typedef struct vcpu_info {
/*
* 'evtchn_upcall_pending' is written non-zero by Xen to indicate
* a pending notification for a particular VCPU. It is then cleared
* by the guest OS /before/ checking for pending work, thus avoiding
* a set-and-check race. Note that the mask is only accessed by Xen
* on the CPU that is currently hosting the VCPU. This means that the
* pending and mask flags can be updated by the guest without special
* synchronisation (i.e., no need for the x86 LOCK prefix).
* This may seem suboptimal because if the pending flag is set by
* a different CPU then an IPI may be scheduled even when the mask
* is set. However, note:
* 1. The task of 'interrupt holdoff' is covered by the per-event-
* channel mask bits. A 'noisy' event that is continually being
* triggered can be masked at source at this very precise
* granularity.
* 2. The main purpose of the per-VCPU mask is therefore to restrict
* reentrant execution: whether for concurrency control, or to
* prevent unbounded stack usage. Whatever the purpose, we expect
* that the mask will be asserted only for short periods at a time,
* and so the likelihood of a 'spurious' IPI is suitably small.
* The mask is read before making an event upcall to the guest: a
* non-zero mask therefore guarantees that the VCPU will not receive
* an upcall activation. The mask is cleared when the VCPU requests
* to block: this avoids wakeup-waiting races.
*/
uint8_t evtchn_upcall_pending;
uint8_t evtchn_upcall_mask;
unsigned long evtchn_pending_sel;
arch_vcpu_info_t arch;
vcpu_time_info_t time;
} vcpu_info_t; /* 64 bytes (x86) */
- evtchn_upcall_pending
- This is set non-zero by Xen to indicate
that there are pending events to be received.
- evtchn_upcall_mask
- This is set non-zero to disable all
interrupts for this CPU for short periods of time. If individual
event channels need to be masked, the evtchn_mask in the shared_info_t is used instead.
- evtchn_pending_sel
- When an event is delivered to this VCPU, a
bit is set in this selector to indicate which word of the evtchn_pending array in the shared_info_t contains the
event in question.
- arch
- Architecture-specific VCPU info. On x86 this contains the
virtualized CR2 register (page fault linear address) for this VCPU.
- time
- Time values for this VCPU.
