Patchwork [qom-cpu,08/11] target-i386: check/enforce: Check SVM flag support as well

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Submitter Eduardo Habkost
Date Jan. 4, 2013, 10:01 p.m.
Message ID <1357336872-7200-9-git-send-email-ehabkost@redhat.com>
Download mbox | patch
Permalink /patch/209566/
State New
Headers show

Comments

Eduardo Habkost - Jan. 4, 2013, 10:01 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
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@redhat.com>
---
Cc: Joerg Roedel <joro@8bytes.org>
Cc: kvm@vger.kernel.org
Cc: libvir-list@redhat.com
Cc: Jiri Denemark <jdenemar@redhat.com>

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(-)
Gleb Natapov - Jan. 6, 2013, 2:25 p.m.
On Fri, Jan 04, 2013 at 08:01:09PM -0200, Eduardo Habkost wrote:
> 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@redhat.com>
Reviewed-by: Gleb Natapov <gleb@redhat.com>

> ---
> Cc: Joerg Roedel <joro@8bytes.org>
> Cc: kvm@vger.kernel.org
> Cc: libvir-list@redhat.com
> Cc: Jiri Denemark <jdenemar@redhat.com>
> 
> 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
> 

--
			Gleb.

Patch

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());