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@@ -778,140 +778,231 @@ valid.
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\end{quote}
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Guest OSes can use the above in place of context switching entire
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LDTs (or the GDT) when the number of changing descriptors is small.
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\section{Context Switching}
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When a guest OS wishes to context switch between two processes,
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it can use the page table and segmentation hypercalls described
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above to perform the the bulk of the privileged work. In addition,
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however, it will need to invoke Xen to switch the kernel (ring 1)
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stack pointer:
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\begin{quote}
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\hypercall{stack\_switch(unsigned long ss, unsigned long esp)}
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Request context switch from hypervisor.
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Request kernel stack switch from hypervisor; {\tt ss} is the new
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stack segement, which {\tt esp} is the new stack pointer.
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\end{quote}
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A final useful hypercall for context switching allows ``lazy''
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save and restore of floating point state:
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\begin{quote}
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\hypercall{fpu\_taskswitch(void)}
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Notify hypervisor that fpu registers needed to be save on context switch.
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This call instructs Xen to set the {\tt TS} bit in the {\tt cr0}
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control register; this means that the next attempt to use floating
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point will cause a trap which the guest OS can trap. Typically it will
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then save/restore the FP state, and clear the {\tt TS} bit.
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\end{quote}
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This is provided as an optimization only; guest OSes can also choose
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to save and restore FP state on all context switches for simplicity.
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\section{Physical Memory Management}
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As mentioned previously, each domain has a maximum and current
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memory allocation. The maximum allocation, set at domain creation
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time, cannot be modified. However a domain can choose to reduce
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and subsequently grow its current allocation by using the
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following call:
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\begin{quote}
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\hypercall{dom\_mem\_op(unsigned int op, unsigned long *extent\_list,
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unsigned long nr\_extents, unsigned int extent\_order)}
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Increase or decrease current memory allocation (as determined by
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the value of {\tt op}). Each invocation provides a list of
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extents each of which is $2^s$ pages in size,
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where $s$ is the value of {\tt extent\_order}.
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\end{quote}
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In addition to simply reducing or increasing the current memory
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allocation via a `balloon driver', this call is also useful for
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obtaining contiguous regions of machine memory when required (e.g.
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for certain PCI devices, or if using superpages).
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\section{Inter-Domain Communication}
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\label{s:idc}
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Xen provides a simple asynchronous notification mechanism via
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\emph{event channels}. Each domain has a set of end-points (or
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\emph{ports}) which may be bound to an event source (e.g. a physical
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IRQ, a virtual IRQ, or an port in another domain). When a pair of
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end-points in two different domains are bound together, then a `send'
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operation on one will cause an event to be received by the destination
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domain.
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\hypercall{event\_channel\_op(void *op)}
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The control and use of event channels involves the following hypercall:
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Inter-domain event-channel management.
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\begin{quote}
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\hypercall{event\_channel\_op(evtchn\_op\_t *op)}
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Inter-domain event-channel management; {\tt op} is a discriminated
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union which allows the following 7 operations:
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\hypercall{grant\_table\_op(unsigned int cmd, void *uop, unsigned int count)}
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\begin{description}
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\item[\it alloc\_unbound:] allocate a free (unbound) local
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port and prepare for connection from a specified domain.
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\item[\it bind\_virq:] bind a local port to a virtual
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IRQ; any particular VIRQ can be bound to at most one port per domain.
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\item[\it bind\_pirq:] bind a local port to a physical IRQ;
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once more, a given pIRQ can be bound to at most one port per
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domain. Furthermore the calling domain must be sufficiently
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privileged.
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\item[\it bind\_interdomain:] construct an interdomain event
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channel; in general, the target domain must have previously allocated
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an unbound port for this channel, although this can be bypassed by
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privileged domains during domain setup.
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\item[\it close:] close an interdomain event channel.
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\item[\it send:] send an event to the remote end of a
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interdomain event channel.
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\item[\it status:] determine the current status of a local port.
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\end{description}
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For more details see
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{\tt xen/include/public/event\_channel.h}.
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\section{Physical Memory Management}
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\hypercall{dom\_mem\_op(unsigned int op, unsigned long *extent\_list,
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unsigned long nr\_extents, unsigned int extent\_order)}
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Increase or decrease memory reservations for guest OS
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\end{quote}
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Event channels are the fundamental communication primitive between
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Xen domains and seamlessly support SMP. However they provide little
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bandwidth for communication {\sl per se}, and hence are typically
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married with a piece of shared memory to produce effective and
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high-performance inter-domain communication.
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Safe sharing of memory pages between guest OSes is carried out granting
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access on a per page basis to individual domains. This is achieved
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by using the {\tt grant\_table\_op()} hypercall.
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%\hypercall{grant\_table\_op(unsigned int cmd, void *uop, unsigned int count)}
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\section{Administrative Operations}
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\label{s:dom0ops}
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A large number of control operations are available to a sufficiently
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privileged domain (typically domain-0). These allow the creation and
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management of new domains, for example. A complete list is given
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below: for more details on any or all of these, please see
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{\tt xen/include/public/dom0\_ops.h}
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\begin{quote}
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\hypercall{dom0\_op(dom0\_op\_t *op)}
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Administrative domain operations for domain management. The options are:
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{\it DOM0\_CREATEDOMAIN}: create new domain, specifying the name and memory usage
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in kilobytes.
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\begin{description}
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\item [\it DOM0\_CREATEDOMAIN:] create a new domain
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{\it DOM0\_CREATEDOMAIN}: create domain
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\item [\it DOM0\_PAUSEDOMAIN:] remove a domain from the scheduler run
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queue.
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{\it DOM0\_PAUSEDOMAIN}: mark domain as unschedulable
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\item [\it DOM0\_UNPAUSEDOMAIN:] mark a paused domain as schedulable
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once again.
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{\it DOM0\_UNPAUSEDOMAIN}: mark domain as schedulable
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\item [\it DOM0\_DESTROYDOMAIN:] deallocate all resources associated
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with a domain
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{\it DOM0\_DESTROYDOMAIN}: deallocate resources associated with the domain
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\item [\it DOM0\_GETMEMLIST:] get list of pages used by the domain
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{\it DOM0\_GETMEMLIST}: get list of pages used by the domain
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\item [\it DOM0\_SCHEDCTL:]
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{\it DOM0\_SCHEDCTL}:
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\item [\it DOM0\_ADJUSTDOM:] adjust scheduling priorities for domain
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{\it DOM0\_ADJUSTDOM}: adjust scheduling priorities for domain
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\item [\it DOM0\_BUILDDOMAIN:] do final guest OS setup for domain
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{\it DOM0\_BUILDDOMAIN}: do final guest OS setup for domain
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\item [\it DOM0\_GETDOMAINFO:] get statistics about the domain
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{\it DOM0\_GETDOMAINFO}: get statistics about the domain
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\item [\it DOM0\_GETPAGEFRAMEINFO:]
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{\it DOM0\_GETPAGEFRAMEINFO}:
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\item [\it DOM0\_GETPAGEFRAMEINFO2:]
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{\it DOM0\_IOPL}: set IO privilege level
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\item [\it DOM0\_IOPL:] set I/O privilege level
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{\it DOM0\_MSR}:
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\item [\it DOM0\_MSR:] read or write model specific registers
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{\it DOM0\_DEBUG}: interactively call pervasive debugger
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\item [\it DOM0\_DEBUG:] interactively invoke the debugger
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{\it DOM0\_SETTIME}: set system time
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\item [\it DOM0\_SETTIME:] set system time
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{\it DOM0\_READCONSOLE}: read console content from hypervisor buffer ring
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\item [\it DOM0\_READCONSOLE:] read console content from hypervisor buffer ring
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{\it DOM0\_PINCPUDOMAIN}: pin domain to a particular CPU
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\item [\it DOM0\_PINCPUDOMAIN:] pin domain to a particular CPU
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{\it DOM0\_GETTBUFS}: get information about the size and location of
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\item [\it DOM0\_GETTBUFS:] get information about the size and location of
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the trace buffers (only on trace-buffer enabled builds)
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{\it DOM0\_PHYSINFO}: get information about the host machine
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\item [\it DOM0\_PHYSINFO:] get information about the host machine
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{\it DOM0\_PCIDEV\_ACCESS}: modify PCI device access permissions
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\item [\it DOM0\_PCIDEV\_ACCESS:] modify PCI device access permissions
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{\it DOM0\_SCHED\_ID}: get the ID of the current Xen scheduler
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\item [\it DOM0\_SCHED\_ID:] get the ID of the current Xen scheduler
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{\it DOM0\_SHADOW\_CONTROL}:
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\item [\it DOM0\_SHADOW\_CONTROL:] switch between shadow page-table modes
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{\it DOM0\_SETDOMAINNAME}: set the name of a domain
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\item [\it DOM0\_SETDOMAININITIALMEM:] set initial memory allocation of a domain
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{\it DOM0\_SETDOMAININITIALMEM}: set initial memory allocation of a domain
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\item [\it DOM0\_SETDOMAINMAXMEM:] set maximum memory allocation of a domain
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{\it DOM0\_SETDOMAINMAXMEM}: set maximum memory allocation of a domain
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{\it DOM0\_GETPAGEFRAMEINFO2}:
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{\it DOM0\_SETDOMAINVMASSIST}: set domain VM assist options
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\item [\it DOM0\_SETDOMAINVMASSIST:] set domain VM assist options
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\end{description}
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\end{quote}
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\section{Miscellaneous Hypercalls}
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\section{Debugging Hypercalls}
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A few additional hypercalls are maintly useful for debugging:
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\begin{quote}
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\hypercall{console\_io(int cmd, int count, char *str)}
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Interact with the console, operations are:
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Use Xen to interact with the console; operations are:
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{\it CONSOLEIO\_write}: Output count characters from buffer str.
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{\it CONSOLEIO\_read}: Input at most count characters into buffer str.
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\end{quote}
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A pair of hypercalls allows access to the underlying debug registers:
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\begin{quote}
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\hypercall{set\_debugreg(int reg, unsigned long value)}
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set debug register reg to value
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Set debug register {\tt reg} to {\tt value}
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\hypercall{get\_debugreg(int reg)}
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get the debug register reg
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Return the contents of the debug register {\tt reg}
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\end{quote}
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And finally, a sometimes useful call is:
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\begin{quote}
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\hypercall{xen\_version(int cmd)}
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Request Xen version number.
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\end{quote}
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