[PATCH net 1/2] tuntap: limit head length of skb allocated

[PATCH net 1/2] tuntap: limit head length of skb allocated

[Jason Wang]

We currently use hdr_len as a hint of head length which is advertised by
guest. But when guest advertise a very big value, it can lead to an 64K+
allocating of kmalloc() which has a very high possibility of failure when host
memory is fragmented or under heavy stress. The huge hdr_len also reduce the
effect of zerocopy or even disable if a gso skb is linearized in guest.

To solves those issues, this patch introduces an upper limit (PAGE_SIZE) of the
head, which guarantees an order 0 allocation each time.

Cc: Stefan Hajnoczi <stefanha@redhat.com>
Cc: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Jason Wang <jasowang@redhat.com>
---
The patch was needed for stable.
---
 drivers/net/tun.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/drivers/net/tun.c b/drivers/net/tun.c
index 7cb105c..5537b65 100644
--- a/drivers/net/tun.c
+++ b/drivers/net/tun.c
@@ -954,6 +954,11 @@ static struct sk_buff *tun_alloc_skb(struct tun_file *tfile,
 	struct sock *sk = tfile->socket.sk;
 	struct sk_buff *skb;
 	int err;
+	int good_linear = SKB_MAX_HEAD(prepad);
+
+	/* Don't use huge linear part */
+	if (linear > good_linear)
+		linear = good_linear;
 
 	/* Under a page?  Don't bother with paged skb. */
 	if (prepad + len < PAGE_SIZE || !linear)
-- 
1.8.3.2

[PATCH net 2/2] macvtap: limit head length of skb allocated

[Jason Wang]

We currently use hdr_len as a hint of head length which is advertised by
guest. But when guest advertise a very big value, it can lead to an 64K+
allocating of kmalloc() which has a very high possibility of failure when host
memory is fragmented or under heavy stress. The huge hdr_len also reduce the
effect of zerocopy or even disable if a gso skb is linearized in guest.

To solves those issues, this patch introduces an upper limit (PAGE_SIZE) of the
head, which guarantees an order 0 allocation each time.

Cc: Stefan Hajnoczi <stefanha@redhat.com>
Cc: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Jason Wang <jasowang@redhat.com>
---
The patch was needed for stable.
---
 drivers/net/macvtap.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/drivers/net/macvtap.c b/drivers/net/macvtap.c
index 9dccb1e..7ee6f9d 100644
--- a/drivers/net/macvtap.c
+++ b/drivers/net/macvtap.c
@@ -523,6 +523,11 @@ static inline struct sk_buff *macvtap_alloc_skb(struct sock *sk, size_t prepad,
 						int noblock, int *err)
 {
 	struct sk_buff *skb;
+	int good_linear = SKB_MAX_HEAD(prepad);
+
+	/* Don't use huge linear part */
+	if (linear > good_linear)
+		linear = good_linear;
 
 	/* Under a page?  Don't bother with paged skb. */
 	if (prepad + len < PAGE_SIZE || !linear)
-- 
1.8.3.2

Re: [PATCH net 2/2] macvtap: limit head length of skb allocated

[Michael S. Tsirkin]

On Tue, Nov 12, 2013 at 06:02:57PM +0800, Jason Wang wrote:
> We currently use hdr_len as a hint of head length which is advertised by
> guest. But when guest advertise a very big value, it can lead to an 64K+
> allocating of kmalloc() which has a very high possibility of failure when host
> memory is fragmented or under heavy stress. The huge hdr_len also reduce the
> effect of zerocopy or even disable if a gso skb is linearized in guest.
> 
> To solves those issues, this patch introduces an upper limit (PAGE_SIZE) of the
> head, which guarantees an order 0 allocation each time.
> 
> Cc: Stefan Hajnoczi <stefanha@redhat.com>
> Cc: Michael S. Tsirkin <mst@redhat.com>
> Signed-off-by: Jason Wang <jasowang@redhat.com>

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

> ---
> The patch was needed for stable.
> ---
>  drivers/net/macvtap.c | 5 +++++
>  1 file changed, 5 insertions(+)
> 
> diff --git a/drivers/net/macvtap.c b/drivers/net/macvtap.c
> index 9dccb1e..7ee6f9d 100644
> --- a/drivers/net/macvtap.c
> +++ b/drivers/net/macvtap.c
> @@ -523,6 +523,11 @@ static inline struct sk_buff *macvtap_alloc_skb(struct sock *sk, size_t prepad,
>  						int noblock, int *err)
>  {
>  	struct sk_buff *skb;
> +	int good_linear = SKB_MAX_HEAD(prepad);
> +
> +	/* Don't use huge linear part */
> +	if (linear > good_linear)
> +		linear = good_linear;
>  
>  	/* Under a page?  Don't bother with paged skb. */
>  	if (prepad + len < PAGE_SIZE || !linear)
> -- 
> 1.8.3.2
> 
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Re: [PATCH net 2/2] macvtap: limit head length of skb allocated

[Greg Rose]

On Tue, 12 Nov 2013 18:02:57 +0800
Jason Wang <jasowang@redhat.com> wrote:

> We currently use hdr_len as a hint of head length which is advertised
> by guest. But when guest advertise a very big value, it can lead to
> an 64K+ allocating of kmalloc() which has a very high possibility of
> failure when host memory is fragmented or under heavy stress. The
> huge hdr_len also reduce the effect of zerocopy or even disable if a
> gso skb is linearized in guest.
> 
> To solves those issues, this patch introduces an upper limit
> (PAGE_SIZE) of the head, which guarantees an order 0 allocation each
> time.
> 
> Cc: Stefan Hajnoczi <stefanha@redhat.com>
> Cc: Michael S. Tsirkin <mst@redhat.com>
> Signed-off-by: Jason Wang <jasowang@redhat.com>
> ---
> The patch was needed for stable.
> ---
>  drivers/net/macvtap.c | 5 +++++
>  1 file changed, 5 insertions(+)
> 
> diff --git a/drivers/net/macvtap.c b/drivers/net/macvtap.c
> index 9dccb1e..7ee6f9d 100644
> --- a/drivers/net/macvtap.c
> +++ b/drivers/net/macvtap.c
> @@ -523,6 +523,11 @@ static inline struct sk_buff
> *macvtap_alloc_skb(struct sock *sk, size_t prepad, int noblock, int
> *err) {
>  	struct sk_buff *skb;
> +	int good_linear = SKB_MAX_HEAD(prepad);
> +
> +	/* Don't use huge linear part */
> +	if (linear > good_linear)
> +		linear = good_linear;
>  
>  	/* Under a page?  Don't bother with paged skb. */
>  	if (prepad + len < PAGE_SIZE || !linear)

I see no problem with this or the tuntap patch except that in both
cases kernel coding style would prefer that you align the local
variable declarations in a reverse pyramid, longest at the beginning,
shortest at the end.

- Greg

Re: [PATCH net 2/2] macvtap: limit head length of skb allocated

[Jason Wang]

On 11/13/2013 01:45 AM, Greg Rose wrote:
> On Tue, 12 Nov 2013 18:02:57 +0800
> Jason Wang <jasowang@redhat.com> wrote:
>
>> We currently use hdr_len as a hint of head length which is advertised
>> by guest. But when guest advertise a very big value, it can lead to
>> an 64K+ allocating of kmalloc() which has a very high possibility of
>> failure when host memory is fragmented or under heavy stress. The
>> huge hdr_len also reduce the effect of zerocopy or even disable if a
>> gso skb is linearized in guest.
>>
>> To solves those issues, this patch introduces an upper limit
>> (PAGE_SIZE) of the head, which guarantees an order 0 allocation each
>> time.
>>
>> Cc: Stefan Hajnoczi <stefanha@redhat.com>
>> Cc: Michael S. Tsirkin <mst@redhat.com>
>> Signed-off-by: Jason Wang <jasowang@redhat.com>
>> ---
>> The patch was needed for stable.
>> ---
>>  drivers/net/macvtap.c | 5 +++++
>>  1 file changed, 5 insertions(+)
>>
>> diff --git a/drivers/net/macvtap.c b/drivers/net/macvtap.c
>> index 9dccb1e..7ee6f9d 100644
>> --- a/drivers/net/macvtap.c
>> +++ b/drivers/net/macvtap.c
>> @@ -523,6 +523,11 @@ static inline struct sk_buff
>> *macvtap_alloc_skb(struct sock *sk, size_t prepad, int noblock, int
>> *err) {
>>  	struct sk_buff *skb;
>> +	int good_linear = SKB_MAX_HEAD(prepad);
>> +
>> +	/* Don't use huge linear part */
>> +	if (linear > good_linear)
>> +		linear = good_linear;
>>  
>>  	/* Under a page?  Don't bother with paged skb. */
>>  	if (prepad + len < PAGE_SIZE || !linear)
> I see no problem with this or the tuntap patch except that in both
> cases kernel coding style would prefer that you align the local
> variable declarations in a reverse pyramid, longest at the beginning,
> shortest at the end.
>
> - Greg

Sure, will do it in V2.
Thanks
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Re: [PATCH net 1/2] tuntap: limit head length of skb allocated

[Michael S. Tsirkin]

On Tue, Nov 12, 2013 at 06:02:56PM +0800, Jason Wang wrote:
> We currently use hdr_len as a hint of head length which is advertised by
> guest. But when guest advertise a very big value, it can lead to an 64K+
> allocating of kmalloc() which has a very high possibility of failure when host
> memory is fragmented or under heavy stress. The huge hdr_len also reduce the
> effect of zerocopy or even disable if a gso skb is linearized in guest.
> 
> To solves those issues, this patch introduces an upper limit (PAGE_SIZE) of the
> head, which guarantees an order 0 allocation each time.
> 
> Cc: Stefan Hajnoczi <stefanha@redhat.com>
> Cc: Michael S. Tsirkin <mst@redhat.com>
> Signed-off-by: Jason Wang <jasowang@redhat.com>

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

> ---
> The patch was needed for stable.
> ---
>  drivers/net/tun.c | 5 +++++
>  1 file changed, 5 insertions(+)
> 
> diff --git a/drivers/net/tun.c b/drivers/net/tun.c
> index 7cb105c..5537b65 100644
> --- a/drivers/net/tun.c
> +++ b/drivers/net/tun.c
> @@ -954,6 +954,11 @@ static struct sk_buff *tun_alloc_skb(struct tun_file *tfile,
>  	struct sock *sk = tfile->socket.sk;
>  	struct sk_buff *skb;
>  	int err;
> +	int good_linear = SKB_MAX_HEAD(prepad);
> +
> +	/* Don't use huge linear part */
> +	if (linear > good_linear)
> +		linear = good_linear;
>  
>  	/* Under a page?  Don't bother with paged skb. */
>  	if (prepad + len < PAGE_SIZE || !linear)
> -- 
> 1.8.3.2
> 
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Re: [PATCH net 1/2] tuntap: limit head length of skb allocated

[Jason Wang]

----- 原始邮件 -----
> We currently use hdr_len as a hint of head length which is advertised by
> guest. But when guest advertise a very big value, it can lead to an 64K+
> allocating of kmalloc() which has a very high possibility of failure when
> host
> memory is fragmented or under heavy stress. The huge hdr_len also reduce the
> effect of zerocopy or even disable if a gso skb is linearized in guest.
> 
> To solves those issues, this patch introduces an upper limit (PAGE_SIZE) of
> the
> head, which guarantees an order 0 allocation each time.
> 
> Cc: Stefan Hajnoczi <stefanha@redhat.com>
> Cc: Michael S. Tsirkin <mst@redhat.com>
> Signed-off-by: Jason Wang <jasowang@redhat.com>
> ---
> The patch was needed for stable.
> ---
>  drivers/net/tun.c | 5 +++++
>  1 file changed, 5 insertions(+)
> 
> diff --git a/drivers/net/tun.c b/drivers/net/tun.c
> index 7cb105c..5537b65 100644
> --- a/drivers/net/tun.c
> +++ b/drivers/net/tun.c
> @@ -954,6 +954,11 @@ static struct sk_buff *tun_alloc_skb(struct tun_file
> *tfile,
>  	struct sock *sk = tfile->socket.sk;
>  	struct sk_buff *skb;
>  	int err;
> +	int good_linear = SKB_MAX_HEAD(prepad);
> +
> +	/* Don't use huge linear part */
> +	if (linear > good_linear)
> +		linear = good_linear;
>  
>  	/* Under a page?  Don't bother with paged skb. */
>  	if (prepad + len < PAGE_SIZE || !linear)
> --
> 1.8.3.2
> 

Looks like reduce the linear here will cause callers' iov_pages() under estimation.
Will send V2.
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