re: virtio_net: support device stats

re: virtio_net: support device stats

[Colin King (gmail)]

Hi,

Static analysis on Linux-next has detected a potential issue with the 
following commit:

commit 941168f8b40e50518a3bc6ce770a7062a5d99230
Author: Xuan Zhuo <xuanzhuo@linux.alibaba.com>
Date:   Fri Apr 26 11:39:24 2024 +0800

     virtio_net: support device stats


The issue is in function virtnet_stats_ctx_init, in 
drivers/net/virtio_net.c as follows:

         if (vi->device_stats_cap & VIRTIO_NET_STATS_TYPE_CVQ) {
                 queue_type = VIRTNET_Q_TYPE_CQ;

                 ctx->bitmap[queue_type]   |= VIRTIO_NET_STATS_TYPE_CVQ;
                 ctx->desc_num[queue_type] += 
ARRAY_SIZE(virtnet_stats_cvq_desc);
                 ctx->size[queue_type]     += sizeof(struct 
virtio_net_stats_cvq);
         }


ctx->bitmap is declared as a u32 however it is being bit-wise or'd with 
VIRTIO_NET_STATS_TYPE_CVQ and this is defined as 1 << 32:

include/uapi/linux/virtio_net.h:#define VIRTIO_NET_STATS_TYPE_CVQ 
(1ULL << 32)

..and hence the bit-wise or operation won't set any bits in ctx->bitmap 
because 1ULL < 32 is too wide for a u32. I suspect ctx->bitmap should be 
declared as u64.

Colin

Re: virtio_net: support device stats

[Michael S. Tsirkin]

On Mon, Oct 14, 2024 at 10:39:26AM +0100, Colin King (gmail) wrote:
> Hi,
> 
> Static analysis on Linux-next has detected a potential issue with the
> following commit:
> 
> commit 941168f8b40e50518a3bc6ce770a7062a5d99230
> Author: Xuan Zhuo <xuanzhuo@linux.alibaba.com>
> Date:   Fri Apr 26 11:39:24 2024 +0800
> 
>     virtio_net: support device stats
> 
> 
> The issue is in function virtnet_stats_ctx_init, in drivers/net/virtio_net.c
> as follows:
> 
>         if (vi->device_stats_cap & VIRTIO_NET_STATS_TYPE_CVQ) {
>                 queue_type = VIRTNET_Q_TYPE_CQ;
> 
>                 ctx->bitmap[queue_type]   |= VIRTIO_NET_STATS_TYPE_CVQ;
>                 ctx->desc_num[queue_type] +=
> ARRAY_SIZE(virtnet_stats_cvq_desc);
>                 ctx->size[queue_type]     += sizeof(struct
> virtio_net_stats_cvq);
>         }
> 
> 
> ctx->bitmap is declared as a u32 however it is being bit-wise or'd with
> VIRTIO_NET_STATS_TYPE_CVQ and this is defined as 1 << 32:
> 
> include/uapi/linux/virtio_net.h:#define VIRTIO_NET_STATS_TYPE_CVQ (1ULL <<
> 32)
> 
> ..and hence the bit-wise or operation won't set any bits in ctx->bitmap
> because 1ULL < 32 is too wide for a u32.

Indeed. Xuan Zhuo how did you test this patch?

> I suspect ctx->bitmap should be
> declared as u64.
> 
> Colin
> 
> 

In fact, it is read into a u64:

       u64 offset, bitmap;
....
        bitmap = ctx->bitmap[queue_type];

we'll have to reorder fields to avoid wasting memory.
Like this I guess:

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

Colin, can you confirm pls?

diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index c6af18948092..ef221429f784 100644
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c
@@ -4111,12 +4111,12 @@ struct virtnet_stats_ctx {
 	/* Used to calculate the offset inside the output buffer. */
 	u32 desc_num[3];
 
-	/* The actual supported stat types. */
-	u32 bitmap[3];
-
 	/* Used to calculate the reply buffer size. */
 	u32 size[3];
 
+	/* The actual supported stat types. */
+	u64 bitmap[3];
+
 	/* Record the output buffer. */
 	u64 *data;
 };
-- 
MST

Re: virtio_net: support device stats

[Colin King (gmail)]

On 14/10/2024 10:47, Michael S. Tsirkin wrote:
> On Mon, Oct 14, 2024 at 10:39:26AM +0100, Colin King (gmail) wrote:
>> Hi,
>>
>> Static analysis on Linux-next has detected a potential issue with the
>> following commit:
>>
>> commit 941168f8b40e50518a3bc6ce770a7062a5d99230
>> Author: Xuan Zhuo <xuanzhuo@linux.alibaba.com>
>> Date:   Fri Apr 26 11:39:24 2024 +0800
>>
>>      virtio_net: support device stats
>>
>>
>> The issue is in function virtnet_stats_ctx_init, in drivers/net/virtio_net.c
>> as follows:
>>
>>          if (vi->device_stats_cap & VIRTIO_NET_STATS_TYPE_CVQ) {
>>                  queue_type = VIRTNET_Q_TYPE_CQ;
>>
>>                  ctx->bitmap[queue_type]   |= VIRTIO_NET_STATS_TYPE_CVQ;
>>                  ctx->desc_num[queue_type] +=
>> ARRAY_SIZE(virtnet_stats_cvq_desc);
>>                  ctx->size[queue_type]     += sizeof(struct
>> virtio_net_stats_cvq);
>>          }
>>
>>
>> ctx->bitmap is declared as a u32 however it is being bit-wise or'd with
>> VIRTIO_NET_STATS_TYPE_CVQ and this is defined as 1 << 32:
>>
>> include/uapi/linux/virtio_net.h:#define VIRTIO_NET_STATS_TYPE_CVQ (1ULL <<
>> 32)
>>
>> ..and hence the bit-wise or operation won't set any bits in ctx->bitmap
>> because 1ULL < 32 is too wide for a u32.
> 
> Indeed. Xuan Zhuo how did you test this patch?
> 
>> I suspect ctx->bitmap should be
>> declared as u64.
>>
>> Colin
>>
>>
> 
> In fact, it is read into a u64:
> 
>         u64 offset, bitmap;
> ....
>          bitmap = ctx->bitmap[queue_type];
> 
> we'll have to reorder fields to avoid wasting memory.
> Like this I guess:
> 
> Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
> 
> Colin, can you confirm pls?

Fix looks sane to be, with u64 bitmap[3] struct size field re-ordering 
does not seem to make any difference on x86-64 (64 bytes) and i586 (56 
bytes) when I compiled with gcc-12, gcc-14 and clang-20.

I can't functionally test this though (not sure how).

Reviewed-by: Colin Ian King <colin.king@gmail.com>

> 
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index c6af18948092..ef221429f784 100644
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
> @@ -4111,12 +4111,12 @@ struct virtnet_stats_ctx {
>   	/* Used to calculate the offset inside the output buffer. */
>   	u32 desc_num[3];
>   
> -	/* The actual supported stat types. */
> -	u32 bitmap[3];
> -
>   	/* Used to calculate the reply buffer size. */
>   	u32 size[3];
>   
> +	/* The actual supported stat types. */
> +	u64 bitmap[3];
> +
>   	/* Record the output buffer. */
>   	u64 *data;
>   };

Re: virtio_net: support device stats

[Xuan Zhuo]

On Mon, 14 Oct 2024 05:47:41 -0400, "Michael S. Tsirkin" <mst@redhat.com> wrote:
> On Mon, Oct 14, 2024 at 10:39:26AM +0100, Colin King (gmail) wrote:
> > Hi,
> >
> > Static analysis on Linux-next has detected a potential issue with the
> > following commit:
> >
> > commit 941168f8b40e50518a3bc6ce770a7062a5d99230
> > Author: Xuan Zhuo <xuanzhuo@linux.alibaba.com>
> > Date:   Fri Apr 26 11:39:24 2024 +0800
> >
> >     virtio_net: support device stats
> >
> >
> > The issue is in function virtnet_stats_ctx_init, in drivers/net/virtio_net.c
> > as follows:
> >
> >         if (vi->device_stats_cap & VIRTIO_NET_STATS_TYPE_CVQ) {
> >                 queue_type = VIRTNET_Q_TYPE_CQ;
> >
> >                 ctx->bitmap[queue_type]   |= VIRTIO_NET_STATS_TYPE_CVQ;
> >                 ctx->desc_num[queue_type] +=
> > ARRAY_SIZE(virtnet_stats_cvq_desc);
> >                 ctx->size[queue_type]     += sizeof(struct
> > virtio_net_stats_cvq);
> >         }
> >
> >
> > ctx->bitmap is declared as a u32 however it is being bit-wise or'd with
> > VIRTIO_NET_STATS_TYPE_CVQ and this is defined as 1 << 32:
> >
> > include/uapi/linux/virtio_net.h:#define VIRTIO_NET_STATS_TYPE_CVQ (1ULL <<
> > 32)
> >
> > ..and hence the bit-wise or operation won't set any bits in ctx->bitmap
> > because 1ULL < 32 is too wide for a u32.
>
> Indeed. Xuan Zhuo how did you test this patch?

In our machines, cvq type is not supported. ^_^

Why gcc has not warning for this, or I missed it.

>
> > I suspect ctx->bitmap should be
> > declared as u64.
> >
> > Colin
> >
> >
>
> In fact, it is read into a u64:
>
>        u64 offset, bitmap;
> ....
>         bitmap = ctx->bitmap[queue_type];
>
> we'll have to reorder fields to avoid wasting memory.
> Like this I guess:
>
> Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

Reviewed-by: Xuan Zhuo <xuanzhuo@linux.alibaba.com>

Thanks

>
> Colin, can you confirm pls?
>
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index c6af18948092..ef221429f784 100644
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
> @@ -4111,12 +4111,12 @@ struct virtnet_stats_ctx {
>  	/* Used to calculate the offset inside the output buffer. */
>  	u32 desc_num[3];
>
> -	/* The actual supported stat types. */
> -	u32 bitmap[3];
> -
>  	/* Used to calculate the reply buffer size. */
>  	u32 size[3];
>
> +	/* The actual supported stat types. */
> +	u64 bitmap[3];
> +
>  	/* Record the output buffer. */
>  	u64 *data;
>  };
> --
> MST
>

Re: virtio_net: support device stats

[Jason Wang]

On Mon, Oct 14, 2024 at 6:15 PM Colin King (gmail)
<colin.i.king@gmail.com> wrote:
>
> On 14/10/2024 10:47, Michael S. Tsirkin wrote:
> > On Mon, Oct 14, 2024 at 10:39:26AM +0100, Colin King (gmail) wrote:
> >> Hi,
> >>
> >> Static analysis on Linux-next has detected a potential issue with the
> >> following commit:
> >>
> >> commit 941168f8b40e50518a3bc6ce770a7062a5d99230
> >> Author: Xuan Zhuo <xuanzhuo@linux.alibaba.com>
> >> Date:   Fri Apr 26 11:39:24 2024 +0800
> >>
> >>      virtio_net: support device stats
> >>
> >>
> >> The issue is in function virtnet_stats_ctx_init, in drivers/net/virtio_net.c
> >> as follows:
> >>
> >>          if (vi->device_stats_cap & VIRTIO_NET_STATS_TYPE_CVQ) {
> >>                  queue_type = VIRTNET_Q_TYPE_CQ;
> >>
> >>                  ctx->bitmap[queue_type]   |= VIRTIO_NET_STATS_TYPE_CVQ;
> >>                  ctx->desc_num[queue_type] +=
> >> ARRAY_SIZE(virtnet_stats_cvq_desc);
> >>                  ctx->size[queue_type]     += sizeof(struct
> >> virtio_net_stats_cvq);
> >>          }
> >>
> >>
> >> ctx->bitmap is declared as a u32 however it is being bit-wise or'd with
> >> VIRTIO_NET_STATS_TYPE_CVQ and this is defined as 1 << 32:
> >>
> >> include/uapi/linux/virtio_net.h:#define VIRTIO_NET_STATS_TYPE_CVQ (1ULL <<
> >> 32)
> >>
> >> ..and hence the bit-wise or operation won't set any bits in ctx->bitmap
> >> because 1ULL < 32 is too wide for a u32.
> >
> > Indeed. Xuan Zhuo how did you test this patch?
> >
> >> I suspect ctx->bitmap should be
> >> declared as u64.
> >>
> >> Colin
> >>
> >>
> >
> > In fact, it is read into a u64:
> >
> >         u64 offset, bitmap;
> > ....
> >          bitmap = ctx->bitmap[queue_type];
> >
> > we'll have to reorder fields to avoid wasting memory.
> > Like this I guess:
> >
> > Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
> >
> > Colin, can you confirm pls?
>
> Fix looks sane to be, with u64 bitmap[3] struct size field re-ordering
> does not seem to make any difference on x86-64 (64 bytes) and i586 (56
> bytes) when I compiled with gcc-12, gcc-14 and clang-20.
>
> I can't functionally test this though (not sure how).
>
> Reviewed-by: Colin Ian King <colin.king@gmail.com>

Maybe it's time to ask for a prototype for each virtio-net feature
before it can be merged into the spec.

Thanks