From: Tim Kovalenko <[email protected]> The `Cmdq::new` function was allocating a `PteArray` struct on the stack and was causing a stack overflow with 8216 bytes.
Remove the `PteArray` and instead calculate and write the Page Table Entries directly into the coherent DMA buffer one-by-one. This reduces the stack usage quite a lot. Signed-off-by: Tim Kovalenko <[email protected]> --- Changes in v2: - Missed a code formatting issue. - Link to v1: https://lore.kernel.org/r/[email protected] --- drivers/gpu/nova-core/gsp.rs | 50 ++++++++++++++------------------------- drivers/gpu/nova-core/gsp/cmdq.rs | 27 ++++++++++++++++++--- 2 files changed, 42 insertions(+), 35 deletions(-) diff --git a/drivers/gpu/nova-core/gsp.rs b/drivers/gpu/nova-core/gsp.rs index 174feaca0a6b9269cf35286dec3acc4d60918904..316eeaf87ec5ae67422a34426eefa747c9b6502b 100644 --- a/drivers/gpu/nova-core/gsp.rs +++ b/drivers/gpu/nova-core/gsp.rs @@ -2,16 +2,14 @@ mod boot; +use core::iter::Iterator; + use kernel::{ device, - dma::{ - CoherentAllocation, - DmaAddress, // - }, + dma::CoherentAllocation, dma_write, pci, - prelude::*, - transmute::AsBytes, // + prelude::*, // }; pub(crate) mod cmdq; @@ -39,27 +37,6 @@ /// Number of GSP pages to use in a RM log buffer. const RM_LOG_BUFFER_NUM_PAGES: usize = 0x10; -/// Array of page table entries, as understood by the GSP bootloader. -#[repr(C)] -struct PteArray<const NUM_ENTRIES: usize>([u64; NUM_ENTRIES]); - -/// SAFETY: arrays of `u64` implement `AsBytes` and we are but a wrapper around one. -unsafe impl<const NUM_ENTRIES: usize> AsBytes for PteArray<NUM_ENTRIES> {} - -impl<const NUM_PAGES: usize> PteArray<NUM_PAGES> { - /// Creates a new page table array mapping `NUM_PAGES` GSP pages starting at address `start`. - fn new(start: DmaAddress) -> Result<Self> { - let mut ptes = [0u64; NUM_PAGES]; - for (i, pte) in ptes.iter_mut().enumerate() { - *pte = start - .checked_add(num::usize_as_u64(i) << GSP_PAGE_SHIFT) - .ok_or(EOVERFLOW)?; - } - - Ok(Self(ptes)) - } -} - /// The logging buffers are byte queues that contain encoded printf-like /// messages from GSP-RM. They need to be decoded by a special application /// that can parse the buffers. @@ -86,16 +63,25 @@ fn new(dev: &device::Device<device::Bound>) -> Result<Self> { NUM_PAGES * GSP_PAGE_SIZE, GFP_KERNEL | __GFP_ZERO, )?); - let ptes = PteArray::<NUM_PAGES>::new(obj.0.dma_handle())?; + + let start_addr = obj.0.dma_handle(); // SAFETY: `obj` has just been created and we are its sole user. - unsafe { - // Copy the self-mapping PTE at the expected location. + let pte_region = unsafe { obj.0 - .as_slice_mut(size_of::<u64>(), size_of_val(&ptes))? - .copy_from_slice(ptes.as_bytes()) + .as_slice_mut(size_of::<u64>(), NUM_PAGES * size_of::<u64>())? }; + // As in [`DmaGspMem`], this is a one by one GSP Page write to the memory + // to avoid stack overflow when allocating the whole array at once. + for (i, chunk) in pte_region.chunks_exact_mut(size_of::<u64>()).enumerate() { + let pte_value = start_addr + .checked_add(num::usize_as_u64(i) << GSP_PAGE_SHIFT) + .ok_or(EOVERFLOW)?; + + chunk.copy_from_slice(&pte_value.to_ne_bytes()); + } + Ok(obj) } } diff --git a/drivers/gpu/nova-core/gsp/cmdq.rs b/drivers/gpu/nova-core/gsp/cmdq.rs index 46819a82a51adc58423502d9d45730923b843656..7a6cb261f4e62ac6210a80f9ecb61213cdb91b15 100644 --- a/drivers/gpu/nova-core/gsp/cmdq.rs +++ b/drivers/gpu/nova-core/gsp/cmdq.rs @@ -35,7 +35,6 @@ MsgqRxHeader, MsgqTxHeader, // }, - PteArray, GSP_PAGE_SHIFT, GSP_PAGE_SIZE, // }, @@ -159,7 +158,7 @@ struct Msgq { #[repr(C)] struct GspMem { /// Self-mapping page table entries. - ptes: PteArray<{ GSP_PAGE_SIZE / size_of::<u64>() }>, + ptes: [u64; GSP_PAGE_SIZE / size_of::<u64>()], /// CPU queue: the driver writes commands here, and the GSP reads them. It also contains the /// write and read pointers that the CPU updates. /// @@ -201,7 +200,29 @@ fn new(dev: &device::Device<device::Bound>) -> Result<Self> { let gsp_mem = CoherentAllocation::<GspMem>::alloc_coherent(dev, 1, GFP_KERNEL | __GFP_ZERO)?; - dma_write!(gsp_mem[0].ptes = PteArray::new(gsp_mem.dma_handle())?)?; + const NUM_PAGES: usize = GSP_PAGE_SIZE / size_of::<u64>(); + + // One by one GSP Page write to the memory to avoid stack overflow when allocating + // the whole array at once. + let item = gsp_mem.item_from_index(0)?; + for i in 0..NUM_PAGES { + let pte_value = gsp_mem + .dma_handle() + .checked_add(num::usize_as_u64(i) << GSP_PAGE_SHIFT) + .ok_or(EOVERFLOW)?; + + // SAFETY: `item_from_index` ensures that `item` is always a valid pointer and can be + // dereferenced. The compiler also further validates the expression on whether `field` + // is a member of `item` when expanded by the macro. + // + // Further, this is dma_write! macro expanded and modified to allow for individual + // page write. + unsafe { + let ptr_field = core::ptr::addr_of_mut!((*item).ptes[i]); + gsp_mem.field_write(ptr_field, pte_value); + } + } + dma_write!(gsp_mem[0].cpuq.tx = MsgqTxHeader::new(MSGQ_SIZE, RX_HDR_OFF, MSGQ_NUM_PAGES))?; dma_write!(gsp_mem[0].cpuq.rx = MsgqRxHeader::new())?; --- base-commit: cea7b66a80412e2a5b74627b89ae25f1d0110a4b change-id: 20260212-drm-rust-next-beb92aee9d75 Best regards, -- Tim Kovalenko <[email protected]>
