[Qemu-devel] [PATCH 1/9] target-i386: kvm: -cpu host: Use GET_SUPPORTED_CPUID for SVM features

[Eduardo Habkost <ehabkost@redhat.com>]

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 ec877c7..649cfb2 100644
--- a/target-i386/cpu.c
+++ b/target-i386/cpu.c
@@ -906,13 +906,10 @@ 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