate) fn num_pages(&self) -> usize {
+        self.mapped().num_pages
+    }
+
+    /// Translate an offset within this mapping to a BAR1 aperture offset.
+    fn bar_offset(&self, offset: usize) -> Result<usize> {
+        if offset >= self.size() {
+            return Err(EINVAL);
+        }
+
+        let base = (self.mapped().vfn_start.raw() as usize)
+            .checked_mul(PAGE_SIZE)
+            .ok_or(EOVERFLOW)?;
+        base.checked_add(offset).ok_or(EOVERFLOW)
+    }
+
+    // Fallible accessors with runtime bounds checking.
+
+    /// Read a 32-bit value at the given offset.
+    pub(crate) fn try_read32(&self, offset: usize) -> Result<u32> {
+        self.bar.try_read32(self.bar_offset(offset)?)
+    }
+
+    /// Write a 32-bit value at the given offset.
+    pub(crate) fn try_write32(&self, value: u32, offset: usize) -> Result {
+        self.bar.try_write32(value, self.bar_offset(offset)?)
+    }
+
+    /// Read a 64-bit value at the given offset.
+    pub(crate) fn try_read64(&self, offset: usize) -> Result<u64> {
+        self.bar.try_read64(self.bar_offset(offset)?)
+    }
+
+    /// Write a 64-bit value at the given offset.
+    pub(crate) fn try_write64(&self, value: u64, offset: usize) -> Result {
+        self.bar.try_write64(value, self.bar_offset(offset)?)
+    }
+}
+
+impl Drop for BarAccess<'_> {
+    fn drop(&mut self) {
+        if let Some(mapped) = self.mapped.take() {
+            if self.vmm.unmap_pages(self.mm, mapped).is_err() {
+                kernel::pr_warn_once!("BarAccess: unmap_pages failed.\n");
+            }
+        }
+    }
+}
diff --git a/drivers/gpu/nova-core/mm/mod.rs b/drivers/gpu/nova-core/mm/mod.rs
index 922479accba6..b00f30641ab5 100644
--- a/drivers/gpu/nova-core/mm/mod.rs
+++ b/drivers/gpu/nova-core/mm/mod.rs
@@ -4,6 +4,7 @@
 
 #![expect(dead_code)]
 
+pub(crate) mod bar_user;
 pub(crate) mod pagetable;
 pub(crate) mod pramin;
 pub(crate) mod tlb;
-- 
2.34.1