[PATCH v2 5/8] vfio: Change vfio_external_check_extension() to vfio_file_enforced_coherent()

Jason Gunthorpe
2022-04-20T19:23:26Z

Instead of a general extension check change the function into a limited
test if the iommu_domain has enforced coherency, which is the only thing
kvm needs to query.

Make the new op self contained by properly refcounting the container
before touching it.

Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>
---
drivers/vfio/vfio.c | 30 +++++++++++++++++++++++++++---
include/linux/vfio.h | 3 +--
virt/kvm/vfio.c | 16 ++++++++--------
3 files changed, 36 insertions(+), 13 deletions(-)

diff --git a/drivers/vfio/vfio.c b/drivers/vfio/vfio.c
index c9122c84583aa1..ae3e802991edf2 100644
--- a/drivers/vfio/vfio.c
+++ b/drivers/vfio/vfio.c
@@ -2005,11 +2005,35 @@ struct iommu_group *vfio_file_iommu_group(struct file *file)
}
EXPORT_SYMBOL_GPL(vfio_file_iommu_group);

-long vfio_external_check_extension(struct vfio_group *group, unsigned long arg)
+/**
+ * vfio_file_enforced_coherent - True if the DMA associated with the VFIO file
+ * is always CPU cache coherent
+ * @file: VFIO group file
+ *
+ * Enforced coherency means that the IOMMU ignores things like the PCIe no-snoop
+ * bit in DMA transactions. A return of false indicates that the user has
+ * rights to access additional instructions such as wbinvd on x86.
+ */
+bool vfio_file_enforced_coherent(struct file *file)
{
- return vfio_ioctl_check_extension(group->container, arg);
+ struct vfio_group *group = file->private_data;
+ bool ret;
+
+ if (file->f_op != &vfio_group_fops)
+ return true;
+
+ /*
+ * Since the coherency state is determined only once a container is
+ * attached the user must do so before they can prove they have
+ * permission.
+ */
+ if (vfio_group_add_container_user(group))
+ return true;
+ ret = vfio_ioctl_check_extension(group->container, VFIO_DMA_CC_IOMMU);
+ vfio_group_try_dissolve_container(group);
+ return ret;
}
-EXPORT_SYMBOL_GPL(vfio_external_check_extension);
+EXPORT_SYMBOL_GPL(vfio_file_enforced_coherent);

/*
* Sub-module support
diff --git a/include/linux/vfio.h b/include/linux/vfio.h
index 132cf3e7cda8db..7f022ae126a392 100644
--- a/include/linux/vfio.h
+++ b/include/linux/vfio.h
@@ -143,8 +143,7 @@ extern void vfio_group_put_external_user(struct vfio_group *group);
extern struct vfio_group *vfio_group_get_external_user_from_dev(struct device
*dev);
extern struct iommu_group *vfio_file_iommu_group(struct file *file);
-extern long vfio_external_check_extension(struct vfio_group *group,
- unsigned long arg);
+extern bool vfio_file_enforced_coherent(struct file *file);

#define VFIO_PIN_PAGES_MAX_ENTRIES (PAGE_SIZE/sizeof(unsigned long))

diff --git a/virt/kvm/vfio.c b/virt/kvm/vfio.c
index 50193ae270faca..2330b0c272e671 100644
--- a/virt/kvm/vfio.c
+++ b/virt/kvm/vfio.c
@@ -75,20 +75,20 @@ static void kvm_vfio_group_set_kvm(struct vfio_group *group, struct kvm *kvm)
symbol_put(vfio_group_set_kvm);
}

-static bool kvm_vfio_group_is_coherent(struct vfio_group *vfio_group)
+static bool kvm_vfio_file_enforced_coherent(struct file *file)
{
- long (*fn)(struct vfio_group *, unsigned long);
- long ret;
+ bool (*fn)(struct file *file);
+ bool ret;

- fn = symbol_get(vfio_external_check_extension);
+ fn = symbol_get(vfio_file_enforced_coherent);
if (!fn)
return false;

- ret = fn(vfio_group, VFIO_DMA_CC_IOMMU);
+ ret = fn(file);

- symbol_put(vfio_external_check_extension);
+ symbol_put(vfio_file_enforced_coherent);

- return ret > 0;
+ return ret;
}

#ifdef CONFIG_SPAPR_TCE_IOMMU
@@ -136,7 +136,7 @@ static void kvm_vfio_update_coherency(struct kvm_device *dev)
mutex_lock(&kv->lock);

list_for_each_entry(kvg, &kv->group_list, node) {
- if (!kvm_vfio_group_is_coherent(kvg->vfio_group)) {
+ if (!kvm_vfio_file_enforced_coherent(kvg->file)) {
noncoherent = true;
break;
}
--
2.36.0