On 06/26/2014 12:11 PM, Prerna Saxena wrote:
> PowerISA allows processors to run VMs in binary compatibility ("compat")
> mode supporting an older version of ISA.
> Eg,in compatibility mode, a POWER8 host can run a "Power7" VM,conforming
> to PowerISA v2.06, while a POWER7 host can run a "POWER6" VM, conforming
> to PowerISA v2.05.
>
> QEMU has recently added support to explicitly denote a VM running in
> compatibility mode through commit 6d9412ea. Now, a "compat" mode VM can
> be run by invoking this qemu commandline on a POWER8 host:
> -cpu host,compat=power7
> as against the older specification of "-cpu power7".
>
> However, running in compatibility mode is not identical to running
> natively on an older processor. Hence the virtualization stack needs to
> explicitly provide for a compat-mode VM.
>
> This patch allows libvirt to extend the "fallback" semantics of cpu model to
> describe this new mode for PowerKVM guests.
> Additionally with the new scheme of things, qemu doesn't provide a way to query
> for the supported compat models and models returned when querying with '-cpu ?'
> are no longer valid. Hence removing the check cpuModelIsAllowed() for now.
>
> When a user wants to request a power7 vm to run in compatibility mode on
> a Power8 host, this can be described in XML as follows :
> <cpu mode='custom' match='exact'>
> <model fallback='compat'>power7</model>
> </cpu>
>
I think <model compat='power7'>host</model> with 'compat' being a separate
attribute would be nicer (and match what we pass to QEMU more closely),
but perhaps I'm not the most qualified person to judge that.
> An alternative approach could be to leave the libvirt XML intact, and merely
> change the backend qemu command generation when the VM-requested cpu
> does not match the host processor.
That seems too hack-ish for me.
>
> Looking forward to suggestions on how this can best be implemented..
>
> Signed-off-by: Li Zhang <zhlcindy@xxxxxxxxxxxxxxxxxx>
> Signed-off-by: Pradipta Kr. Banerjee <bpradip@xxxxxxxxxx>
> Signed-off-by: Prerna Saxena <prerna@xxxxxxxxxxxxxxxxxx>
>
> diff --git a/src/conf/cpu_conf.c b/src/conf/cpu_conf.c
> index ebdaa19..2f41bd7 100644
> --- a/src/conf/cpu_conf.c
> +++ b/src/conf/cpu_conf.c
> @@ -47,7 +47,8 @@ VIR_ENUM_IMPL(virCPUMatch, VIR_CPU_MATCH_LAST,
>
> VIR_ENUM_IMPL(virCPUFallback, VIR_CPU_FALLBACK_LAST,
> "allow",
> - "forbid")
> + "forbid",
> + "compat")
>
> VIR_ENUM_IMPL(virCPUFeaturePolicy, VIR_CPU_FEATURE_LAST,
> "force",
> diff --git a/src/conf/cpu_conf.h b/src/conf/cpu_conf.h
> index 8c932ce..50354f2 100644
> --- a/src/conf/cpu_conf.h
> +++ b/src/conf/cpu_conf.h
> @@ -65,6 +65,7 @@ VIR_ENUM_DECL(virCPUMatch)
> typedef enum {
> VIR_CPU_FALLBACK_ALLOW,
> VIR_CPU_FALLBACK_FORBID,
> + VIR_CPU_FALLBACK_COMPAT,
>
> VIR_CPU_FALLBACK_LAST
> } virCPUFallback;
> diff --git a/src/cpu/cpu_powerpc.c b/src/cpu/cpu_powerpc.c
> index b220448..218c013 100644
> --- a/src/cpu/cpu_powerpc.c
> +++ b/src/cpu/cpu_powerpc.c
> @@ -457,8 +457,8 @@ ppcCompare(virCPUDefPtr host,
> static int
> ppcDecode(virCPUDefPtr cpu,
> const virCPUData *data,
> - const char **models,
> - unsigned int nmodels,
> + const char **models ATTRIBUTE_UNUSED,
> + unsigned int nmodels ATTRIBUTE_UNUSED,
> const char *preferred ATTRIBUTE_UNUSED,
> unsigned int flags)
> {
> @@ -478,13 +478,6 @@ ppcDecode(virCPUDefPtr cpu,
> goto cleanup;
> }
>
> - if (!cpuModelIsAllowed(model->name, models, nmodels)) {
> - virReportError(VIR_ERR_CONFIG_UNSUPPORTED,
> - _("CPU model %s is not supported by hypervisor"),
> - model->name);
> - goto cleanup;
> - }
This validation shouldn't be skipped for all the models, just the compat ones.
> -
> if (VIR_STRDUP(cpu->model, model->name) < 0 ||
> (model->vendor && VIR_STRDUP(cpu->vendor, model->vendor->name) < 0)) {
> goto cleanup;
Jan
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