Re: [Xen-devel] [PATCH v3 2/2] Xen: Use the ioreq-server API when available

[Peter Maydell <peter.maydell@xxxxxxxxxx>]

On 15 October 2014 11:16, Paul Durrant <paul.durrant@xxxxxxxxxx> wrote:
> The ioreq-server API added to Xen 4.5 offers better security than
> the existing Xen/QEMU interface because the shared pages that are
> used to pass emulation request/results back and forth are removed
> from the guest's memory space before any requests are serviced.
> This prevents the guest from mapping these pages (they are in a
> well known location) and attempting to attack QEMU by synthesizing
> its own request structures. Hence, this patch modifies configure
> to detect whether the API is available, and adds the necessary
> code to use the API if it is.

This commit message doesn't mention it, but presumably this is
all x86-specific given it's in a file which is only used for
x86 Xen?

> +static void xen_hvm_pre_save(void *opaque)
> +{
> +    XenIOState *state = opaque;
> +
> +    /* Stop servicing emulation requests */
> +    xen_set_ioreq_server_state(xen_xc, xen_domid, state->ioservid, 0);
> +    xen_destroy_ioreq_server(xen_xc, xen_domid, state->ioservid);
> +}
> +
> +static const VMStateDescription vmstate_xen_hvm = {
> +    .name = "xen-hvm",
> +    .version_id = 4,
> +    .minimum_version_id = 4,

This is new in upstream so why's it starting at version 4?

> +    .pre_save = xen_hvm_pre_save,
> +    .fields = (VMStateField[]) {
> +        VMSTATE_END_OF_LIST()
> +    },

A vmstate which doesn't actually save any state? This seems
rather suspicious...

> @@ -1060,12 +1185,19 @@ int xen_hvm_init(ram_addr_t *below_4g_mem_size, 
> ram_addr_t *above_4g_mem_size,
>      xen_ram_init(below_4g_mem_size, above_4g_mem_size, ram_size, ram_memory);
>
>      qemu_add_vm_change_state_handler(xen_hvm_change_state_handler, state);
> +    vmstate_register(NULL, 0, &vmstate_xen_hvm, state);

Is the new use of vmstate_register() really necessary?
Usually the state you're saving corresponds to some QOM
device whose vmsd field you can use instead.

thanks
-- PMM

_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxx
http://lists.xen.org/xen-devel