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Re: [Qemu-devel] [PATCH 2/2] target-i386: kvm: enable all supported KVM
From: |
Igor Mammedov |
Subject: |
Re: [Qemu-devel] [PATCH 2/2] target-i386: kvm: enable all supported KVM features for -cpu host |
Date: |
Wed, 2 Jan 2013 21:30:20 +0100 |
On Wed, 2 Jan 2013 13:29:10 -0200
Eduardo Habkost <address@hidden> wrote:
> On Wed, Jan 02, 2013 at 03:52:45PM +0100, Igor Mammedov wrote:
> > On Fri, 28 Dec 2012 16:37:34 -0200
> > Eduardo Habkost <address@hidden> wrote:
> >
> > > When using -cpu host, we don't need to use the kvm_default_features
> > > variable, as the user is explicitly asking QEMU to enable all feature
> > > supported by the host.
> > >
> > > This changes the kvm_cpu_fill_host() code to use GET_SUPPORTED_CPUID to
> > > initialize the kvm_features field, so we get all host KVM features
> > > enabled.
> >
> > 1_2 and 1_3 compat machines diff on pv_eoi flag, with this patch 1_2 might
> > have it set.
> > Is it ok from compat machines pov?
>
> -cpu host is completely dependent on host hardware and kernel version,
> there are no compatibility expectations.
It's still kind of unpleasant surprise if on the same host
"qemu-1.3 -cpu host -machine pc-1.2" and "qemu-1.3+ -cpu host -machine pc-1.2"
would give different pv_eoi feature default, where pv-eoi should be
available after -machine pc-1.2 by default.
>
> >
> > >
> > > This will also allow use to properly check/enforce KVM features inside
> > > kvm_check_features_against_host() later. For example, we will be able to
> > > make this:
> > >
> > > $ qemu-system-x86_64 -cpu ...,+kvm_pv_eoi,enforce
> > >
> > > refuse to start if kvm_pv_eoi is not supported by the host (after we fix
> > > kvm_check_features_against_host() to check KVM flags as well).
> > It would be nice to have kvm_check_features_against_host() patch in this
> > series to verify that this patch and previous patch works as expected.
>
> The kvm_check_features_against_host() change would be a user-visible
> behavior change, and I wanted to keep the changes minimal by now. (the
> main reason I submitted this earlier is to make it easier to clean up
> the init code for CPU subclasses)
>
> I was planning to introduce those behavior changes only after
> introducing the feature-word array, so the kvm_check_features_against_host()
> code can become simpler and easier to review (instead of adding 4
> additional items to the messy struct model_features_t array). But if you
> think we can introduce those changes now, I will be happy to send a
> series that changes that code as well.
It would be better if it and simplifying kvm_check_features_against_host()
were in here together.
>
> >
> > >
> > > Signed-off-by: Eduardo Habkost <address@hidden>
> > > ---
> > > target-i386/cpu.c | 2 ++
> > > 1 file changed, 2 insertions(+)
> > >
> > > diff --git a/target-i386/cpu.c b/target-i386/cpu.c
> > > index 6e2d32d..76f19f0 100644
> > > --- a/target-i386/cpu.c
> > > +++ b/target-i386/cpu.c
> > > @@ -900,6 +900,8 @@ static void kvm_cpu_fill_host(x86_def_t *x86_cpu_def)
> > > /* Other KVM-specific feature fields: */
> > > x86_cpu_def->svm_features =
> > > kvm_arch_get_supported_cpuid(s, 0x8000000A, 0, R_EDX);
> > > + x86_cpu_def->kvm_features =
> > > + kvm_arch_get_supported_cpuid(s, KVM_CPUID_FEATURES, 0,
> > > R_EAX);
> > > #endif /* CONFIG_KVM */
> > > }
> >
>
> --
> Eduardo
>
--
Regards,
Igor