On Wed, May 03, 2023 at 05:57:40PM +0200, Jan Beulich wrote:
> The registration by virtual/linear address has downsides: At least on
> x86 the access is expensive for HVM/PVH domains. 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 runstate 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 <jbeul...@suse.com>
Reviewed-by: Roger Pau Monné <roger....@citrix.com>
One comment below.
> --- a/xen/include/public/vcpu.h
> +++ b/xen/include/public/vcpu.h
> @@ -221,6 +221,19 @@ struct vcpu_register_time_memory_area {
> typedef struct vcpu_register_time_memory_area
> vcpu_register_time_memory_area_t;
> DEFINE_XEN_GUEST_HANDLE(vcpu_register_time_memory_area_t);
>
> +/*
> + * Like the respective VCPUOP_register_*_memory_area, just using the "addr.p"
> + * field of the supplied struct as a guest physical address (i.e. in GFN
> space).
> + * The respective area may not cross a page boundary. Pass ~0 to unregister
> an
> + * area. Note that as long as an area is registered by physical address, the
> + * linear address based area will not be serviced (updated) by the
> hypervisor.
> + *
> + * Note that the area registered via VCPUOP_register_runstate_memory_area
> will
> + * be updated in the same manner as the one registered via virtual address
> PLUS
> + * VMASST_TYPE_runstate_update_flag engaged by the domain.
> + */
> +#define VCPUOP_register_runstate_phys_area 14
Just to make it more obvious, it might be nice to add a note in the
comment on VCPUOP_register_runstate_memory_area that `p` can also be
used with the `VCPUOP_register_runstate_phys_area` hypercall.
Thanks, Roger.
