[PATCH v3 08/31] gpu: nova-core: mm: borrow BarUser for temporary BAR1 access

[Zhi Wang <zhiw@nvidia.com>]

Temporary BAR1 access needs a borrow of the GPU-owned BarUser. Store
BarUser inline in Gpu and borrow it in BarUserAccess, avoiding a separate
allocation and reference counting for these accesses. Update the existing
self-test entry points to accept the borrowed interface.

No functional change is intended.

Cc: Alistair Popple <apopple@nvidia.com>
Signed-off-by: Zhi Wang <zhiw@nvidia.com>
---
 drivers/gpu/nova-core/gpu.rs         | 21 +++++++++------------
 drivers/gpu/nova-core/mm.rs          |  5 ++---
 drivers/gpu/nova-core/mm/bar_user.rs | 27 ++++++++++++---------------
 3 files changed, 23 insertions(+), 30 deletions(-)

diff --git a/drivers/gpu/nova-core/gpu.rs b/drivers/gpu/nova-core/gpu.rs
index 11d9986c4b19..97b33d4b2631 100644
--- a/drivers/gpu/nova-core/gpu.rs
+++ b/drivers/gpu/nova-core/gpu.rs
@@ -16,7 +16,6 @@
         SizeConstants,
         SZ_4K, //
     },
-    sync::Arc,
 };
 
 use crate::{
@@ -340,7 +339,8 @@ pub(crate) struct Gpu<'gpu> {
     /// the GSP is still operational.
     mm: GpuMm<'gpu>,
     /// BAR1 user interface for CPU access to GPU virtual memory.
-    bar_user: Arc<BarUser<'gpu>>,
+    #[pin]
+    bar_user: BarUser<'gpu>,
     /// GSP and its resources.
     #[pin]
     gsp_resources: GspResources<'gpu>,
@@ -545,18 +545,15 @@ pub(crate) fn new<'a>(
             },
 
             // Create BAR1 user interface for CPU access to GPU virtual memory.
-            bar_user: {
+            bar_user <- {
                 let pdb_addr = VramAddress::from_raw(gsp_resources.static_info().bar1_pde_base());
                 let bar1_idx = crate::driver::bar1_resource_index(pdev)?;
                 let bar1_size = pdev.resource_len(bar1_idx)?;
-                Arc::pin_init(
-                    BarUser::new(
-                        pdb_addr,
-                        gsp_resources.spec.chipset,
-                        bar1_size,
-                        bar1,
-                    )?,
-                    GFP_KERNEL,
+                BarUser::new(
+                    pdb_addr,
+                    gsp_resources.spec.chipset,
+                    bar1_size,
+                    bar1,
                 )?
             },
         })
@@ -573,7 +570,7 @@ pub(crate) fn run_selftests(self: Pin<&mut Self>, pdev: &pci::Device<device::Bou
             dev,
             this.mm,
             info.usable_fb_regions(),
-            this.bar_user,
+            this.bar_user.as_ref().get_ref(),
             info.bar1_pde_base(),
             this.spec.chipset,
         ) {
diff --git a/drivers/gpu/nova-core/mm.rs b/drivers/gpu/nova-core/mm.rs
index ea85c821f0e2..a835180db6c5 100644
--- a/drivers/gpu/nova-core/mm.rs
+++ b/drivers/gpu/nova-core/mm.rs
@@ -298,8 +298,7 @@ pub(crate) mod selftest {
 
     use kernel::{
         device,
-        sizes::SizeConstants,
-        sync::Arc, //
+        sizes::SizeConstants, //
     };
 
     use super::*;
@@ -309,7 +308,7 @@ pub(crate) fn run(
         dev: &device::Device<device::Bound>,
         mm: &mut GpuMm<'_>,
         mut usable_fb_regions: impl Iterator<Item = Range<u64>>,
-        bar_user: &Arc<bar_user::BarUser<'_>>,
+        bar_user: &bar_user::BarUser<'_>,
         bar1_pdb: u64,
         chipset: Chipset,
     ) -> Result {
diff --git a/drivers/gpu/nova-core/mm/bar_user.rs b/drivers/gpu/nova-core/mm/bar_user.rs
index cd2d0271e64c..414c69e037ee 100644
--- a/drivers/gpu/nova-core/mm/bar_user.rs
+++ b/drivers/gpu/nova-core/mm/bar_user.rs
@@ -7,10 +7,7 @@
     io::Io,
     new_mutex,
     prelude::*,
-    sync::{
-        Arc,
-        Mutex, //
-    },
+    sync::Mutex, //
 };
 
 use crate::{
@@ -60,12 +57,12 @@ pub(crate) fn new(
     }
 
     /// Map physical pages to a contiguous BAR1 virtual range.
-    pub(crate) fn map(
-        self: &Arc<Self>,
+    pub(crate) fn map<'access>(
+        &'access self,
         mm: &mut GpuMm<'_>,
         pfns: &[Pfn],
         writable: bool,
-    ) -> Result<BarUserAccess<'gpu>> {
+    ) -> Result<BarUserAccess<'access, 'gpu>> {
         if pfns.is_empty() {
             return Err(EINVAL);
         }
@@ -73,21 +70,21 @@ pub(crate) fn map(
         let mapped = vmm.map_pages(mm, pfns, None, writable)?;
 
         Ok(BarUserAccess {
-            bar_user: self.clone(),
+            bar_user: self,
             mapped: Some(mapped),
         })
     }
 }
 
 /// Access object for a mapped BAR1 region.
-pub(crate) struct BarUserAccess<'gpu> {
-    bar_user: Arc<BarUser<'gpu>>,
+pub(crate) struct BarUserAccess<'access, 'gpu> {
+    bar_user: &'access BarUser<'gpu>,
     /// Cleared only after PTE invalidation and its TLB flush succeed.
     mapped: Option<MappedRange>,
 }
 
 #[expect(dead_code)]
-impl BarUserAccess<'_> {
+impl BarUserAccess<'_, '_> {
     /// Tear down the BAR1 mapping.
     pub(crate) fn release(mut self, mm: &mut GpuMm<'_>) -> Result {
         self.unmap(mm)
@@ -167,7 +164,7 @@ pub(crate) fn try_write64(&self, value: u64, offset: usize) -> Result {
     }
 }
 
-impl Drop for BarUserAccess<'_> {
+impl Drop for BarUserAccess<'_, '_> {
     fn drop(&mut self) {
         if self.mapped.is_some() {
             kernel::pr_warn!(
@@ -185,10 +182,10 @@ fn drop(&mut self) {
 /// address space. Uses the `GpuMm`'s buddy allocator to allocate page tables
 /// and test pages as needed.
 #[cfg(CONFIG_NOVA_CORE_SELFTESTS)]
-pub(crate) fn run_self_test(
+pub(super) fn run_self_test(
     dev: &device::Device<device::Bound>,
     mm: &mut GpuMm<'_>,
-    bar_user: &Arc<BarUser<'_>>,
+    bar_user: &BarUser<'_>,
     bar1_pdb: u64,
     chipset: Chipset,
 ) -> Result {
@@ -401,7 +398,7 @@ pub(crate) fn run_self_test(
     drop(vmm);
 
     // Test 4: Exercise `BarUser::map()` end-to-end.
-    let bar_user = Arc::pin_init(
+    let bar_user = KBox::pin_init(
         BarUser::new(pdb_addr, chipset, SZ_64K.into_safe_cast(), bar1)?,
         GFP_KERNEL,
     )?;