On Tue, Nov 08, 2016 at 04:56:10PM +1100, Alexey Kardashevskiy wrote:
> On 08/11/16 16:26, David Gibson wrote:
> > On Fri, Nov 04, 2016 at 06:43:52PM +1100, Alexey Kardashevskiy wrote:
> >> On 30/10/16 22:12, David Gibson wrote:
> >>> Server class POWER CPUs have a "compat" property, which is used to set the
> >>> backwards compatibility mode for the processor. However, this only makes
> >>> sense for machine types which don't give the guest access to hypervisor
> >>> privilege - otherwise the compatibility level is under the guest's
> >>> control.
> >>>
> >>> To reflect this, this removes the CPU 'compat' property and instead
> >>> creates a 'max-cpu-compat' property on the pseries machine. Strictly
> >>> speaking this breaks compatibility, but AFAIK the 'compat' option was
> >>> never (directly) used with -device or device_add.
> >>>
> >>> The option was used with -cpu. So, to maintain compatibility, this patch
> >>> adds a hack to the cpu option parsing to strip out any compat options
> >>> supplied with -cpu and set them on the machine property instead of the new
> >>> removed cpu property.
> >>>
> >>> Signed-off-by: David Gibson <da...@gibson.dropbear.id.au>
> >>> ---
> >>> hw/ppc/spapr.c | 6 +++-
> >>> hw/ppc/spapr_cpu_core.c | 47 +++++++++++++++++++++++++++--
> >>> hw/ppc/spapr_hcall.c | 2 +-
> >>> include/hw/ppc/spapr.h | 10 +++++--
> >>> target-ppc/compat.c | 65 ++++++++++++++++++++++++++++++++++++++++
> >>> target-ppc/cpu.h | 6 ++--
> >>> target-ppc/translate_init.c | 73
> >>> ---------------------------------------------
> >>> 7 files changed, 127 insertions(+), 82 deletions(-)
> >>>
> >>> diff --git a/hw/ppc/spapr.c b/hw/ppc/spapr.c
> >>> index 6c78889..b983faa 100644
> >>> --- a/hw/ppc/spapr.c
> >>> +++ b/hw/ppc/spapr.c
> >>> @@ -1849,7 +1849,7 @@ static void ppc_spapr_init(MachineState *machine)
> >>> machine->cpu_model = kvm_enabled() ? "host" :
> >>> smc->tcg_default_cpu;
> >>> }
> >>>
> >>> - ppc_cpu_parse_features(machine->cpu_model);
> >>> + spapr_cpu_parse_features(spapr);
> >>>
> >>> spapr_init_cpus(spapr);
> >>>
> >>> @@ -2191,6 +2191,10 @@ static void spapr_machine_initfn(Object *obj)
> >>> " place of standard EPOW events when
> >>> possible"
> >>> " (required for memory hot-unplug
> >>> support)",
> >>> NULL);
> >>> +
> >>> + object_property_add(obj, "max-cpu-compat", "str",
> >>> + ppc_compat_prop_get, ppc_compat_prop_set,
> >>> + NULL, &spapr->max_compat_pvr, &error_fatal);
> >>> }
> >>>
> >>> static void spapr_machine_finalizefn(Object *obj)
> >>> diff --git a/hw/ppc/spapr_cpu_core.c b/hw/ppc/spapr_cpu_core.c
> >>> index ee5cd14..0319516 100644
> >>> --- a/hw/ppc/spapr_cpu_core.c
> >>> +++ b/hw/ppc/spapr_cpu_core.c
> >>> @@ -18,6 +18,49 @@
> >>> #include "target-ppc/mmu-hash64.h"
> >>> #include "sysemu/numa.h"
> >>>
> >>> +void spapr_cpu_parse_features(sPAPRMachineState *spapr)
> >>> +{
> >>> + /*
> >>> + * Backwards compatibility hack:
> >>> +
> >>> + * CPUs had a "compat=" property which didn't make sense for
> >>> + * anything except pseries. It was replaced by "max-cpu-compat"
> >>> + * machine option. This supports old command lines like
> >>> + * -cpu POWER8,compat=power7
> >>> + * By stripping the compat option and applying it to the machine
> >>> + * before passing it on to the cpu level parser.
> >>> + */
> >>> + gchar **inpieces, **outpieces;
> >>> + int n, i, j;
> >>> + gchar *compat_str = NULL;
> >>> + gchar *filtered_model;
> >>> +
> >>> + inpieces = g_strsplit(MACHINE(spapr)->cpu_model, ",", 0);
> >>> + n = g_strv_length(inpieces);
> >>> + outpieces = g_new0(gchar *, g_strv_length(inpieces));
> >>> +
> >>> + /* inpieces[0] is the actual model string */
> >>> + for (i = 0, j = 0; i < n; i++) {
> >>> + if (g_str_has_prefix(inpieces[i], "compat=")) {
> >>> + compat_str = inpieces[i];
> >>> + } else {
> >>> + outpieces[j++] = g_strdup(inpieces[i]);
> >>> + }
> >>> + }
> >>> +
> >>> + if (compat_str) {
> >>> + char *val = compat_str + strlen("compat=");
> >>> + object_property_set_str(OBJECT(spapr), val, "max-cpu-compat",
> >>> + &error_fatal);
> >>
> >> This part is ok.
> >>
> >>> + }
> >>> +
> >>> + filtered_model = g_strjoinv(",", outpieces);
> >>> + ppc_cpu_parse_features(filtered_model);
> >>
> >>
> >> Rather than reducing the CPU parameters string from the command line, I'd
> >> keep "dc->props = powerpc_servercpu_properties" and make them noop + warn
> >> to use the machine option instead. One day QEMU may start calling the CPU
> >> features parser itself and somebody will have to hack this thing
> >> again.
> >
> > Hrm. A deprecation message like that only works if a human is reading
> > it. Usually qemu will be invoked by libvirt and the message will
> > probably disappear into some log file to scare someone unnecessarily.
> >
> > Meanwhile, what will the actual behaviour be? Pulling the CPU's
> > property value into the machine instead would be really ugly.
> > Ignoring it would break users with existing libvirt.
>
>
> I only suggested instead of removing "compat=" from the model string,
> - pass the model as is to ppc_cpu_parse_features() with no changes;
> - change powerpc_set_compat() to print a message and do nothing else, and
> add a comment there saying why it is so.
Ah, right, now I understand. Yes, that's a good idea. It will
greatly simplify the rather hideous string mangling, too.
> > The hack above is nasty, but I'm not really seeing a better option.
--
David Gibson | I'll have my music baroque, and my code
david AT gibson.dropbear.id.au | minimalist, thank you. NOT _the_ _other_
| _way_ _around_!
http://www.ozlabs.org/~dgibson
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