On 27.08.2025 15:19, Jason Andryuk wrote:
> On 2025-08-27 03:58, Jan Beulich wrote:
>> 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).
>
> Yes, that could be done, but it's not my preferred approach. Using a
> function pointer to pass a compile time constant seems to me like a
> misuse of a function pointer.
>
> I'd rather each arch using dom0less define:
> unsigned long copy_to_guest_phys(struct domain *d,
> paddr_t gpa,
> void *buf,
> unsigned int len);
>
> Which does the correct thing for the arch.
That would be even better, just that I don't know whether Arm folks would
like it.
Jan
> Alejandro was able to re-work things to re-use the dom0less parsing code
> (dom0less-bindings.c), but he has so far kept the x86 domain
> construction separate such that it does not use dom0less-build.c. So I
> don't know how that will shake out.
>
> But, yeah, I can just pass in a function pointer if that is what is
> agreed upon.
>
> Regards,
> Jason
