From: Manish Honap <[email protected]> A CXL Type-2 guest maps the device HDM memory to use its coherent CXL.mem. The HDM memory is a host physical range with no struct page, so the guest and KVM need a write-back mapping of it.
Register the range as an mmap-able region under VFIO_REGION_TYPE_PCI_VENDOR_TYPE with the CXL vendor id rather than a bespoke region type, per open because vfio_pci_core_disable() tears down all dynamic regions on close. Own the resolved host physical range exclusively (IORESOURCE_EXCLUSIVE) so nothing, /dev/mem included, can map a conflicting cacheable alias that would fault the host once the range is mapped write-back. There is no devm form of the exclusive request, so pair it with a devm release action. vfio_pci_zap_bars() only unmaps the fixed PCI BAR range, so revoke mmap-capable device-specific regions there too. Otherwise a Memory-Space disable, a D3 transition, or a reset would leave the guest a live mapping into quiesced device memory; the fault handler re-gates on device state before it inserts a pfn again. Assisted-by: LLM Signed-off-by: Manish Honap <[email protected]> --- drivers/vfio/pci/cxl/vfio_cxl_core.c | 186 +++++++++++++++++++++++++++ drivers/vfio/pci/vfio_pci_core.c | 37 ++++++ include/linux/vfio_pci_core.h | 1 + include/uapi/linux/vfio.h | 4 + 4 files changed, 228 insertions(+) diff --git a/drivers/vfio/pci/cxl/vfio_cxl_core.c b/drivers/vfio/pci/cxl/vfio_cxl_core.c index 5c8a63833a43..5b65cac30aba 100644 --- a/drivers/vfio/pci/cxl/vfio_cxl_core.c +++ b/drivers/vfio/pci/cxl/vfio_cxl_core.c @@ -5,9 +5,13 @@ * Copyright (c) 2026 NVIDIA Corporation & Affiliates */ +#include <linux/cleanup.h> +#include <linux/io.h> +#include <linux/mm.h> #include <linux/module.h> #include <linux/pci.h> #include <linux/range.h> +#include <linux/uaccess.h> #include <linux/vfio_pci_core.h> #include <cxl/cxl.h> #include <cxl/pci.h> @@ -17,13 +21,144 @@ * @cxlds: CXL device state; kept first for devm_cxl_dev_state_create() * @cxlmd: memory device joined to the CXL topology at bind * @hpa_range: host physical range of the HDM region + * @hdm_valid: true when host CPU access to the HDM range is safe; under memory_lock */ struct vfio_cxl_state { struct cxl_dev_state cxlds; struct cxl_memdev *cxlmd; struct range hpa_range; + bool hdm_valid; }; +static unsigned long vfio_cxl_mem_pgoff(struct vm_area_struct *vma, + unsigned long addr) +{ + unsigned long mask = (1U << (VFIO_PCI_OFFSET_SHIFT - PAGE_SHIFT)) - 1; + + return (vma->vm_pgoff & mask) + ((addr - vma->vm_start) >> PAGE_SHIFT); +} + +static vm_fault_t vfio_cxl_mem_huge_fault(struct vm_fault *vmf, + unsigned int order) +{ + struct vm_area_struct *vma = vmf->vma; + struct vfio_pci_core_device *vdev = vma->vm_private_data; + struct vfio_cxl_state *cxl = vdev->cxl; + unsigned long addr = ALIGN_DOWN(vmf->address, PAGE_SIZE << order); + unsigned long pfn = PHYS_PFN(cxl->hpa_range.start) + + vfio_cxl_mem_pgoff(vma, addr); + vm_fault_t ret = VM_FAULT_FALLBACK; + + if (is_aligned_for_order(vma, addr, pfn, order)) { + scoped_guard(rwsem_read, &vdev->memory_lock) { + /* + * Insert a PFN only for a known-good decoder whose + * media is ready and whose Memory-Space is enabled. + */ + if (__vfio_pci_memory_enabled(vdev) && + cxl->hdm_valid && cxl->cxlds.media_ready) + ret = vfio_pci_vmf_insert_pfn(vdev, vmf, pfn, + order); + else + ret = VM_FAULT_SIGBUS; + } + } + + return ret; +} + +static vm_fault_t vfio_cxl_mem_fault(struct vm_fault *vmf) +{ + return vfio_cxl_mem_huge_fault(vmf, 0); +} + +static const struct vm_operations_struct vfio_cxl_mem_vm_ops = { + .fault = vfio_cxl_mem_fault, +#ifdef CONFIG_ARCH_SUPPORTS_HUGE_PFNMAP + .huge_fault = vfio_cxl_mem_huge_fault, +#endif +}; + +static int vfio_cxl_mem_mmap(struct vfio_pci_core_device *vdev, + struct vfio_pci_region *region, + struct vm_area_struct *vma) +{ + unsigned long mask = (1U << (VFIO_PCI_OFFSET_SHIFT - PAGE_SHIFT)) - 1; + u64 req_start = (vma->vm_pgoff & mask) << PAGE_SHIFT; + u64 req_len = vma->vm_end - vma->vm_start; + + if (req_start + req_len > region->size) + return -EINVAL; + + /* + * CXL.mem is coherent memory, so leave the mapping write-back cacheable. + */ + vm_flags_set(vma, VM_IO | VM_PFNMAP | VM_DONTEXPAND | VM_DONTDUMP); + vma->vm_ops = &vfio_cxl_mem_vm_ops; + vma->vm_private_data = vdev; + + return 0; +} + +static ssize_t vfio_cxl_mem_rw(struct vfio_pci_core_device *vdev, + char __user *buf, size_t count, loff_t *ppos, + bool iswrite) +{ + struct vfio_cxl_state *cxl = vdev->cxl; + u64 pos = *ppos & VFIO_PCI_OFFSET_MASK; + void *mem; + ssize_t done; + + if (pos >= range_len(&cxl->hpa_range)) + return -EINVAL; + count = min_t(size_t, count, range_len(&cxl->hpa_range) - pos); + + scoped_guard(rwsem_read, &vdev->memory_lock) { + /* + * Same gate as the fault path: only touch the HDM range with + * the decoder in a known-good state AND Memory-Space enabled, + * or a host CPU access aborts as a fatal SError. + */ + if (!cxl->hdm_valid || !__vfio_pci_memory_enabled(vdev)) + return -EIO; + + mem = memremap(cxl->hpa_range.start + pos, count, MEMREMAP_WB); + if (!mem) + return -ENOMEM; + if (iswrite) + done = copy_from_user(mem, buf, count) ? -EFAULT : count; + else + done = copy_to_user(buf, mem, count) ? -EFAULT : count; + memunmap(mem); + } + if (done > 0) + *ppos += done; + + return done; +} + +/* + * The CXL regions carry no per-region state (region->data is the shared, + * devm-managed vfio_cxl_state), so releasing a region is a no-op. + */ +static void vfio_cxl_region_release(struct vfio_pci_core_device *vdev, + struct vfio_pci_region *region) +{ +} + +static const struct vfio_pci_regops vfio_cxl_mem_regops = { + .rw = vfio_cxl_mem_rw, + .mmap = vfio_cxl_mem_mmap, + .release = vfio_cxl_region_release, +}; + +static void vfio_cxl_release_hpa(void *data) +{ + struct vfio_cxl_state *cxl = data; + + release_mem_region(cxl->hpa_range.start, range_len(&cxl->hpa_range)); +} + static int vfio_cxl_init_device(struct vfio_pci_core_device *vdev) { struct pci_dev *pdev = vdev->pdev; @@ -120,6 +255,21 @@ static int vfio_cxl_init_device(struct vfio_pci_core_device *vdev) goto err; } + /* + * Claim the range IORESOURCE_EXCLUSIVE so no conflicting cacheable + * alias can fault the host once it is mapped write-back; there is no + * devm form, so pair it with a devm release action. + */ + if (!request_mem_region_exclusive(cxl->hpa_range.start, + range_len(&cxl->hpa_range), + "vfio-cxl-hdm")) { + ret = -EBUSY; + goto err; + } + ret = devm_add_action_or_reset(&pdev->dev, vfio_cxl_release_hpa, cxl); + if (ret) + goto err; + cxl->cxlmd = cxlmd; devres_close_group(&pdev->dev, NULL); @@ -143,13 +293,49 @@ static void vfio_cxl_release_device(struct vfio_pci_core_device *vdev) vdev->cxl = NULL; } +static int vfio_cxl_add_region(struct vfio_pci_core_device *vdev, u32 subtype, + const struct vfio_pci_regops *ops, size_t size, + u32 flags) +{ + u32 type = VFIO_REGION_TYPE_PCI_VENDOR_TYPE | PCI_VENDOR_ID_CXL; + + return vfio_pci_core_register_dev_region(vdev, type, subtype, ops, + size, flags, vdev->cxl); +} + static int vfio_cxl_open_device(struct vfio_pci_core_device *vdev) { + struct vfio_cxl_state *cxl = vdev->cxl; + int ret; + + /* + * vfio_pci_core_disable() frees all dynamic regions on close, so register + * them here per open rather than at bind. A failed first open never + * reaches close_device(), so unwind on error. + */ + ret = vfio_cxl_add_region(vdev, VFIO_REGION_SUBTYPE_CXL_MEM, + &vfio_cxl_mem_regops, range_len(&cxl->hpa_range), + VFIO_REGION_INFO_FLAG_READ | + VFIO_REGION_INFO_FLAG_WRITE | + VFIO_REGION_INFO_FLAG_MMAP); + if (ret) + return ret; + + /* + * The decoder is firmware-committed, so host access to the HDM range is + * safe. Open the access gate; reset and power transitions clear it until + * the decoder is restored. + */ + cxl->hdm_valid = true; + return 0; } static void vfio_cxl_close_device(struct vfio_pci_core_device *vdev) { + struct vfio_cxl_state *cxl = vdev->cxl; + + cxl->hdm_valid = false; } static void vfio_cxl_reset_prepare(struct vfio_pci_core_device *vdev) diff --git a/drivers/vfio/pci/vfio_pci_core.c b/drivers/vfio/pci/vfio_pci_core.c index ddd6807893fd..8913a9e24302 100644 --- a/drivers/vfio/pci/vfio_pci_core.c +++ b/drivers/vfio/pci/vfio_pci_core.c @@ -1295,6 +1295,23 @@ int vfio_pci_core_register_dev_region(struct vfio_pci_core_device *vdev, } EXPORT_SYMBOL_GPL(vfio_pci_core_register_dev_region); +/* + * Unregister the most recently registered dynamic region. Used to unwind a + * partially built region set on an open-time error; regions are otherwise + * released together in vfio_pci_core_disable(). + */ +void vfio_pci_core_unregister_dev_region(struct vfio_pci_core_device *vdev) +{ + struct vfio_pci_region *region; + + if (WARN_ON(!vdev->num_regions)) + return; + + region = &vdev->region[--vdev->num_regions]; + region->ops->release(vdev, region); +} +EXPORT_SYMBOL_GPL(vfio_pci_core_unregister_dev_region); + static int vfio_pci_info_atomic_cap(struct vfio_pci_core_device *vdev, struct vfio_info_cap *caps) { @@ -1972,8 +1989,28 @@ static void vfio_pci_zap_bars(struct vfio_pci_core_device *vdev) loff_t start = VFIO_PCI_INDEX_TO_OFFSET(VFIO_PCI_BAR0_REGION_INDEX); loff_t end = VFIO_PCI_INDEX_TO_OFFSET(VFIO_PCI_ROM_REGION_INDEX); loff_t len = end - start; + unsigned int i; unmap_mapping_range(core_vdev->inode->i_mapping, start, len, true); + + /* + * The unmap above covers the PCI BARs; mmap-capable device-specific + * regions (e.g. a vfio-cxl HDM window) sit above that range, so revoke + * them here too, or a Memory-Space disable, D3/PM transition, or reset + * would leave the guest a live mapping into quiesced device memory. + * Callers hold memory_lock, so the region array is stable. + */ + for (i = 0; i < vdev->num_regions; i++) { + struct vfio_pci_region *region = &vdev->region[i]; + loff_t roff; + + if (!(region->flags & VFIO_REGION_INFO_FLAG_MMAP)) + continue; + + roff = VFIO_PCI_INDEX_TO_OFFSET(VFIO_PCI_NUM_REGIONS + i); + unmap_mapping_range(core_vdev->inode->i_mapping, roff, + region->size, true); + } } void vfio_pci_zap_and_down_write_memory_lock(struct vfio_pci_core_device *vdev) diff --git a/include/linux/vfio_pci_core.h b/include/linux/vfio_pci_core.h index 475a0ecf9e4f..39a28cc6ae8c 100644 --- a/include/linux/vfio_pci_core.h +++ b/include/linux/vfio_pci_core.h @@ -198,6 +198,7 @@ int vfio_pci_core_register_dev_region(struct vfio_pci_core_device *vdev, unsigned int type, unsigned int subtype, const struct vfio_pci_regops *ops, size_t size, u32 flags, void *data); +void vfio_pci_core_unregister_dev_region(struct vfio_pci_core_device *vdev); void vfio_pci_core_close_device(struct vfio_device *core_vdev); int vfio_pci_core_init_dev(struct vfio_device *core_vdev); void vfio_pci_core_release_dev(struct vfio_device *core_vdev); diff --git a/include/uapi/linux/vfio.h b/include/uapi/linux/vfio.h index e41437fa17ad..1bf86763c0f7 100644 --- a/include/uapi/linux/vfio.h +++ b/include/uapi/linux/vfio.h @@ -370,6 +370,10 @@ struct vfio_region_info_cap_type { */ #define VFIO_REGION_SUBTYPE_IBM_NVLINK2_ATSD (1) +/* CXL Type-2 device (0x1e98) sub-types for VFIO_REGION_TYPE_PCI_VENDOR_TYPE */ +/* CXL.mem HDM region of a Type-2 device, mmap-able */ +#define VFIO_REGION_SUBTYPE_CXL_MEM (1) + /* sub-types for VFIO_REGION_TYPE_GFX */ #define VFIO_REGION_SUBTYPE_GFX_EDID (1) -- 2.25.1
