On Fri, Jan 29, 2021 at 03:43:40PM +0800, Jason Wang wrote:
On 2021/1/28 下午10:41, Stefano Garzarella wrote:
Usually iotlb accesses are synchronized with a spinlock.
Let's request it as a new parameter in vringh_set_iotlb() and
hold it when we navigate the iotlb in iotlb_translate() to avoid
race conditions with any new additions/deletions of ranges from
the ioltb.
Patch looks fine but I wonder if this is the best approach comparing
to do locking by the caller.
Initially I tried to hold the lock in the vdpasim_blk_work(), but since
we have a lot of different functions for vringh, I opted to take the
lock at the beginning and release it at the end.
Also because several times I went to see if that call used
iotlb_translate or not.
This could be a problem for example if we have multiple workers to
handle multiple queues.
Also, some functions are quite long (e.g. vringh_getdesc_iotlb) and
holding the lock for that long could reduce parallelism.
For these reasons I thought it was better to hide everything from the
caller who doesn't have to worry about which function calls
iotlb_translate() and thus hold the lock.
Thanks,
Stefano
Thanks
Signed-off-by: Stefano Garzarella <sgarzare@xxxxxxxxxx>
---
include/linux/vringh.h | 6 +++++-
drivers/vdpa/vdpa_sim/vdpa_sim.c | 3 ++-
drivers/vhost/vringh.c | 9 ++++++++-
3 files changed, 15 insertions(+), 3 deletions(-)
diff --git a/include/linux/vringh.h b/include/linux/vringh.h
index 59bd50f99291..9c077863c8f6 100644
--- a/include/linux/vringh.h
+++ b/include/linux/vringh.h
@@ -46,6 +46,9 @@ struct vringh {
/* IOTLB for this vring */
struct vhost_iotlb *iotlb;
+ /* spinlock to synchronize IOTLB accesses */
+ spinlock_t *iotlb_lock;
+
/* The function to call to notify the guest about added buffers */
void (*notify)(struct vringh *);
};
@@ -258,7 +261,8 @@ static inline __virtio64 cpu_to_vringh64(const struct vringh *vrh, u64 val)
#if IS_REACHABLE(CONFIG_VHOST_IOTLB)
-void vringh_set_iotlb(struct vringh *vrh, struct vhost_iotlb *iotlb);
+void vringh_set_iotlb(struct vringh *vrh, struct vhost_iotlb *iotlb,
+ spinlock_t *iotlb_lock);
int vringh_init_iotlb(struct vringh *vrh, u64 features,
unsigned int num, bool weak_barriers,
diff --git a/drivers/vdpa/vdpa_sim/vdpa_sim.c b/drivers/vdpa/vdpa_sim/vdpa_sim.c
index 2183a833fcf4..53238989713d 100644
--- a/drivers/vdpa/vdpa_sim/vdpa_sim.c
+++ b/drivers/vdpa/vdpa_sim/vdpa_sim.c
@@ -284,7 +284,8 @@ struct vdpasim *vdpasim_create(struct vdpasim_dev_attr *dev_attr)
goto err_iommu;
for (i = 0; i < dev_attr->nvqs; i++)
- vringh_set_iotlb(&vdpasim->vqs[i].vring, vdpasim->iommu);
+ vringh_set_iotlb(&vdpasim->vqs[i].vring, vdpasim->iommu,
+ &vdpasim->iommu_lock);
ret = iova_cache_get();
if (ret)
diff --git a/drivers/vhost/vringh.c b/drivers/vhost/vringh.c
index 85d85faba058..f68122705719 100644
--- a/drivers/vhost/vringh.c
+++ b/drivers/vhost/vringh.c
@@ -1074,6 +1074,8 @@ static int iotlb_translate(const struct vringh *vrh,
int ret = 0;
u64 s = 0;
+ spin_lock(vrh->iotlb_lock);
+
while (len > s) {
u64 size, pa, pfn;
@@ -1103,6 +1105,8 @@ static int iotlb_translate(const struct vringh *vrh,
++ret;
}
+ spin_unlock(vrh->iotlb_lock);
+
return ret;
}
@@ -1262,10 +1266,13 @@ EXPORT_SYMBOL(vringh_init_iotlb);
* vringh_set_iotlb - initialize a vringh for a ring with IOTLB.
* @vrh: the vring
* @iotlb: iotlb associated with this vring
+ * @iotlb_lock: spinlock to synchronize the iotlb accesses
*/
-void vringh_set_iotlb(struct vringh *vrh, struct vhost_iotlb *iotlb)
+void vringh_set_iotlb(struct vringh *vrh, struct vhost_iotlb *iotlb,
+ spinlock_t *iotlb_lock)
{
vrh->iotlb = iotlb;
+ vrh->iotlb_lock = iotlb_lock;
}
EXPORT_SYMBOL(vringh_set_iotlb);
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