Re: [PATCH v4 8/9] tools: add example application to initialize dom0less PV drivers

[Julien Grall <julien@xxxxxxx>]

Hi,

I have posted some comments in v3 after you sent this version. Please 
have a look.
On 01/04/2022 01:38, Stefano Stabellini wrote:
> +static int init_domain(struct xs_handle *xsh, libxl_dominfo *info)
> +{
> +    struct xc_interface_core *xch;
> +    libxl_uuid uuid;
> +    uint64_t xenstore_evtchn, xenstore_pfn;
> +    int rc;
> +
> +    printf("Init dom0less domain: %u\n", info->domid);
> +    xch = xc_interface_open(0, 0, 0);
> +
> +    rc = xc_hvm_param_get(xch, info->domid, HVM_PARAM_STORE_EVTCHN,
> +                          &xenstore_evtchn);
> +    if (rc != 0) {
> +        printf("Failed to get HVM_PARAM_STORE_EVTCHN\n");
> +        return 1;
> +    }
> +
> +    /* Alloc xenstore page */
> +    if (alloc_xs_page(xch, info, &xenstore_pfn) != 0) {
> +        printf("Error on alloc magic pages\n");
> +        return 1;
> +    }
> +
> +    rc = xc_dom_gnttab_seed(xch, info->domid, true,
> +                            (xen_pfn_t)-1, xenstore_pfn, 0, 0);
> +    if (rc)
> +        err(1, "xc_dom_gnttab_seed");
> +
> +    libxl_uuid_generate(&uuid);
> +    xc_domain_sethandle(xch, info->domid, libxl_uuid_bytearray(&uuid));
> +
> +    rc = gen_stub_json_config(info->domid, &uuid);
> +    if (rc)
> +        err(1, "gen_stub_json_config");
> +
> +    /* Now everything is ready: set HVM_PARAM_STORE_PFN */
> +    rc = xc_hvm_param_set(xch, info->domid, HVM_PARAM_STORE_PFN,
> +                          xenstore_pfn);
On patch #1, you told me you didn't want to allocate the page in Xen 
because it wouldn't be initialized by Xenstored. But this is what we are 
doing here.
This would be a problem if Linux is still booting and hasn't yet call 
xenbus_probe_initcall().
I understand we need to have the page setup before raising the event 
channel. I don't think we can allow Xenstored to set the HVM_PARAM (it 
may run in a domain with less privilege). So I think we may need to 
create a separate command to kick the client (not great).
Juergen, any thoughts?

Cheers,

--
Julien Grall