linux-kernel - [PATCH v4 20/22] vfio_pci: Allow to mmap the fault queue

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Date:   Mon, 18 Feb 2019 14:55:01 +0100
From:   Eric Auger <eric.auger@...hat.com>
To:     eric.auger.pro@...il.com, eric.auger@...hat.com,
        iommu@...ts.linux-foundation.org, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org, kvmarm@...ts.cs.columbia.edu, joro@...tes.org,
        alex.williamson@...hat.com, jacob.jun.pan@...ux.intel.com,
        yi.l.liu@...ux.intel.com, jean-philippe.brucker@....com,
        will.deacon@....com, robin.murphy@....com
Cc:     kevin.tian@...el.com, ashok.raj@...el.com, marc.zyngier@....com,
        christoffer.dall@....com, peter.maydell@...aro.org
Subject: [PATCH v4 20/22] vfio_pci: Allow to mmap the fault queue

The Producer Fault region contains the fault queue in the second page.
There is benefit to let the userspace mmap this area. So let's expose
this mmappable area through a sparse mmap entry and implement the mmap
operation.

Signed-off-by: Eric Auger <eric.auger@...hat.com>
---
 drivers/vfio/pci/vfio_pci.c | 61 +++++++++++++++++++++++++++++++++++--
 1 file changed, 59 insertions(+), 2 deletions(-)

diff --git a/drivers/vfio/pci/vfio_pci.c b/drivers/vfio/pci/vfio_pci.c
index 019c9fd380a5..3aaa14eb5518 100644
--- a/drivers/vfio/pci/vfio_pci.c
+++ b/drivers/vfio/pci/vfio_pci.c
@@ -223,15 +223,70 @@ static const struct vfio_pci_fault_abi fault_abi_versions[] = {
 
 #define NR_FAULT_ABIS ARRAY_SIZE(fault_abi_versions)
 
+static int vfio_pci_fault_mmap(struct vfio_pci_device *vdev,
+			       struct vfio_pci_region *region,
+			       struct vm_area_struct *vma)
+{
+	u64 phys_len, req_len, pgoff, req_start;
+	unsigned long long addr;
+	unsigned int index, ret;
+
+	index = vma->vm_pgoff >> (VFIO_PCI_OFFSET_SHIFT - PAGE_SHIFT);
+
+	phys_len = region->size;
+
+	req_len = vma->vm_end - vma->vm_start;
+	pgoff = vma->vm_pgoff &
+		((1U << (VFIO_PCI_OFFSET_SHIFT - PAGE_SHIFT)) - 1);
+	req_start = pgoff << PAGE_SHIFT;
+
+	/* only the second page of the producer fault region is mmappable */
+	if (req_start < PAGE_SIZE)
+		return -EINVAL;
+
+	if (req_start + req_len > phys_len)
+		return -EINVAL;
+
+	addr = virt_to_phys(vdev->fault_pages);
+	vma->vm_private_data = vdev;
+	vma->vm_pgoff = (addr >> PAGE_SHIFT) + pgoff;
+
+	ret = remap_pfn_range(vma, vma->vm_start, vma->vm_pgoff,
+			      req_len, vma->vm_page_prot);
+	return ret;
+}
+
 static int vfio_pci_fault_prod_add_capability(struct vfio_pci_device *vdev,
 		struct vfio_pci_region *region, struct vfio_info_cap *caps)
 {
+	struct vfio_region_info_cap_sparse_mmap *sparse = NULL;
 	struct vfio_region_info_cap_fault cap = {
 		.header.id = VFIO_REGION_INFO_CAP_PRODUCER_FAULT,
 		.header.version = 1,
 		.version = NR_FAULT_ABIS,
 	};
-	return vfio_info_add_capability(caps, &cap.header, sizeof(cap));
+	size_t size = sizeof(*sparse) + sizeof(*sparse->areas);
+	int ret;
+
+	ret = vfio_info_add_capability(caps, &cap.header, sizeof(cap));
+	if (ret)
+		return ret;
+
+	sparse = kzalloc(size, GFP_KERNEL);
+	if (!sparse)
+		return -ENOMEM;
+
+	sparse->header.id = VFIO_REGION_INFO_CAP_SPARSE_MMAP;
+	sparse->header.version = 1;
+	sparse->nr_areas = 1;
+	sparse->areas[0].offset = PAGE_SIZE;
+	sparse->areas[0].size = PAGE_SIZE;
+
+	ret = vfio_info_add_capability(caps, &sparse->header, size);
+	if (ret)
+		kfree(sparse);
+
+	return ret;
 }
 
 static const struct vfio_pci_regops vfio_pci_fault_cons_regops = {
@@ -242,6 +297,7 @@ static const struct vfio_pci_regops vfio_pci_fault_cons_regops = {
 static const struct vfio_pci_regops vfio_pci_fault_prod_regops = {
 	.rw		= vfio_pci_fault_prod_rw,
 	.release	= vfio_pci_fault_release,
+	.mmap		= vfio_pci_fault_mmap,
 	.add_capability = vfio_pci_fault_prod_add_capability,
 };
 
@@ -300,7 +356,8 @@ static int vfio_pci_init_fault_region(struct vfio_pci_device *vdev)
 		VFIO_REGION_TYPE_NESTED,
 		VFIO_REGION_SUBTYPE_NESTED_FAULT_PROD,
 		&vfio_pci_fault_prod_regops, 2 * PAGE_SIZE,
-		VFIO_REGION_INFO_FLAG_READ, vdev->fault_pages);
+		VFIO_REGION_INFO_FLAG_READ | VFIO_REGION_INFO_FLAG_MMAP,
+		vdev->fault_pages);
 	if (ret)
 		goto out;
 
-- 
2.20.1