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Re: [PATCH v3 8/8] xen/dom0less: store xenstore event channel in page
- To: Jan Beulich <jbeulich@xxxxxxxx>
- From: Jason Andryuk <jason.andryuk@xxxxxxx>
- Date: Wed, 27 Aug 2025 09:19:42 -0400
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- Cc: Stefano Stabellini <sstabellini@xxxxxxxxxx>, Julien Grall <julien@xxxxxxx>, Bertrand Marquis <bertrand.marquis@xxxxxxx>, Michal Orzel <michal.orzel@xxxxxxx>, <xen-devel@xxxxxxxxxxxxxxxxxxxx>
- Delivery-date: Wed, 27 Aug 2025 13:19:36 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
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.
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
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