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Furthermore for 64-bit PV domains the area > is inaccessible (and hence cannot be updated by Xen) when in guest-user > mode. > > Introduce a new vCPU operation allowing to register the secondary time > area by guest-physical address. > > An at least theoretical downside to using physically registered areas is > that PV then won't see dirty (and perhaps also accessed) bits set in its > respective page table entries. > > Signed-off-by: Jan Beulich Reviewed-by: Roger Pau Monné > --- > v3: Re-base. > v2: Forge version in force_update_secondary_system_time(). > > --- a/xen/arch/x86/domain.c > +++ b/xen/arch/x86/domain.c > @@ -1504,6 +1504,15 @@ int arch_vcpu_reset(struct vcpu *v) > return 0; > } > > +static void cf_check > +time_area_populate(void *map, struct vcpu *v) > +{ > + if ( is_pv_vcpu(v) ) > + v->arch.pv.pending_system_time.version = 0; > + > + force_update_secondary_system_time(v, map); > +} > + > long do_vcpu_op(int cmd, unsigned int vcpuid, XEN_GUEST_HANDLE_PARAM(void) arg) > { > long rc = 0; > @@ -1541,6 +1550,25 @@ long do_vcpu_op(int cmd, unsigned int vc > > break; > } > + > + case VCPUOP_register_vcpu_time_phys_area: > + { > + struct vcpu_register_time_memory_area area; > + > + rc = -EFAULT; > + if ( copy_from_guest(&area.addr.p, arg, 1) ) > + break; > + > + rc = map_guest_area(v, area.addr.p, > + sizeof(vcpu_time_info_t), > + &v->arch.time_guest_area, > + time_area_populate); > + if ( rc == -ERESTART ) > + rc = hypercall_create_continuation(__HYPERVISOR_vcpu_op, "iih", > + cmd, vcpuid, arg); > + > + break; > + } > > case VCPUOP_get_physid: > { > --- a/xen/arch/x86/include/asm/domain.h > +++ b/xen/arch/x86/include/asm/domain.h > @@ -692,6 +692,8 @@ void domain_cpu_policy_changed(struct do > > bool update_secondary_system_time(struct vcpu *, > struct vcpu_time_info *); > +void force_update_secondary_system_time(struct vcpu *, > + struct vcpu_time_info *); > > void vcpu_show_registers(const struct vcpu *); > > --- a/xen/arch/x86/time.c > +++ b/xen/arch/x86/time.c > @@ -1633,6 +1633,16 @@ void force_update_vcpu_system_time(struc > __update_vcpu_system_time(v, 1); > } > > +void force_update_secondary_system_time(struct vcpu *v, > + struct vcpu_time_info *map) > +{ > + struct vcpu_time_info u; > + > + collect_time_info(v, &u); > + u.version = -1; /* Compensate for version_update_end(). */ Hm, we do not seem to compensate in VCPUOP_register_vcpu_time_memory_area, what's more, in that case the initial version is picked from the contents of the guest address. Hopefully the guest will have zeroed the memory. FWIW, I would be fine with leaving this at 0, so the first version guest sees is 1. Thanks, Roger.