Re: [Xen-devel] [PATCH 5/6] x86/vmx: Defer vmx_vmcs_exit() as long as possible in construct_vmcs()

[Roger Pau Monné <roger.pau@xxxxxxxxxx>]

On Mon, May 28, 2018 at 03:27:57PM +0100, Andrew Cooper wrote:
> paging_update_paging_modes() and vmx_vlapic_msr_changed() both operate on the
> VMCS being constructed.  Avoid dropping and re-acquiring the reference
> multiple times.
> 
> Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
> ---
> CC: Jan Beulich <JBeulich@xxxxxxxx>
> CC: Jun Nakajima <jun.nakajima@xxxxxxxxx>
> CC: Kevin Tian <kevin.tian@xxxxxxxxx>
> CC: Wei Liu <wei.liu2@xxxxxxxxxx>
> CC: Roger Pau Monné <roger.pau@xxxxxxxxxx>
> ---
>  xen/arch/x86/hvm/vmx/vmcs.c | 10 ++++++----
>  1 file changed, 6 insertions(+), 4 deletions(-)
> 
> diff --git a/xen/arch/x86/hvm/vmx/vmcs.c b/xen/arch/x86/hvm/vmx/vmcs.c
> index be02be1..ce78f19 100644
> --- a/xen/arch/x86/hvm/vmx/vmcs.c
> +++ b/xen/arch/x86/hvm/vmx/vmcs.c
> @@ -996,6 +996,7 @@ static int construct_vmcs(struct vcpu *v)
>      struct domain *d = v->domain;
>      u32 vmexit_ctl = vmx_vmexit_control;
>      u32 vmentry_ctl = vmx_vmentry_control;
> +    int rc;
>  
>      vmx_vmcs_enter(v);
>  
> @@ -1083,8 +1084,8 @@ static int construct_vmcs(struct vcpu *v)
>  
>          if ( msr_bitmap == NULL )
>          {
> -            vmx_vmcs_exit(v);
> -            return -ENOMEM;
> +            rc = -ENOMEM;
> +            goto out;
>          }
>  
>          memset(msr_bitmap, ~0, PAGE_SIZE);
> @@ -1258,13 +1259,14 @@ static int construct_vmcs(struct vcpu *v)
>      if ( cpu_has_vmx_tsc_scaling )
>          __vmwrite(TSC_MULTIPLIER, d->arch.hvm_domain.tsc_scaling_ratio);
>  
> -    vmx_vmcs_exit(v);
> -
>      /* will update HOST & GUEST_CR3 as reqd */
>      paging_update_paging_modes(v);
>  
>      vmx_vlapic_msr_changed(v);
>  
> + out:
> +    vmx_vmcs_exit(v);
> +
>      return 0;

Shouldn't you return rc here? Or else you lose the error value.

Roger.

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