Re: [Xen-devel] [PATCH v5 08/17] vmx: Suppress posting interrupts when 'SN' is set

[Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>]

On Wed, Aug 12, 2015 at 10:35:29AM +0800, Feng Wu wrote:
> Currently, we don't support urgent interrupt, all interrupts
> are recognized as non-urgent interrupt, so we cannot send
> posted-interrupt when 'SN' is set.
> 
> CC: Kevin Tian <kevin.tian@xxxxxxxxx>
> CC: Keir Fraser <keir@xxxxxxx>
> CC: Jan Beulich <jbeulich@xxxxxxxx>
> CC: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
> Signed-off-by: Feng Wu <feng.wu@xxxxxxxxx>
> ---
> v5:
> - keep the vcpu_kick() at the end of vmx_deliver_posted_intr()
> - Keep the 'return' after calling __vmx_deliver_posted_interrupt()
> 
> v4:
> - Coding style.
> - V3 removes a vcpu_kick() from the eoi_exitmap_changed path
>   incorrectly, fix it.
> 
> v3:
> - use cmpxchg to test SN/ON and set ON
> 
>  xen/arch/x86/hvm/vmx/vmx.c | 29 ++++++++++++++++++++++++++++-
>  1 file changed, 28 insertions(+), 1 deletion(-)
> 
> diff --git a/xen/arch/x86/hvm/vmx/vmx.c b/xen/arch/x86/hvm/vmx/vmx.c
> index c32d863..d2a4cfb 100644
> --- a/xen/arch/x86/hvm/vmx/vmx.c
> +++ b/xen/arch/x86/hvm/vmx/vmx.c
> @@ -1701,8 +1701,35 @@ static void vmx_deliver_posted_intr(struct vcpu *v, u8 
> vector)
>           */
>          pi_set_on(&v->arch.hvm_vmx.pi_desc);
>      }
> -    else if ( !pi_test_and_set_on(&v->arch.hvm_vmx.pi_desc) )
> +    else
>      {
> +        struct pi_desc old, new, prev;
> +

Could you add a comment saying:

/* To skip over first check in the loop below. */

just to easy somebody in reading the code.
> +        prev.control = 0;
> +
> +        do {
> +            /*
> +             * Currently, we don't support urgent interrupt, all
> +             * interrupts are recognized as non-urgent interrupt,
> +             * so we cannot send posted-interrupt when 'SN' is set.
> +             * Besides that, if 'ON' is already set, we cannot set
> +             * posted-interrupts as well.
> +             */
> +            if ( pi_test_sn(&prev) || pi_test_on(&prev) )
> +            {
> +                vcpu_kick(v);
> +                return;
> +            }
> +
> +            old.control = v->arch.hvm_vmx.pi_desc.control &
> +                          ~( 1 << POSTED_INTR_ON | 1 << POSTED_INTR_SN );
> +            new.control = v->arch.hvm_vmx.pi_desc.control |
> +                          1 << POSTED_INTR_ON;
> +
> +            prev.control = cmpxchg(&v->arch.hvm_vmx.pi_desc.control,
> +                                   old.control, new.control);
> +        } while ( prev.control != old.control );
> +
>          __vmx_deliver_posted_interrupt(v);
>          return;
>      }

Otherwise:

Reviewed-by: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
> -- 
> 2.1.0
> 
> 
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