[PATCH 0/1] vhost, use_mm and KERNEL_DS

[PATCH 0/1] vhost, use_mm and KERNEL_DS

[Christian Borntraeger]

Folks,

here is a patch that fixes vhost to use USER_DS before
doing a use_mm/usercopy operation. This was found during
vhost prototyping on s390 were we have a separate user/kernel
address space.


Jens Freimann (1):
  use USER_DS in vhost_worker thread

 drivers/vhost/vhost.c |    3 +++
 1 files changed, 3 insertions(+), 0 deletions(-)

[PATCH 1/1] use USER_DS in vhost_worker thread

[Christian Borntraeger]

From: Jens Freimann <jfrei@linux.vnet.ibm.com>

On some architectures address spaces are set up in a way that this is
not necessary to work properly but on some others (like s390) it is.
Make sure we operate on the user address space to allow copy_xxx_user()
from the vhost_worker() thread by setting it explicitly before calling
use_mm() and revert it after unuse_mm().

Signed-off-by: Jens Freimann <jfrei@linux.vnet.ibm.com>
Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>
---
 drivers/vhost/vhost.c |    3 +++
 1 files changed, 3 insertions(+), 0 deletions(-)

diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
index 94dbd25..112156f 100644
--- a/drivers/vhost/vhost.c
+++ b/drivers/vhost/vhost.c
@@ -191,7 +191,9 @@ static int vhost_worker(void *data)
 	struct vhost_dev *dev = data;
 	struct vhost_work *work = NULL;
 	unsigned uninitialized_var(seq);
+	mm_segment_t oldfs = get_fs();
 
+	set_fs(USER_DS);
 	use_mm(dev->mm);
 
 	for (;;) {
@@ -229,6 +231,7 @@ static int vhost_worker(void *data)
 
 	}
 	unuse_mm(dev->mm);
+	set_fs(oldfs);
 	return 0;
 }
 
-- 
1.7.0.4

Re: [PATCH 1/1] use USER_DS in vhost_worker thread

[Michael S. Tsirkin]

On Tue, Jun 26, 2012 at 12:59:58PM +0200, Christian Borntraeger wrote:
> From: Jens Freimann <jfrei@linux.vnet.ibm.com>
> 
> On some architectures address spaces are set up in a way that this is
> not necessary to work properly but on some others (like s390) it is.
> Make sure we operate on the user address space to allow copy_xxx_user()
> from the vhost_worker() thread by setting it explicitly before calling
> use_mm() and revert it after unuse_mm().
> 
> Signed-off-by: Jens Freimann <jfrei@linux.vnet.ibm.com>
> Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>

Acked-by: Michael S. Tsirkin <mst@redhat.com>

Dave, can you queue this up for 3.5 please?

Thanks.

> ---
>  drivers/vhost/vhost.c |    3 +++
>  1 files changed, 3 insertions(+), 0 deletions(-)
> 
> diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
> index 94dbd25..112156f 100644
> --- a/drivers/vhost/vhost.c
> +++ b/drivers/vhost/vhost.c
> @@ -191,7 +191,9 @@ static int vhost_worker(void *data)
>  	struct vhost_dev *dev = data;
>  	struct vhost_work *work = NULL;
>  	unsigned uninitialized_var(seq);
> +	mm_segment_t oldfs = get_fs();
>  
> +	set_fs(USER_DS);
>  	use_mm(dev->mm);
>  
>  	for (;;) {
> @@ -229,6 +231,7 @@ static int vhost_worker(void *data)
>  
>  	}
>  	unuse_mm(dev->mm);
> +	set_fs(oldfs);
>  	return 0;
>  }
>  
> -- 
> 1.7.0.4