Re: [Xen-devel] [PATCH 11/22] vixen: early initialization of Vixen including shared_info mapping

[Roger Pau Monné <roger.pau@xxxxxxxxxx>]

On Sat, Jan 06, 2018 at 02:54:26PM -0800, Anthony Liguori wrote:
> From: Anthony Liguori <aliguori@xxxxxxxxxx>
> 
> We split initialization of Vixen into two parts.  The first part
> just detects the presence of an HVM hypervisor so that we can
> figure out whether to modify the e820 table.
> 
> The later initialization is used to actually map the shared_info
> structure from the parent hypervisor into Xen.
> 
> Signed-off-by: Anthony Liguori <aliguori@xxxxxxxxxx>
> ---
>  xen/arch/x86/guest/vixen.c        | 45 
> +++++++++++++++++++++++++++++++++++++++
>  xen/arch/x86/setup.c              |  5 +++++
>  xen/include/asm-x86/guest/vixen.h |  4 ++++
>  3 files changed, 54 insertions(+)
> 
> diff --git a/xen/arch/x86/guest/vixen.c b/xen/arch/x86/guest/vixen.c
> index d82e68f..d8466ba 100644
> --- a/xen/arch/x86/guest/vixen.c
> +++ b/xen/arch/x86/guest/vixen.c
> @@ -20,8 +20,53 @@
>   */
>  
>  #include <asm/guest/vixen.h>
> +#include <public/version.h>
>  
>  static int in_vixen;
> +static uint8_t global_si_data[4 << 10] __attribute__((aligned(4096)));

The shared_info memory page gfn doesn't need to be populated, by doing
it like this you are wasting a domain's memory page.

> +static shared_info_t *global_si = (void *)global_si_data;
> +
> +void __init init_vixen(void)
> +{
> +    int major, minor, version;
> +
> +    if ( !xen_guest )
> +    {
> +        printk("Disabling Vixen because we are not running under Xen\n");
> +        in_vixen = -1;
> +        return;
> +    }
> +
> +    version = HYPERVISOR_xen_version(XENVER_version, NULL);
> +    major = version >> 16;
> +    minor = version & 0xffff;
> +
> +    printk("Vixen running under Xen %d.%d\n", major, minor);
> +
> +    in_vixen = 1;
> +}
> +
> +void __init early_vixen_init(void)
> +{
> +    struct xen_add_to_physmap xatp;
> +    long rc;
> +
> +    if ( !is_vixen() )
> +     return;
> +
> +    /* Setup our own shared info area */
> +    xatp.domid = DOMID_SELF;
> +    xatp.idx = 0;
> +    xatp.space = XENMAPSPACE_shared_info;
> +    xatp.gpfn = virt_to_mfn(global_si);
> +
> +    rc = HYPERVISOR_memory_op(XENMEM_add_to_physmap, &xatp);
> +    if ( rc < 0 )
> +        printk("Setting shared info page failed: %ld\n", rc);
> +
> +    memset(&global_si->native.evtchn_mask[0], 0x00,
> +           sizeof(global_si->native.evtchn_mask));

Hm, I'm not sure I like to approach of unmasking everything. IMHO I
would rather mask everything and unmask them when the guest actually
binds the event channel. That makes sure that an interrupt will get
injected when the event channel is unmasked (if there's an event
pending).

Thanks, Roger.

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