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: Friday, March 27, 2015 12:44 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 2015-03-27:
> >
> >
> > Zhang, Yang Z wrote on 2015-03-25:
> >> 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
> 
> You are right! This helps me to recall why raise the softirq when delivering 
> the
> PI.

Yes, __vmx_deliver_posted_interrupt() is the software way to deliver PI, it 
sets the
softirq for this purpose, however, when VT-d HW delivers PI, we have no control 
to
the HW itself, hence we need to set this softirq in the Notification Event 
handler.

Thanks,
Feng

> 
> > 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
> >>
> 
> 
> Best regards,
> Yang
> 


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