qemu-kvm: fix KVMs GET_SUPPORTED_CPUID feature usage

Commit Message

Andre Przywara June 25, 2009, 1:12 p.m. UTC

If we want to trim the user provided CPUID bits for KVM to be not greater
than that of the host, we should
a) not remove the bits _after_ we sent them to the kernel  and
b) not do the bitmangling on the original values while sending a copy
This fixes the masking of features that are not present on the host and
helps to use -cpu host.

Signed-off-by: Andre Przywara <[e-mail]>
---
 qemu-kvm-x86.c |   21 +++++++++++----------
 1 files changed, 11 insertions(+), 10 deletions(-)

Hi,
this is a port of patch 4/6 of my "-cpu host" series for QEMU.
The bug is similar, although the fix is a different one (different files).
Even without "-cpu host" features that the host does not support are
currently _not_ disabled as intended, so I consider this a bugfix.

Regards,
Andre.

Comments

Avi Kivity July 1, 2009, 9:49 a.m. UTC | #1

On 06/25/2009 04:12 PM, Andre Przywara wrote:
> If we want to trim the user provided CPUID bits for KVM to be not greater
> than that of the host, we should
> a) not remove the bits _after_ we sent them to the kernel  and
> b) not do the bitmangling on the original values while sending a copy
> This fixes the masking of features that are not present on the host and
> helps to use -cpu host.
>
>    

Applied, thanks.

Patch

diff --git a/qemu-kvm-x86.c b/qemu-kvm-x86.c
index 66b2b19..f3e4b6b 100644
--- a/qemu-kvm-x86.c
+++ b/qemu-kvm-x86.c
@@ -1190,7 +1190,6 @@  int kvm_arch_qemu_init_env(CPUState *cenv)
 
     qemu_kvm_load_lapic(cenv);
 
-    copy = *cenv;
 
 #ifdef KVM_CPUID_SIGNATURE
     /* Paravirtualization CPUIDs */
@@ -1209,6 +1208,17 @@  int kvm_arch_qemu_init_env(CPUState *cenv)
     pv_ent->eax = get_para_features(kvm_context);
 #endif
 
+    kvm_trim_features(&cenv->cpuid_features,
+                      kvm_arch_get_supported_cpuid(cenv, 1, R_EDX));
+    kvm_trim_features(&cenv->cpuid_ext_features,
+                      kvm_arch_get_supported_cpuid(cenv, 1, R_ECX));
+    kvm_trim_features(&cenv->cpuid_ext2_features,
+                      kvm_arch_get_supported_cpuid(cenv, 0x80000001, R_EDX));
+    kvm_trim_features(&cenv->cpuid_ext3_features,
+                      kvm_arch_get_supported_cpuid(cenv, 0x80000001, R_ECX));
+
+    copy = *cenv;
+
     copy.regs[R_EAX] = 0;
     qemu_kvm_cpuid_on_env(&copy);
     limit = copy.regs[R_EAX];
@@ -1243,15 +1253,6 @@  int kvm_arch_qemu_init_env(CPUState *cenv)
 
     kvm_setup_cpuid2(cenv->kvm_cpu_state.vcpu_ctx, cpuid_nent, cpuid_ent);
 
-    kvm_trim_features(&cenv->cpuid_features,
-                      kvm_arch_get_supported_cpuid(cenv, 1, R_EDX));
-    kvm_trim_features(&cenv->cpuid_ext_features,
-                      kvm_arch_get_supported_cpuid(cenv, 1, R_ECX));
-    kvm_trim_features(&cenv->cpuid_ext2_features,
-                      kvm_arch_get_supported_cpuid(cenv, 0x80000001, R_EDX));
-    kvm_trim_features(&cenv->cpuid_ext3_features,
-                      kvm_arch_get_supported_cpuid(cenv, 0x80000001, R_ECX));
-
     return 0;
 }