Patchwork [6/9] target-i386: check/enforce: Check SVM flag support as well

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Submitter Eduardo Habkost
Date Jan. 4, 2013, 3:37 p.m.
Message ID <>
Download mbox | patch
Permalink /patch/209481/
State New
Headers show


Eduardo Habkost - Jan. 4, 2013, 3:37 p.m.
When nested SVM is supported, the kernel returns the SVM flag on
GET_SUPPORTED_CPUID[1], so we can check the SVM flag safely on

I don't know why the original code ignored the SVM flag. Maybe it was
because kvm_cpu_fill_host() used the CPUID instruction directly instead

[1] Older kernels (before v2.6.37) returned the SVM flag even if nested
    SVM was _not_ supported. So the only cases where this patch should
    change behavior is when SVM is being requested by the user or the
    CPU model, but not supported by the host. And on these cases we
    really want QEMU to abort if the "enforce" option is set.

Signed-off-by: Eduardo Habkost <>
Cc: Joerg Roedel <>
Cc: Jiri Denemark <>

I'm CCing libvirt people in case having SVM enabled by default may cause
trouble when libvirt starts using the "enforce" flag. I don't know if
libvirt expects most of the QEMU CPU models to have nested SVM enabled.
 target-i386/cpu.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)


diff --git a/target-i386/cpu.c b/target-i386/cpu.c
index 13075c7..21aceed 100644
--- a/target-i386/cpu.c
+++ b/target-i386/cpu.c
@@ -969,7 +969,7 @@  static int kvm_check_features_against_host(x86_def_t *guest_def)
         {&guest_def->ext2_features, &host_def.ext2_features,
             ~0, ext2_feature_name, 0x80000001, R_EDX},
         {&guest_def->ext3_features, &host_def.ext3_features,
-            ~CPUID_EXT3_SVM, ext3_feature_name, 0x80000001, R_ECX}};
+            ~0, ext3_feature_name, 0x80000001, R_ECX}};