[Xen-devel] [XEN PATCH] x86/domctl: Have XEN_DOMCTL_getpageframeinfo3 preemptible

[Anthony PERARD <anthony.perard@xxxxxxxxxx>]

This hypercall can take a long time to finish because it attempts to
grab the `hostp2m' lock up to 1024 times. The accumulated wait for the
lock can take several seconds.

This can easily happen with a guest with 32 vcpus and plenty of RAM,
during localhost migration.

Signed-off-by: Anthony PERARD <anthony.perard@xxxxxxxxxx>
---

Notes:
    I don't know if it's a correct way to make the hypercall preemptible,
    the patch kind of modify the response, but libxc doesn't seems to care.
    
    Is it fine to modify the domctl_t that the domain (dom0) provides?
    If not, where could we store the progress made?

 xen/arch/x86/domctl.c | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/xen/arch/x86/domctl.c b/xen/arch/x86/domctl.c
index 43e368d63bb9..5c0a7462e63b 100644
--- a/xen/arch/x86/domctl.c
+++ b/xen/arch/x86/domctl.c
@@ -425,6 +425,18 @@ long arch_do_domctl(
                 ret = -EFAULT;
                 break;
             }
+
+            if ( hypercall_preempt_check() ) {
+                domctl->u.getpageframeinfo3.num = num - i - 1;
+                domctl->u.getpageframeinfo3.array.p =
+                    guest_handle + ((i + 1) * width);
+                if ( __copy_to_guest(u_domctl, domctl, 1) ) {
+                    ret = -EFAULT;
+                    break;
+                }
+                return hypercall_create_continuation(__HYPERVISOR_domctl,
+                                                     "h", u_domctl);
+            }
         }
 
         break;
-- 
Anthony PERARD


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