Re: [Xen-devel] [PATCH v2 01/10] x86/HVM: Introduce struct hvm_pi_ops

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 31.12.16 at 06:45, <suravee.suthikulpanit@xxxxxxx> wrote:
> --- a/xen/include/asm-x86/hvm/domain.h
> +++ b/xen/include/asm-x86/hvm/domain.h
> @@ -72,6 +72,67 @@ struct hvm_ioreq_server {
>      bool_t                 bufioreq_atomic;
>  };
>  
> +struct hvm_pi_ops {
> +    /*
> +     * To handle posted interrupts correctly, we need to set the following
> +     * state:
> +     *
> +     * * The PI notification vector (NV)
> +     * * The PI notification destination processor (NDST)
> +     * * The PI "suppress notification" bit (SN)
> +     * * The vcpu pi "blocked" list
> +     *
> +     * If a VM is currently running, we want the PI delivered to the guest 
> vcpu
> +     * on the proper pcpu (NDST = v->processor, SN clear).
> +     *
> +     * If the vm is blocked, we want the PI delivered to Xen so that it can
> +     * wake it up  (SN clear, NV = pi_wakeup_vector, vcpu on block list).
> +     *
> +     * If the VM is currently either preempted or offline (i.e., not running
> +     * because of some reason other than blocking waiting for an interrupt),
> +     * there's nothing Xen can do -- we want the interrupt pending bit set in
> +     * the guest, but we don't want to bother Xen with an interrupt (SN 
> clear).
> +     *
> +     * There's a brief window of time between vmx_intr_assist() and checking
> +     * softirqs where if an interrupt comes in it may be lost; so we need Xen
> +     * to get an interrupt and raise a softirq so that it will go through the
> +     * vmx_intr_assist() path again (SN clear, NV = posted_interrupt).
> +     *
> +     * The way we implement this now is by looking at what needs to happen on
> +     * the following runstate transitions:
> +     *
> +     * A: runnable -> running
> +     *  - SN = 0
> +     *  - NDST = v->processor
> +     * B: running -> runnable
> +     *  - SN = 1
> +     * C: running -> blocked
> +     *  - NV = pi_wakeup_vector
> +     *  - Add vcpu to blocked list
> +     * D: blocked -> runnable
> +     *  - NV = posted_intr_vector
> +     *  - Take vcpu off blocked list
> +     *
> +     * For transitions A and B, we add hooks into vmx_ctxt_switch_{from,to}
> +     * paths.
> +     *
> +     * For transition C, we add a new arch hook, arch_vcpu_block(), which is
> +     * called from vcpu_block() and vcpu_do_poll().
> +     *
> +     * For transition D, rather than add an extra arch hook on vcpu_wake, we
> +     * add a hook on the vmentry path which checks to see if either of the 
> two
> +     * actions need to be taken.
> +     *
> +     * These hooks only need to be called when the domain in question 
> actually
> +     * has a physical device assigned to it, so we set and clear the 
> callbacks
> +     * as appropriate when device assignment changes.
> +     */
> +    void (*vcpu_block) (struct vcpu *);
> +    void (*pi_switch_from) (struct vcpu *v);
> +    void (*pi_switch_to) (struct vcpu *v);
> +    void (*pi_do_resume) (struct vcpu *v);
> +};

While the hooks (as said, with the pi_ prefixes dropped) are
certainly fine to move here, the comment is extremely VMX
centric, and hence doesn't fit in this file. It either needs to be
generalized, or it should remain in VMX specific code, perhaps
with a referral to it added here.

Jan


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