[PATCH v9 20/23] gpu: nova-core: mm: Add BAR1 user interface

Joel Fernandes
2026-03-11T00:41:10Z

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/gpu.rs | 17 ++-
drivers/gpu/nova-core/gsp/commands.rs | 1 -
drivers/gpu/nova-core/mm.rs | 1 +
drivers/gpu/nova-core/mm/bar_user.rs | 156 ++++++++++++++++++++++++++
5 files changed, 173 insertions(+), 3 deletions(-)
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 b4311adf4cef..3bc264a099de 100644
--- a/drivers/gpu/nova-core/driver.rs
+++ b/drivers/gpu/nova-core/driver.rs
@@ -51,7 +51,6 @@ 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/gpu.rs b/drivers/gpu/nova-core/gpu.rs
index 32266480bb0f..efff76313b89 100644
--- a/drivers/gpu/nova-core/gpu.rs
+++ b/drivers/gpu/nova-core/gpu.rs
@@ -24,7 +24,12 @@
commands::GetGspStaticInfoReply,
Gsp, //
},
- mm::GpuMm,
+ mm::{
+ bar_user::BarUser,
+ pagetable::MmuVersion,
+ GpuMm,
+ VramAddress, //
+ },
regs,
};

@@ -263,6 +268,8 @@ pub(crate) struct Gpu {
gsp: Gsp,
/// Static GPU information from GSP.
gsp_static_info: GetGspStaticInfoReply,
+ /// BAR1 user interface for CPU access to GPU virtual memory.
+ bar_user: BarUser,
}

impl Gpu {
@@ -320,6 +327,14 @@ pub(crate) fn new<'a>(
}, pramin_vram_region)?
},

+ // Create BAR1 user interface for CPU access to GPU virtual memory.
+ bar_user: {
+ let pdb_addr = VramAddress::new(gsp_static_info.bar1_pde_base);
+ let mmu_version = MmuVersion::from(spec.chipset.arch());
+ let bar1_size = pdev.resource_len(1)?;
+ BarUser::new(pdb_addr, mmu_version, bar1_size)?
+ },
+
bar: devres_bar,
})
}
diff --git a/drivers/gpu/nova-core/gsp/commands.rs b/drivers/gpu/nova-core/gsp/commands.rs
index 1901c8928ab8..bfbe7bb05755 100644
--- a/drivers/gpu/nova-core/gsp/commands.rs
+++ b/drivers/gpu/nova-core/gsp/commands.rs
@@ -191,7 +191,6 @@ fn init(&self) -> impl Init<Self::Command, Self::InitError> {
pub(crate) struct GetGspStaticInfoReply {
gpu_name: [u8; 64],
/// BAR1 Page Directory Entry base address.
- #[expect(dead_code)]
pub(crate) bar1_pde_base: u64,
/// Usable FB (VRAM) region for driver memory allocation.
pub(crate) usable_fb_region: Range<u64>,
diff --git a/drivers/gpu/nova-core/mm.rs b/drivers/gpu/nova-core/mm.rs
index 6e58f597fadd..c053d4f3b26c 100644
--- a/drivers/gpu/nova-core/mm.rs
+++ b/drivers/gpu/nova-core/mm.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;
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..0d083f3e72c2
--- /dev/null
+++ b/drivers/gpu/nova-core/mm/bar_user.rs
@@ -0,0 +1,156 @@
+// 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,
+ prelude::*, //
+};
+
+use crate::{
+ driver::Bar1,
+ mm::{
+ pagetable::MmuVersion,
+ vmm::{
+ MappedRange,
+ Vmm, //
+ },
+ GpuMm,
+ Pfn,
+ Vfn,
+ VirtualAddress,
+ VramAddress,
+ PAGE_SIZE, //
+ },
+ num::IntoSafeCast,
+};
+
+/// 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 {
+ // `mapped` is only `None` after `take()` in `Drop`; accessors are
+ // never called from within `Drop`, so unwrap() never panics.
+ 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_vfn: usize = self.mapped().vfn_start.raw().into_safe_cast();
+ let base = base_vfn.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");
+ }
+ }
+ }
+}
--
2.34.1