[Qemu-devel] [PATCH uq/master] kvm: always update the MPX model specific register

[Qemu-devel] [PATCH uq/master] kvm: always update the MPX model specific register

[Paolo Bonzini]

The original patch from Liu Jinsong restricted them to reset or full
state updates, but that's unnecessary (and wrong) since the BNDCFGS
MSR has no side effects.

Cc: Liu Jinsong <jinsong.liu@intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
 target-i386/kvm.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/target-i386/kvm.c b/target-i386/kvm.c
index 221c8a0..d34981f 100644
--- a/target-i386/kvm.c
+++ b/target-i386/kvm.c
@@ -1161,6 +1161,9 @@ static int kvm_put_msrs(X86CPU *cpu, int level)
         kvm_msr_entry_set(&msrs[n++], MSR_IA32_MISC_ENABLE,
                           env->msr_ia32_misc_enable);
     }
+    if (has_msr_bndcfgs) {
+        kvm_msr_entry_set(&msrs[n++], MSR_IA32_BNDCFGS, env->msr_bndcfgs);
+    }
 #ifdef TARGET_X86_64
     if (lm_capable_kernel) {
         kvm_msr_entry_set(&msrs[n++], MSR_CSTAR, env->cstar);
@@ -1224,9 +1227,6 @@ static int kvm_put_msrs(X86CPU *cpu, int level)
         if (cpu->hyperv_vapic) {
             kvm_msr_entry_set(&msrs[n++], HV_X64_MSR_APIC_ASSIST_PAGE, 0);
         }
-        if (has_msr_bndcfgs) {
-            kvm_msr_entry_set(&msrs[n++], MSR_IA32_BNDCFGS, env->msr_bndcfgs);
-        }
 
         /* Note: MSR_IA32_FEATURE_CONTROL is written separately, see
          *       kvm_put_msr_feature_control. */
-- 
1.8.3.1

Re: [Qemu-devel] [PATCH uq/master] kvm: always update the MPX model specific register

[Marcelo Tosatti]

On Mon, Jan 20, 2014 at 02:25:36PM +0100, Paolo Bonzini wrote:
> The original patch from Liu Jinsong restricted them to reset or full
> state updates, but that's unnecessary (and wrong) since the BNDCFGS
> MSR has no side effects.

Why is it necessary to save/restore BNDCFGS MSR on states other
than FULL and RESET?

> Cc: Liu Jinsong <jinsong.liu@intel.com>
> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
> ---
>  target-i386/kvm.c | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/target-i386/kvm.c b/target-i386/kvm.c
> index 221c8a0..d34981f 100644
> --- a/target-i386/kvm.c
> +++ b/target-i386/kvm.c
> @@ -1161,6 +1161,9 @@ static int kvm_put_msrs(X86CPU *cpu, int level)
>          kvm_msr_entry_set(&msrs[n++], MSR_IA32_MISC_ENABLE,
>                            env->msr_ia32_misc_enable);
>      }
> +    if (has_msr_bndcfgs) {
> +        kvm_msr_entry_set(&msrs[n++], MSR_IA32_BNDCFGS, env->msr_bndcfgs);
> +    }
>  #ifdef TARGET_X86_64
>      if (lm_capable_kernel) {
>          kvm_msr_entry_set(&msrs[n++], MSR_CSTAR, env->cstar);
> @@ -1224,9 +1227,6 @@ static int kvm_put_msrs(X86CPU *cpu, int level)
>          if (cpu->hyperv_vapic) {
>              kvm_msr_entry_set(&msrs[n++], HV_X64_MSR_APIC_ASSIST_PAGE, 0);
>          }
> -        if (has_msr_bndcfgs) {
> -            kvm_msr_entry_set(&msrs[n++], MSR_IA32_BNDCFGS, env->msr_bndcfgs);
> -        }
>  
>          /* Note: MSR_IA32_FEATURE_CONTROL is written separately, see
>           *       kvm_put_msr_feature_control. */
> -- 
> 1.8.3.1
> 
> --
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Re: [Qemu-devel] [PATCH uq/master] kvm: always update the MPX model specific register

[Paolo Bonzini]

Il 22/01/2014 16:29, Marcelo Tosatti ha scritto:
> > The original patch from Liu Jinsong restricted them to reset or full
> > state updates, but that's unnecessary (and wrong) since the BNDCFGS
> > MSR has no side effects.
>
> Why is it necessary to save/restore BNDCFGS MSR on states other
> than FULL and RESET?

Yes, nothing in QEMU except reset will touch the MSR, but this applies 
also to all the other MSRs that are saved unconditionally.  It's nice to 
be able to poke them with gdb, and saving/restoring the MSR provides that.

Paolo