On Thu, 10 Dec 2020 11:55:17 -0300
Daniel Henrique Barboza <danielhb...@gmail.com> wrote:
> spapr_kvm_type() is considering 'vm_type=NULL' as a valid input, where
> the function returns 0. This is relying on the current QEMU machine
> options handling logic, where the absence of the 'kvm-type' option
> will be reflected as 'vm_type=NULL' in this function.
>
> This is not robust, and will break if QEMU options code decides to propagate
> something else in the case mentioned above (e.g. an empty string instead
> of NULL).
>
> Let's avoid this entirely by setting a non-NULL default value in case of
> no user input for 'kvm-type'. spapr_kvm_type() was changed to handle 3 fixed
> values of kvm-type: "auto", "hv", and "pr", with "auto" being the default
> if no kvm-type was set by the user. This allows us to always be predictable
> regardless of any enhancements/changes made in QEMU options mechanics.
>
> While we're at it, let's also document in 'kvm-type' description the
> already existing default mode, now named 'auto'. The information provided
> about it is based on how the pseries kernel handles the KVM_CREATE_VM
> ioctl(), where the default value '0' makes the kernel choose an available
> KVM module to use, giving precedence to kvm_hv. This logic is described in
> the kernel source file arch/powerpc/kvm/powerpc.c, function
> kvm_arch_init_vm().
>
> Signed-off-by: Daniel Henrique Barboza <danielhb...@gmail.com>
> ---
Reviewed-by: Greg Kurz <gr...@kaod.org>
> hw/ppc/spapr.c | 21 +++++++++++++++++----
> 1 file changed, 17 insertions(+), 4 deletions(-)
>
> diff --git a/hw/ppc/spapr.c b/hw/ppc/spapr.c
> index b7e0894019..877bd264ce 100644
> --- a/hw/ppc/spapr.c
> +++ b/hw/ppc/spapr.c
> @@ -3021,17 +3021,25 @@ static void spapr_machine_init(MachineState *machine)
> qemu_cond_init(&spapr->fwnmi_machine_check_interlock_cond);
> }
>
> +#define DEFAULT_KVM_TYPE "auto"
> static int spapr_kvm_type(MachineState *machine, const char *vm_type)
> {
> - if (!vm_type) {
> + /*
> + * The use of g_ascii_strcasecmp() for 'hv' and 'pr' is to
> + * accomodate the 'HV' and 'PV' formats that exists in the
> + * wild. The 'auto' mode is being introduced already as
> + * lower-case, thus we don't need to bother checking for
> + * "AUTO".
> + */
> + if (!vm_type || !strcmp(vm_type, DEFAULT_KVM_TYPE)) {
> return 0;
> }
>
> - if (!strcmp(vm_type, "HV")) {
> + if (!g_ascii_strcasecmp(vm_type, "hv")) {
> return 1;
> }
>
> - if (!strcmp(vm_type, "PR")) {
> + if (!g_ascii_strcasecmp(vm_type, "pr")) {
> return 2;
> }
>
> @@ -3270,10 +3278,15 @@ static void spapr_instance_init(Object *obj)
>
> spapr->htab_fd = -1;
> spapr->use_hotplug_event_source = true;
> + spapr->kvm_type = g_strdup(DEFAULT_KVM_TYPE);
> object_property_add_str(obj, "kvm-type",
> spapr_get_kvm_type, spapr_set_kvm_type);
> object_property_set_description(obj, "kvm-type",
> - "Specifies the KVM virtualization mode
> (HV, PR)");
> + "Specifies the KVM virtualization mode
> (auto,"
> + " hv, pr). Defaults to 'auto'. This mode
> will use"
> + " any available KVM module loaded in the
> host,"
> + " where kvm_hv takes precedence if both
> kvm_hv and"
> + " kvm_pr are loaded.");
> object_property_add_bool(obj, "modern-hotplug-events",
> spapr_get_modern_hotplug_events,
> spapr_set_modern_hotplug_events);
