Re: [Xen-devel] [PATCH v2 1/4] x86/vvmx: fix virtual interrupt injection when Ack on exit control is used

["Tian, Kevin" <kevin.tian@xxxxxxxxx>]

> From: Roger Pau Monne <roger.pau@xxxxxxxxxx>
> Sent: Monday, February 3, 2020 8:19 PM
> 
> When doing a virtual vmexit (ie: a vmexit handled by the L1 VMM)
> interrupts shouldn't be injected using the virtual interrupt delivery
> mechanism unless the Ack on exit vmexit control bit isn't set in the
> nested vmcs.
> 
> Gate the call to nvmx_update_apicv helper on whether the nested vmcs
> has the Ack on exit bit set in the vmexit control field.
> 
> Note that this fixes the usage of x2APIC by the L1 VMM, at least when
> the L1 VMM is Xen.
> 
> Signed-off-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>

Reviewed-by: Kevin Tian <kevin.tian@xxxxxxxxx>, with a small comment:

> ---
> Changes since v1:
>  - Call nvmx_update_apicv if the "Ack on exit" vmexit control bit
>    isn't set.
> ---
>  xen/arch/x86/hvm/vmx/vvmx.c | 7 ++++++-
>  1 file changed, 6 insertions(+), 1 deletion(-)
> 
> diff --git a/xen/arch/x86/hvm/vmx/vvmx.c b/xen/arch/x86/hvm/vmx/vvmx.c
> index d8ab167d62..3d97a293b2 100644
> --- a/xen/arch/x86/hvm/vmx/vvmx.c
> +++ b/xen/arch/x86/hvm/vmx/vvmx.c
> @@ -1393,7 +1393,12 @@ static void virtual_vmexit(struct cpu_user_regs
> *regs)
>      /* updating host cr0 to sync TS bit */
>      __vmwrite(HOST_CR0, v->arch.hvm.vmx.host_cr0);
> 
> -    if ( cpu_has_vmx_virtual_intr_delivery )
> +    if ( cpu_has_vmx_virtual_intr_delivery &&
> +         /*
> +          * Only inject the vector if the Ack on exit bit is not set, else 
> the
> +          * interrupt will be signaled in the vmcs VM_EXIT_INTR_INFO field.
> +          */
> +         !(get_vvmcs(v, VM_EXIT_CONTROLS) & VM_EXIT_ACK_INTR_ON_EXIT) )

It's a bit odd to put comment between code lines. Can you move it to
the line before 'if'?

>          nvmx_update_apicv(v);
> 
>      nvcpu->nv_vmswitch_in_progress = 0;
> --
> 2.25.0

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