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 <address@hidden>
> Signed-off-by: Paolo Bonzini <address@hidden>
> ---
>  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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