Re: [libvirt] [Qemu-devel] [PATCH qom-cpu 08/11] target-i386: check/enforce: Check SVM flag support as well

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 kvm_check_features_against_host(). 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 of GET_SUPPORTED_CPUID [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 <ehabkost(a)redhat.com&gt;

--- Cc: Joerg Roedel <joro(a)8bytes.org&gt; Cc: kvm(a)vger.kernel.org Cc: libvir-list(a)redhat.com Cc: Jiri Denemark <jdenemar(a)redhat.com&gt; 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. Changes v2: - Coding style fix --- 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 ce64b98..a9dd959 100644 --- a/target-i386/cpu.c +++ b/target-i386/cpu.c @@ -974,7 +974,7 @@ 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} }; assert(kvm_enabled()); -- 1.7.11.7