[Qemu-devel] [PATCH 07/17] target-i386: kvm: -cpu host: Use GET_SUPPORTED_CPUID for SVM features

[Andreas Färber]

From: Eduardo Habkost <address@hidden>

The existing -cpu host code simply sets 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 <address@hidden>
Reviewed-by: Gleb Natapov <address@hidden>
Signed-off-by: Andreas Färber <address@hidden>
---
 target-i386/cpu.c |   11 ++++-------
 1 Datei geändert, 4 Zeilen hinzugefügt(+), 7 Zeilen entfernt(-)

diff --git a/target-i386/cpu.c b/target-i386/cpu.c
index 82685dc..1e30015 100644
--- a/target-i386/cpu.c
+++ b/target-i386/cpu.c
@@ -897,13 +897,10 @@ 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 */
 }
 
-- 
1.7.10.4