Re: [PATCH v4 10/11] gpu: nova-core: align LibosMemoryRegionInitArgument size to page size

["Alexandre Courbot" <acourbot@nvidia.com>]

On Thu Dec 18, 2025 at 12:29 PM JST, Timur Tabi wrote:
> On Turing and GA100 (i.e. the versions that use Libos v2), GSP-RM insists
> that the 'size' parameter of the LibosMemoryRegionInitArgument struct be
> aligned to 4KB.  The logging buffers are already aligned to that size, so
> only the GSP_ARGUMENTS_CACHED struct needs to be adjusted.  Make that
> adjustment by adding padding to the end of the struct.
>
> Signed-off-by: Timur Tabi <ttabi@nvidia.com>
> ---
>  drivers/gpu/nova-core/gsp/fw.rs | 24 +++++++++++++++++-------
>  1 file changed, 17 insertions(+), 7 deletions(-)
>
> diff --git a/drivers/gpu/nova-core/gsp/fw.rs b/drivers/gpu/nova-core/gsp/fw.rs
> index abffd6beec65..ab3ad038889c 100644
> --- a/drivers/gpu/nova-core/gsp/fw.rs
> +++ b/drivers/gpu/nova-core/gsp/fw.rs
> @@ -889,17 +889,27 @@ unsafe impl AsBytes for GspMsgElement {}
>  unsafe impl FromBytes for GspMsgElement {}
>  
>  /// Arguments for GSP startup.
> -#[repr(transparent)]
> -pub(crate) struct GspArgumentsCached(bindings::GSP_ARGUMENTS_CACHED);
> +///
> +/// On Turing and GA100, the entries in the `LibosMemoryRegionInitArgument`
> +/// must all be a multiple of GSP_PAGE_SIZE in size, so add padding to force it
> +/// to that size.
> +#[repr(C)]
> +pub(crate) struct GspArgumentsCached(
> +    bindings::GSP_ARGUMENTS_CACHED,
> +    [u8; GSP_PAGE_SIZE - core::mem::size_of::<bindings::GSP_ARGUMENTS_CACHED>()],
> +);

In gsp.rs we are still initializing the rmarg as follows:

    dma_write!(rmargs[0] = fw::GspArgumentsCached::new(&cmdq))?;

Which passes the `GspArgumentsCached` queue by value to
`CoherentAllocation::field_write`, i.e. 4KB on the stack.

So I think the proper approach is to keep `GspArgumentsCached` as-is,
and use a different type just for allocation:

diff --git a/drivers/gpu/nova-core/gsp.rs b/drivers/gpu/nova-core/gsp.rs
index fb6f74797178..0feaff5784a7 100644
--- a/drivers/gpu/nova-core/gsp.rs
+++ b/drivers/gpu/nova-core/gsp.rs
@@ -25,10 +25,9 @@
 };

 use crate::{
-    gsp::cmdq::Cmdq,
-    gsp::fw::{
-        GspArgumentsCached,
-        LibosMemoryRegionInitArgument, //
+    gsp::{
+        cmdq::Cmdq,
+        fw::LibosMemoryRegionInitArgument, //
     },
     num,
 };
@@ -114,7 +113,7 @@ pub(crate) struct Gsp {
     /// Command queue.
     pub(crate) cmdq: Cmdq,
     /// RM arguments.
-    rmargs: CoherentAllocation<GspArgumentsCached>,
+    rmargs: CoherentAllocation<fw::GspArgumentsAligned>,
 }

 impl Gsp {
@@ -141,12 +140,12 @@ pub(crate) fn new(pdev: &pci::Device<device::Bound>) -> Result<impl PinInit<Self

         let cmdq = Cmdq::new(dev)?;

-        let rmargs = CoherentAllocation::<GspArgumentsCached>::alloc_coherent(
+        let rmargs = CoherentAllocation::<fw::GspArgumentsAligned>::alloc_coherent(
             dev,
             1,
             GFP_KERNEL | __GFP_ZERO,
         )?;
-        dma_write!(rmargs[0] = fw::GspArgumentsCached::new(&cmdq))?;
+        dma_write!(rmargs[0].inner = fw::GspArgumentsCached::new(&cmdq))?;
         dma_write!(libos[3] = LibosMemoryRegionInitArgument::new("RMARGS", &rmargs))?;

         Ok(try_pin_init!(Self {
diff --git a/drivers/gpu/nova-core/gsp/fw.rs b/drivers/gpu/nova-core/gsp/fw.rs
index abffd6beec65..15ca9c183ae1 100644
--- a/drivers/gpu/nova-core/gsp/fw.rs
+++ b/drivers/gpu/nova-core/gsp/fw.rs
@@ -906,9 +906,21 @@ pub(crate) fn new(cmdq: &Cmdq) -> Self {
 // SAFETY: Padding is explicit and will not contain uninitialized data.
 unsafe impl AsBytes for GspArgumentsCached {}

+/// On Turing and GA100, the entries in the `LibosMemoryRegionInitArgument`
+/// must all be a multiple of GSP_PAGE_SIZE in size, so add padding to force it
+/// to that size.
+#[repr(C)]
+pub(crate) struct GspArgumentsAligned {
+    pub(crate) inner: GspArgumentsCached,
+    _padding: [u8; GSP_PAGE_SIZE - core::mem::size_of::<bindings::GSP_ARGUMENTS_CACHED>()],
+}
+
+// SAFETY: Padding is explicit and will not contain uninitialized data.
+unsafe impl AsBytes for GspArgumentsAligned {}
+
 // SAFETY: This struct only contains integer types for which all bit patterns
 // are valid.
-unsafe impl FromBytes for GspArgumentsCached {}
+unsafe impl FromBytes for GspArgumentsAligned {}

 /// Init arguments for the message queue.
 #[repr(transparent)]