Add the page table mapping and unmapping API to the Virtual Memory Manager, implementing a two-phase prepare/execute model suitable for use both inside and outside the DMA fence signalling critical path.
Cc: Nikola Djukic <[email protected]> Signed-off-by: Joel Fernandes <[email protected]> --- drivers/gpu/nova-core/mm/vmm.rs | 347 +++++++++++++++++++++++++++++++- 1 file changed, 345 insertions(+), 2 deletions(-) diff --git a/drivers/gpu/nova-core/mm/vmm.rs b/drivers/gpu/nova-core/mm/vmm.rs index 9e57916017ed..af3daccbf958 100644 --- a/drivers/gpu/nova-core/mm/vmm.rs +++ b/drivers/gpu/nova-core/mm/vmm.rs @@ -17,15 +17,25 @@ GpuBuddyParams, // }, prelude::*, + rbtree::{RBTree, RBTreeNode}, sizes::SZ_4K, // }; +use core::cell::Cell; use core::ops::Range; use crate::mm::{ pagetable::{ - walk::{PtWalk, WalkResult}, - MmuVersion, // + walk::{ + PtWalk, + WalkPdeResult, + WalkResult, // + }, + DualPde, + MmuVersion, + PageTableLevel, + Pde, + Pte, // }, GpuMm, Pfn, @@ -46,6 +56,74 @@ pub(crate) struct Vmm { page_table_allocs: KVec<Pin<KBox<AllocatedBlocks>>>, /// Buddy allocator for virtual address range tracking. virt_buddy: GpuBuddy, + /// Prepared PT pages pending PDE installation, keyed by `install_addr`. + /// + /// Populated by `Vmm` mapping prepare phase and drained in the execute phase. + /// Shared by all pending maps in the `Vmm`, thus preventing races where 2 + /// maps might be trying to install the same page table/directory entry pointer. + pt_pages: RBTree<VramAddress, PreparedPtPage>, +} + +/// A pre-allocated and zeroed page table page. +/// +/// Created during the mapping prepare phase and consumed during the mapping execute phase. +/// Stored in an [`RBTree`] keyed by the PDE slot address (`install_addr`). +struct PreparedPtPage { + /// The allocated and zeroed page table page. + alloc: Pin<KBox<AllocatedBlocks>>, + /// Page table level -- needed to determine if this PT page is for a dual PDE. + level: PageTableLevel, +} + +/// Multi-page prepared mapping -- VA range allocated, ready for execute. +/// +/// Produced by [`Vmm::prepare_map()`], consumed by [`Vmm::execute_map()`]. +/// The struct owns the VA space allocation between prepare and execute phases. +pub(crate) struct PreparedMapping { + vfn_start: Vfn, + num_pages: usize, + vfn_alloc: Pin<KBox<AllocatedBlocks>>, +} + +/// Result of a mapping operation -- tracks the active mapped range. +/// +/// Returned by [`Vmm::execute_map()`] and [`Vmm::map_pages()`]. +/// Owns the VA allocation; the VA range is freed when this is dropped. +/// Callers must call [`Vmm::unmap_pages()`] before dropping to invalidate +/// PTEs (dropping only frees the VA range, not the PTE entries). +pub(crate) struct MappedRange { + pub(crate) vfn_start: Vfn, + pub(crate) num_pages: usize, + /// VA allocation -- freed when [`MappedRange`] is dropped. + _vfn_alloc: Pin<KBox<AllocatedBlocks>>, + /// Logs a warning if dropped without unmapping. + _drop_guard: MustUnmapGuard, +} + +/// Guard that logs a warning once if a [`MappedRange`] is dropped without +/// calling [`Vmm::unmap_pages()`]. +struct MustUnmapGuard { + armed: Cell<bool>, +} + +impl MustUnmapGuard { + const fn new() -> Self { + Self { + armed: Cell::new(true), + } + } + + fn disarm(&self) { + self.armed.set(false); + } +} + +impl Drop for MustUnmapGuard { + fn drop(&mut self) { + if self.armed.get() { + kernel::pr_warn_once!("MappedRange dropped without calling unmap_pages()\n"); + } + } } impl Vmm { @@ -72,6 +150,7 @@ pub(crate) fn new( mmu_version, page_table_allocs: KVec::new(), virt_buddy, + pt_pages: RBTree::new(), }) } @@ -127,4 +206,268 @@ pub(crate) fn read_mapping(&self, mm: &GpuMm, vfn: Vfn) -> Result<Option<Pfn>> { WalkResult::Unmapped { .. } | WalkResult::PageTableMissing => Ok(None), } } + + /// Allocate and zero a physical page table page for a specific PDE slot. + /// Called during the map prepare phase. + fn alloc_and_zero_page_table( + &mut self, + mm: &GpuMm, + level: PageTableLevel, + ) -> Result<PreparedPtPage> { + let params = GpuBuddyAllocParams { + start_range_address: 0, + end_range_address: 0, + size_bytes: SZ_4K as u64, + min_block_size_bytes: SZ_4K as u64, + buddy_flags: BuddyFlags::try_new(0)?, + }; + let blocks = KBox::pin_init(mm.buddy().alloc_blocks(¶ms), GFP_KERNEL)?; + + // Get page's VRAM address from the allocation. + let page_vram = VramAddress::new(blocks.iter().next().ok_or(ENOMEM)?.offset()); + + // Zero via PRAMIN. + let mut window = mm.pramin().window()?; + let base = page_vram.raw(); + for off in (0..PAGE_SIZE).step_by(8) { + window.try_write64(base + off, 0)?; + } + + Ok(PreparedPtPage { + alloc: blocks, + level, + }) + } + + /// Ensure all intermediate page table pages are prepared for a [`Vfn`]. Just + /// finds out which PDE pages are missing, allocates pages for them, and defers + /// installation to the execute phase. + /// + /// PRAMIN is released before each allocation and re-acquired after. Memory + /// allocations outside of holding this lock to prevent deadlocks with fence signalling + /// critical path. + fn ensure_pte_path(&mut self, mm: &GpuMm, vfn: Vfn) -> Result { + let walker = PtWalk::new(self.pdb_addr, self.mmu_version); + let max_iter = 2 * self.mmu_version.pde_level_count(); + + // Keep looping until all PDE levels are resolved. + for _ in 0..max_iter { + let mut window = mm.pramin().window()?; + + // Walk PDE levels. The closure checks self.pt_pages for prepared-but-uninstalled + // pages, letting the walker continue through them as if they were installed in HW. + // The walker keeps calling the closure to get these "prepared but not installed" pages. + let result = walker.walk_pde_levels(&mut window, vfn, |install_addr| { + self.pt_pages + .get(&install_addr) + .and_then(|p| Some(VramAddress::new(p.alloc.iter().next()?.offset()))) + })?; + + match result { + WalkPdeResult::Complete { .. } => { + // All PDE levels resolved. + return Ok(()); + } + WalkPdeResult::Missing { + install_addr, + level, + } => { + // Drop PRAMIN before allocation. + drop(window); + let page = self.alloc_and_zero_page_table(mm, level)?; + let node = RBTreeNode::new(install_addr, page, GFP_KERNEL)?; + let old = self.pt_pages.insert(node); + if old.is_some() { + kernel::pr_warn_once!( + "VMM: duplicate install_addr in pt_pages (internal consistency error)\n" + ); + return Err(EIO); + } + // Loop: re-acquire PRAMIN and re-walk from root. + } + } + } + + Err(EIO) + } + + /// Prepare resources for mapping `num_pages` pages. + /// + /// Allocates a contiguous VA range, then walks the hierarchy per-VFN to prepare pages + /// for all missing PDEs. Returns a [`PreparedMapping`] with the VA allocation. + /// + /// If `va_range` is not `None`, the VA range is constrained to the given range. Safe + /// to call outside the fence signalling critical path. + pub(crate) fn prepare_map( + &mut self, + mm: &GpuMm, + num_pages: usize, + va_range: Option<Range<u64>>, + ) -> Result<PreparedMapping> { + if num_pages == 0 { + return Err(EINVAL); + } + + // Pre-reserve so execute_map() can use push_within_capacity (no alloc in + // fence signalling critical path). + // Upper bound on page table pages needed for the full tree (PTE pages + PDE + // pages at all levels). + let pt_upper_bound = self.mmu_version.pt_pages_upper_bound(num_pages); + self.page_table_allocs.reserve(pt_upper_bound, GFP_KERNEL)?; + + // Allocate contiguous VA range. + let (vfn_start, vfn_alloc) = self.alloc_vfn_range(num_pages, va_range)?; + + // Walk the hierarchy per-VFN to prepare pages for all missing PDEs. + for i in 0..num_pages { + let vfn = Vfn::new(vfn_start.raw() + i as u64); + self.ensure_pte_path(mm, vfn)?; + } + + Ok(PreparedMapping { + vfn_start, + num_pages, + vfn_alloc, + }) + } + + /// Execute a prepared multi-page mapping. + /// + /// Drain prepared PT pages and install PDEs followed by single TLB flush. + pub(crate) fn execute_map( + &mut self, + mm: &GpuMm, + prepared: PreparedMapping, + pfns: &[Pfn], + writable: bool, + ) -> Result<MappedRange> { + if pfns.len() != prepared.num_pages { + return Err(EINVAL); + } + + let PreparedMapping { + vfn_start, + num_pages, + vfn_alloc, + } = prepared; + + let walker = PtWalk::new(self.pdb_addr, self.mmu_version); + let mut window = mm.pramin().window()?; + + // First, drain self.pt_pages, install all pending PDEs. + let mut cursor = self.pt_pages.cursor_front_mut(); + while let Some(c) = cursor { + let (next, node) = c.remove_current(); + let (install_addr, page) = node.to_key_value(); + let page_vram = VramAddress::new(page.alloc.iter().next().ok_or(ENOMEM)?.offset()); + + if page.level == self.mmu_version.dual_pde_level() { + let new_dpde = DualPde::new_small(self.mmu_version, Pfn::from(page_vram)); + new_dpde.write(&mut window, install_addr)?; + } else { + let new_pde = Pde::new_vram(self.mmu_version, Pfn::from(page_vram)); + new_pde.write(&mut window, install_addr)?; + } + + // Track the allocated pages in the `Vmm`. + self.page_table_allocs + .push_within_capacity(page.alloc) + .map_err(|_| ENOMEM)?; + + cursor = next; + } + + // Next, write PTEs (all PDEs now installed in HW). + for (i, &pfn) in pfns.iter().enumerate() { + let vfn = Vfn::new(vfn_start.raw() + i as u64); + let result = walker.walk_to_pte_lookup_with_window(&mut window, vfn)?; + + match result { + WalkResult::Unmapped { pte_addr } | WalkResult::Mapped { pte_addr, .. } => { + let pte = Pte::new_vram(self.mmu_version, pfn, writable); + pte.write(&mut window, pte_addr)?; + } + WalkResult::PageTableMissing => { + kernel::pr_warn_once!("VMM: page table missing for VFN {vfn:?}\n"); + return Err(EIO); + } + } + } + + drop(window); + + // Finally, flush the TLB. + mm.tlb().flush(self.pdb_addr)?; + + Ok(MappedRange { + vfn_start, + num_pages, + _vfn_alloc: vfn_alloc, + _drop_guard: MustUnmapGuard::new(), + }) + } + + /// Map pages doing prepare and execute in the same call. + /// + /// This is a convenience wrapper for callers outside the fence signalling critical + /// path (e.g., BAR mappings). For DRM usecases, [`Vmm::prepare_map()`] and + /// [`Vmm::execute_map()`] will be called separately. + pub(crate) fn map_pages( + &mut self, + mm: &GpuMm, + pfns: &[Pfn], + va_range: Option<Range<u64>>, + writable: bool, + ) -> Result<MappedRange> { + if pfns.is_empty() { + return Err(EINVAL); + } + + // Check if provided VA range is sufficient (if provided). + if let Some(ref range) = va_range { + let required = pfns.len().checked_mul(PAGE_SIZE).ok_or(EOVERFLOW)? as u64; + let available = range.end.checked_sub(range.start).ok_or(EINVAL)?; + if available < required { + return Err(EINVAL); + } + } + + let prepared = self.prepare_map(mm, pfns.len(), va_range)?; + self.execute_map(mm, prepared, pfns, writable) + } + + /// Unmap all pages in a [`MappedRange`] with a single TLB flush. + /// + /// Takes the range by value (consumes it), then invalidates PTEs for the range, + /// flushes the TLB, then drops the range (freeing the VA). PRAMIN lock is held. + pub(crate) fn unmap_pages(&mut self, mm: &GpuMm, range: MappedRange) -> Result { + let walker = PtWalk::new(self.pdb_addr, self.mmu_version); + let invalid_pte = Pte::invalid(self.mmu_version); + + let mut window = mm.pramin().window()?; + for i in 0..range.num_pages { + let vfn = Vfn::new(range.vfn_start.raw() + i as u64); + let result = walker.walk_to_pte_lookup_with_window(&mut window, vfn)?; + + match result { + WalkResult::Mapped { pte_addr, .. } | WalkResult::Unmapped { pte_addr } => { + invalid_pte.write(&mut window, pte_addr)?; + } + WalkResult::PageTableMissing => { + continue; + } + } + } + drop(window); + + mm.tlb().flush(self.pdb_addr)?; + + // TODO: Internal page table pages (PDE, PTE pages) are still kept around. + // This is by design as repeated maps/unmaps will be fast. As a future TODO, + // we can add a reclaimer here to reclaim if VRAM is short. For now, the PT + // pages are dropped once the `Vmm` is dropped. + + range._drop_guard.disarm(); // Unmap complete, Ok to drop MappedRange. + Ok(()) + } } -- 2.34.1
