Re: [PATCH v3] examples/vdpa: support running in nested virtualization environment

[Maxime Coquelin <maxime.coquelin@redhat.com>]

Hi Hao

On 10/25/22 08:19, Hao Chen wrote:
> When we run dpdk vdpa in the nested virtual machine vm-L1 and ping
> test in vm-L2, the ping is NG. The reason for troubleshooting is

NG == not good? Please don't use abbreviations.

> that the virtio net in vm-L2 sends control information to the vring,
> and the qemu back-end device in vm-L1 cannot obtain correct data
> from the vring. This problem is related to the opening of the vIOMMU.
> 
> This patch add option '--iommu-support' to use guest vIOMMU to
> protect vhost, then the ping test in vm-L2 is OK.
> This option is required in a nested virtualization environment.

I'm wondering whether the flag shouldn't just be set by default, as the
feature negotiation will be done between the vDPA driver & the guest
driver anyways?


> Signed-off-by: Hao Chen <chenh@yusur.tech>
> ---
> v3:
> *Modify mail title.
> 
> v2:
> *fprintf all string including the eal one.
> *remove exit(1).
> 
>   examples/vdpa/main.c | 17 ++++++++++++-----
>   1 file changed, 12 insertions(+), 5 deletions(-)
> 
> diff --git a/examples/vdpa/main.c b/examples/vdpa/main.c
> index 4c7e81d7b6..71149461c6 100644
> --- a/examples/vdpa/main.c
> +++ b/examples/vdpa/main.c
> @@ -43,16 +43,18 @@ static char iface[MAX_PATH_LEN];
>   static int devcnt;
>   static int interactive;
>   static int client_mode;
> +static int iommu_support;
>   
>   /* display usage */
>   static void
>   vdpa_usage(const char *prgname)
>   {
> -	printf("Usage: %s [EAL options] -- "
> -				 "	--interactive|-i: run in interactive mode.\n"
> -				 "	--iface <path>: specify the path prefix of the socket files, e.g. /tmp/vhost-user-.\n"
> -				 "	--client: register a vhost-user socket as client mode.\n",
> -				 prgname);
> +	const char *usage_str = "	--interactive|-i: run in interactive mode.\n"
> +				"	--iface <path>: specify the path prefix of the socket files, e.g. /tmp/vhost-user-.\n"
> +				"	--client: register a vhost-user socket as client mode.\n"
> +				"	--iommu-support: use guest vIOMMU to protect vhost.\n";
> +
> +	fprintf(stderr, "Usage: %s [EAL options] --\n%s", prgname, usage_str);
>   }
>   
>   static int
> @@ -63,6 +65,7 @@ parse_args(int argc, char **argv)
>   		{"iface", required_argument, NULL, 0},
>   		{"interactive", no_argument, &interactive, 1},
>   		{"client", no_argument, &client_mode, 1},
> +		{"iommu-support", no_argument, &iommu_support, 1},
>   		{NULL, 0, 0, 0},
>   	};
>   	int opt, idx;
> @@ -220,6 +223,10 @@ start_vdpa(struct vdpa_port *vport)
>   			socket_path);
>   		return -1;
>   	}
> +
> +	if (iommu_support)
> +		vport->flags |= RTE_VHOST_USER_IOMMU_SUPPORT;
> +
>   	ret = rte_vhost_driver_register(socket_path, vport->flags);
>   	if (ret != 0)
>   		rte_exit(EXIT_FAILURE,