[PATCH v5 1/7] vfio/nvgrace-gpu: Use faults to map device memory

ankita
2025-11-24T11:59:40Z

From: Ankit Agrawal <ankita@nvidia.com>

To make use of the huge pfnmap support and to support zap/remap
sequence, fault/huge_fault ops based mapping mechanism needs to
be implemented.

Currently nvgrace-gpu module relies on remap_pfn_range to do
the mapping during VM bootup. Replace it to instead rely on fault
and use vmf_insert_pfn to setup the mapping.

Signed-off-by: Ankit Agrawal <ankita@nvidia.com>
---
drivers/vfio/pci/nvgrace-gpu/main.c | 50 +++++++++++++++++------------
1 file changed, 30 insertions(+), 20 deletions(-)

diff --git a/drivers/vfio/pci/nvgrace-gpu/main.c b/drivers/vfio/pci/nvgrace-gpu/main.c
index e346392b72f6..f74f3d8e1ebe 100644
--- a/drivers/vfio/pci/nvgrace-gpu/main.c
+++ b/drivers/vfio/pci/nvgrace-gpu/main.c
@@ -130,6 +130,32 @@ static void nvgrace_gpu_close_device(struct vfio_device *core_vdev)
vfio_pci_core_close_device(core_vdev);
}

+static vm_fault_t nvgrace_gpu_vfio_pci_fault(struct vm_fault *vmf)
+{
+ struct vm_area_struct *vma = vmf->vma;
+ struct nvgrace_gpu_pci_core_device *nvdev = vma->vm_private_data;
+ int index = vma->vm_pgoff >> (VFIO_PCI_OFFSET_SHIFT - PAGE_SHIFT);
+ vm_fault_t ret = VM_FAULT_SIGBUS;
+ struct mem_region *memregion;
+ unsigned long pgoff, pfn;
+
+ memregion = nvgrace_gpu_memregion(index, nvdev);
+ if (!memregion)
+ return ret;
+
+ pgoff = (vmf->address - vma->vm_start) >> PAGE_SHIFT;
+ pfn = PHYS_PFN(memregion->memphys) + pgoff;
+
+ scoped_guard(rwsem_read, &nvdev->core_device.memory_lock)
+ ret = vmf_insert_pfn(vmf->vma, vmf->address, pfn);
+
+ return ret;
+}
+
+static const struct vm_operations_struct nvgrace_gpu_vfio_pci_mmap_ops = {
+ .fault = nvgrace_gpu_vfio_pci_fault,
+};
+
static int nvgrace_gpu_mmap(struct vfio_device *core_vdev,
struct vm_area_struct *vma)
{
@@ -137,10 +163,8 @@ static int nvgrace_gpu_mmap(struct vfio_device *core_vdev,
container_of(core_vdev, struct nvgrace_gpu_pci_core_device,
core_device.vdev);
struct mem_region *memregion;
- unsigned long start_pfn;
u64 req_len, pgoff, end;
unsigned int index;
- int ret = 0;

index = vma->vm_pgoff >> (VFIO_PCI_OFFSET_SHIFT - PAGE_SHIFT);

@@ -157,7 +181,6 @@ static int nvgrace_gpu_mmap(struct vfio_device *core_vdev,
((1U << (VFIO_PCI_OFFSET_SHIFT - PAGE_SHIFT)) - 1);

if (check_sub_overflow(vma->vm_end, vma->vm_start, &req_len) ||
- check_add_overflow(PHYS_PFN(memregion->memphys), pgoff, &start_pfn) ||
check_add_overflow(PFN_PHYS(pgoff), req_len, &end))
return -EOVERFLOW;

@@ -168,6 +191,8 @@ static int nvgrace_gpu_mmap(struct vfio_device *core_vdev,
if (end > memregion->memlength)
return -EINVAL;

+ vm_flags_set(vma, VM_IO | VM_PFNMAP | VM_DONTEXPAND | VM_DONTDUMP);
+
/*
* The carved out region of the device memory needs the NORMAL_NC
* property. Communicate as such to the hypervisor.
@@ -184,23 +209,8 @@ static int nvgrace_gpu_mmap(struct vfio_device *core_vdev,
vma->vm_page_prot = pgprot_writecombine(vma->vm_page_prot);
}

- /*
- * Perform a PFN map to the memory and back the device BAR by the
- * GPU memory.
- *
- * The available GPU memory size may not be power-of-2 aligned. The
- * remainder is only backed by vfio_device_ops read/write handlers.
- *
- * During device reset, the GPU is safely disconnected to the CPU
- * and access to the BAR will be immediately returned preventing
- * machine check.
- */
- ret = remap_pfn_range(vma, vma->vm_start, start_pfn,
- req_len, vma->vm_page_prot);
- if (ret)
- return ret;
-
- vma->vm_pgoff = start_pfn;
+ vma->vm_ops = &nvgrace_gpu_vfio_pci_mmap_ops;
+ vma->vm_private_data = nvdev;

return 0;
}
--
2.34.1