Re: [PATCH v3 8/8] xen/dom0less: store xenstore event channel in page

[Jan Beulich <jbeulich@suse.com>]

On 26.08.2025 23:08, Jason Andryuk wrote:
> --- a/xen/common/device-tree/dom0less-build.c
> +++ b/xen/common/device-tree/dom0less-build.c
> @@ -26,6 +26,7 @@
>  #include <public/event_channel.h>
>  #include <public/io/xs_wire.h>
>  
> +#include <asm/guest_access.h>
>  #include <asm/setup.h>
>  
>  #include <xen/static-memory.h>
> @@ -120,8 +121,14 @@ static void __init initialize_domU_xenstore(void)
>  
>          if ( gfn != XENSTORE_PFN_LATE_ALLOC && IS_ENABLED(CONFIG_GRANT_TABLE) )
>          {
> +            evtchn_port_t port = d->arch.hvm.params[HVM_PARAM_STORE_EVTCHN];
> +            paddr_t evtchn_gaddr = gfn_to_gaddr(_gfn(gfn)) +
> +                offsetof(struct xenstore_domain_interface, evtchn_port);
> +
>              ASSERT(gfn < UINT32_MAX);
>              gnttab_seed_entry(d, GNTTAB_RESERVED_XENSTORE, xs_domid, gfn);
> +            access_guest_memory_by_gpa(d, evtchn_gaddr, &port, sizeof(port),
> +                                       true /* is_write */);

Isn't the use of an arch-specific function going to pose yet another issue
for making this code usable on x86? Can't you use copy_to_guest_phys() here?
Which may in turn need to be passed in by the caller, see e.g. dtb_load()
and initrd_load() (i.e. cache flushing may also be necessary for Arm).

Jan