Hi,
On 02/06/2023 01:48, Vikram Garhwal wrote:
Dynamic programming ops will modify the dt_host and there might be other
function which are browsing the dt_host at the same time. To avoid the race
conditions, adding rwlock for browsing the dt_host during runtime.
Please explain that writer will be added in a follow-up patch.
Reason behind adding rwlock instead of spinlock:
For now, dynamic programming is the sole modifier of dt_host in Xen during
run time. All other access functions like iommu_release_dt_device() are
just reading the dt_host during run-time. So, there is a need to
protect
others from browsing the dt_host while dynamic programming is modifying
it. rwlock is better suitable for this task as spinlock won't be able
to
differentiate between read and write access.
Signed-off-by: Vikram Garhwal <vikram.garh...@amd.com>
---
Changes from v6:
Remove redundant "read_unlock(&dt_host->lock);" in the following case:
XEN_DOMCTL_deassign_device
---
xen/common/device_tree.c | 4 ++++
xen/drivers/passthrough/device_tree.c | 15 +++++++++++++++
xen/include/xen/device_tree.h | 6 ++++++
3 files changed, 25 insertions(+)
diff --git a/xen/common/device_tree.c b/xen/common/device_tree.c
index c5250a1644..c8fcdf8fa1 100644
--- a/xen/common/device_tree.c
+++ b/xen/common/device_tree.c
@@ -2146,7 +2146,11 @@ int unflatten_device_tree(const void *fdt, struct
dt_device_node **mynodes)
dt_dprintk(" <- unflatten_device_tree()\n");
+ /* Init r/w lock for host device tree. */
+ rwlock_init(&dt_host->lock);
+
return 0;
+
}
static void dt_alias_add(struct dt_alias_prop *ap,
diff --git a/xen/drivers/passthrough/device_tree.c
b/xen/drivers/passthrough/device_tree.c
index 301a5bcd97..f4d9deb624 100644
--- a/xen/drivers/passthrough/device_tree.c
+++ b/xen/drivers/passthrough/device_tree.c
@@ -112,6 +112,8 @@ int iommu_release_dt_devices(struct domain *d)
if ( !is_iommu_enabled(d) )
return 0;
+ read_lock(&dt_host->lock);
+
list_for_each_entry_safe(dev, _dev, &hd->dt_devices, domain_list)
{
rc = iommu_deassign_dt_device(d, dev);
@@ -119,10 +121,14 @@ int iommu_release_dt_devices(struct domain *d)
{
dprintk(XENLOG_ERR, "Failed to deassign %s in domain %u\n",
dt_node_full_name(dev), d->domain_id);
+
+ read_unlock(&dt_host->lock);
return rc;
}
}
+ read_unlock(&dt_host->lock);
+
return 0;
}
@@ -246,6 +252,8 @@ int iommu_do_dt_domctl(struct xen_domctl *domctl, struct domain *d,
int ret;
struct dt_device_node *dev;
+ read_lock(&dt_host->lock);
+
switch ( domctl->cmd )
{
case XEN_DOMCTL_assign_device:
@@ -295,7 +303,10 @@ int iommu_do_dt_domctl(struct xen_domctl *domctl, struct
domain *d,
spin_unlock(&dtdevs_lock);
if ( d == dom_io )
+ {
+ read_unlock(&dt_host->lock);
return -EINVAL;
+ }
ret = iommu_add_dt_device(dev);
if ( ret < 0 )
@@ -333,7 +344,10 @@ int iommu_do_dt_domctl(struct xen_domctl *domctl, struct
domain *d,
break;
if ( d == dom_io )
+ {
+ read_unlock(&dt_host->lock);
return -EINVAL;
+ }
ret = iommu_deassign_dt_device(d, dev);
@@ -348,5 +362,6 @@ int iommu_do_dt_domctl(struct xen_domctl *domctl, struct domain *d,
break;
}
+ read_unlock(&dt_host->lock);
return ret;
}
diff --git a/xen/include/xen/device_tree.h b/xen/include/xen/device_tree.h
index e239f7de26..dee40d2ea3 100644
--- a/xen/include/xen/device_tree.h
+++ b/xen/include/xen/device_tree.h
@@ -18,6 +18,7 @@
#include <xen/string.h>
#include <xen/types.h>
#include <xen/list.h>
+#include <xen/rwlock.h>
#define DEVICE_TREE_MAX_DEPTH 16
@@ -106,6 +107,11 @@ struct dt_device_node {
struct list_head domain_list;
struct device dev;
+
+ /*
+ * Lock that protects r/w updates to unflattened device tree i.e. dt_host.
+ */
From the description, it sounds like the rwlock will only be used to
protect the entire device-tree rather than a single node. So it doesn't
seem to be sensible to increase each node structure (there are a lot) by
12 bytes.
Can you outline your plan?
+ rwlock_t lock;
};
#define dt_to_dev(dt_node) (&(dt_node)->dev)
Cheers,
--
Julien Grall
