On Wed, Jan 02, 2013 at 09:30:20PM +0100, Igor Mammedov wrote: > On Wed, 2 Jan 2013 13:29:10 -0200 > Eduardo Habkost <ehabkost@xxxxxxxxxx> 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 <ehabkost@xxxxxxxxxx> 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. Just like you may end up getting new features enabled by -cpu host after upgrading the kernel, you may end up getting new features enabled by -cpu host after upgrading qemu. If you don't like surprises, don't use -cpu host. ;-) I don't think machine-types exist to avoid user surprise, they exist to keep compatibility (which is not expected to happen when using -cpu host). Keeping compatibility is hard enough in the cases where we really need it, I don't think it is worth the extra work and complexity for an use case where compatibility is not expected. > > > > > > > > > > > > > > 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. The best way I see to simplify kvm_check_features_against_host() requires the feature words array patch, that touches _lots_ of code. I wanted to avoid adding such an intrusive patch as a dependency. > > > > > > > > > > > > > > Signed-off-by: Eduardo Habkost <ehabkost@xxxxxxxxxx> > > > > --- > > > > 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 -- Eduardo -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
