[libvirt] [PATCH qom-cpu 03/11] target-i386: kvm: -cpu host: Use GET_SUPPORTED_CPUID for SVM features

Eduardo Habkost
2013-01-04T22:01:04Z

The existing -cpu host code simply set every bit inside svm_features
(initializing it to -1), and that makes it impossible to make the
enforce/check options work properly when the user asks for SVM features
explicitly in the command-line.

So, instead of initializing svm_features to -1, use GET_SUPPORTED_CPUID
to fill only the bits that are supported by the host (just like we do
for all other CPUID feature words inside kvm_cpu_fill_host()).

This will keep the existing behavior (as filter_features_for_kvm()
already uses GET_SUPPORTED_CPUID to filter svm_features), but will allow
us to properly check for KVM features inside
kvm_check_features_against_host() later.

For example, we will be able to make this:

$ qemu-system-x86_64 -cpu ...,+pfthreshold,enforce

refuse to start if the SVM "pfthreshold" feature is not supported by the
host (after we fix kvm_check_features_against_host() to check SVM flags
as well).

Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>
---
Changes v2:
- Coding style (indentation) fix

Cc: Gleb Natapov <gleb@redhat.com>
Cc: Marcelo Tosatti <mtosatti@redhat.com>
Cc: Joerg Roedel <joro@8bytes.org>
Cc: kvm@vger.kernel.org
---
target-i386/cpu.c | 11 ++++-------
1 file changed, 4 insertions(+), 7 deletions(-)

diff --git a/target-i386/cpu.c b/target-i386/cpu.c
index c83a566..c49a97c 100644
--- a/target-i386/cpu.c
+++ b/target-i386/cpu.c
@@ -908,13 +908,10 @@ static void kvm_cpu_fill_host(x86_def_t *x86_cpu_def)
}
}

- /*
- * Every SVM feature requires emulation support in KVM - so we can't just
- * read the host features here. KVM might even support SVM features not
- * available on the host hardware. Just set all bits and mask out the
- * unsupported ones later.
- */
- x86_cpu_def->svm_features = -1;
+ /* Other KVM-specific feature fields: */
+ x86_cpu_def->svm_features =
+ kvm_arch_get_supported_cpuid(s, 0x8000000A, 0, R_EDX);
+
#endif /* CONFIG_KVM */
}

--
1.7.11.7