Re: [Xen-devel] [RFC v1 12/15] vmx: Properly handle notification event when vCPU is running

["Wu, Feng" <feng.wu@xxxxxxxxx>]

> -----Original Message-----
> From: Zhang, Yang Z
> Sent: Wednesday, March 25, 2015 10:15 PM
> To: Wu, Feng; xen-devel@xxxxxxxxxxxxx
> Cc: JBeulich@xxxxxxxx; keir@xxxxxxx; Tian, Kevin
> Subject: RE: [RFC v1 12/15] vmx: Properly handle notification event when vCPU
> is running
> 
> Wu, Feng wrote on 2015-03-25:
> > When a vCPU is running in Root mode and a notification event has been
> > injected to it. we need to set VCPU_KICK_SOFTIRQ for the current cpu,
> > so the pending interrupt in PIRR will be synced to vIRR before VM-Exit in 
> > time.
> 
> Shouldn't the pending interrupt be synced unconditionally before next vmentry?
> What happens if we didn't set the softirq?

If we didn't set the softirq in the notification handler, the interrupts 
happened exactly
before VM-entry cannot be delivered to guest at this time. Please see the 
following
code fragments from xen/arch/x86/hvm/vmx/entry.S: (pls pay attention to the 
comments)

.Lvmx_do_vmentry

......
                /* If Vt-d engine issues a notification event here,
         * it cannot be delivered to guest during this VM-entry
         * without raising the softirq in notification handler. */

        cmp  %ecx,(%rdx,%rax,1)
        jnz  .Lvmx_process_softirqs

......

        je   .Lvmx_launch

......


.Lvmx_process_softirqs:
        sti
        call do_softirq
        jmp  .Lvmx_do_vmentry

Thanks,
Feng

> 
> >
> > Signed-off-by: Feng Wu <feng.wu@xxxxxxxxx>
> > ---
> >  xen/arch/x86/hvm/vmx/vmx.c        | 24 +++++++++++++++++++++++-
> >  xen/include/asm-x86/hvm/vmx/vmx.h |  1 +
> >  2 files changed, 24 insertions(+), 1 deletion(-)
> > diff --git a/xen/arch/x86/hvm/vmx/vmx.c b/xen/arch/x86/hvm/vmx/vmx.c
> > index b2b4c26..b30392c 100644 --- a/xen/arch/x86/hvm/vmx/vmx.c +++
> > b/xen/arch/x86/hvm/vmx/vmx.c @@ -1838,7 +1838,7 @@ const struct
> > hvm_function_table * __init start_vmx(void)
> >
> >      if ( cpu_has_vmx_posted_intr_processing )
> >      {
> > -        alloc_direct_apic_vector(&posted_intr_vector,
> > event_check_interrupt); +
> > alloc_direct_apic_vector(&posted_intr_vector, +
> > pi_notification_interrupt);
> >
> >          if ( iommu_intpost )
> >              alloc_direct_apic_vector(&pi_wakeup_vector,
> > pi_wakeup_interrupt); @@ -3288,6 +3288,28 @@ void
> > pi_wakeup_interrupt(struct cpu_user_regs *regs)  }
> >
> >  /*
> > + * Handle VT-d posted-interrupt when VCPU is running. + */ + +void
> > pi_notification_interrupt(struct cpu_user_regs *regs) { +    /* +     *
> > We get here because a vCPU is running in Root mode +     * and a
> > notification event has been injected to it. +     * +     * we need to
> > set VCPU_KICK_SOFTIRQ for the current +     * cpu, just like
> > __vmx_deliver_posted_interrupt(). +     * +     * So the pending
> > interrupt in PIRR will be synced to +     * vIRR before VM-Exit in time.
> > +     */ +    set_bit(VCPU_KICK_SOFTIRQ,
> > &softirq_pending(smp_processor_id())); + +    ack_APIC_irq(); +
> > this_cpu(irq_count)++; +} + +/*
> >   * Local variables:
> >   * mode: C
> >   * c-file-style: "BSD"
> > diff --git a/xen/include/asm-x86/hvm/vmx/vmx.h
> > b/xen/include/asm-x86/hvm/vmx/vmx.h index f4296ab..e53275b 100644 ---
> > a/xen/include/asm-x86/hvm/vmx/vmx.h +++
> > b/xen/include/asm-x86/hvm/vmx/vmx.h @@ -576,6 +576,7 @@ void
> > free_p2m_hap_data(struct p2m_domain *p2m); void
> p2m_init_hap_data(struct
> > p2m_domain *p2m);
> >
> >  void pi_wakeup_interrupt(struct cpu_user_regs *regs);
> > +void pi_notification_interrupt(struct cpu_user_regs *regs);
> >
> >  /* EPT violation qualifications definitions */
> >  #define _EPT_READ_VIOLATION         0
> 
> 
> Best regards,
> Yang
> 


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