On Mon, Mar 10, 2014 at 6:48 PM, Philipp Eppelt <philipp.epp...@mailbox.tu-dresden.de> wrote: > On 03/10/2014 04:24 PM, Youren Shen wrote: >> What make me confused is the relation >> between pok_arch_event_register and pok_meta_handler_init. It seems you >> divided the irq vector to two parts in pok_arch_event_register, Less 32 >> or more than 32. It looks like you have already design some hypercall >> interface. (just like pok_irq_prologue_0 for clock?) But what's >> the meaning of pok_meta_handler_init? I still can't understand it very >> clearly.Could you give me some outline about IRQ handlind in POK which >> invoke this two functions? >> >> If you can provide me a brief overview about the way how you consider >> this Issues and a brief description about your design, it will be >> really helpful to me. > > There are 16 (0 - 15) interrupt lines for hardware interrupts on x86. > If a line is triggered, the PIC will send an interrupt to the CPU. > If interrupts are enabled the CPU will ask for the interrupt number and > looks up this number in the Interrupt Descriptor Table (IDT). > The IDT for HW interrupts looks like this: > 32 | clock ISR (Interrupt Service Routine) > 33 | keyboard ISR > 34 | ... > ... > 47 | ... > > INTEL reserved the first 32 (0-31) IRQ lines, so we start at 32 and go > to 47. 32 corresponds to IRQ line 0, which is the clock interrupt. 33, > is 1 is the keyboard (if I can trust my memory). > > Now the CPU never tells you which IRQ line fires. Therefore, we register > the prologue functions with the IDT, which knows its line number, pushes > it on the stack and calls a general ISR handler. > This general ISR handler checks the line number and calls the handler > registered for this line. Therefore the general ISR handler maintains > its own IDT, a software IDT. > This enables us to register more than one ISR handler function for one > interrupt line. For example, to handle the clock tick in the kernel and > tell the guest system(RTEMS) running in a partition, that a clock tick > occurred (two handlers). > > But, we don't want the POK kernel to wait until the partition handled > the interrupt. So we acknowledge the interrupt with the PIC and then > send the partition the soft-interrupt. And here we go from kernel to > user space and this is the point, where I left of. > > To be more specific in terms of source code. > 'pok_arch_event_register' is called, if you want to register any kind of > interrupt with the IDT. If this happens to be in the hardware interrupt > range [32-47], it registers a prologue handler with the IDT. > > all pok_irq_prologue functions call _ISR_Handler, which in turn calls > _C_isr_handler. This is the general handler, first the asm part and > second the C part. > The _C_isr_handler checks if the kernel has registered a handler for > this IRQ number and calls it. > Then it checks if the current partition has interrupts enabled, if yes, > if there is a handler registered and if the partition isn't already > servicing an earlier interrupt. > If so, the registered handler is invoked. > > If I am talking about 'registered handler' I am talking about the > software IDT the kernel is maintaining. > The software IDT for hardware interrupts is a static table consisting of > 16 entries of the type 'meta_handler'. > 'meta_handler' is a struct consisting of a vector number, and two tables > of the size "kernel + configured number of partitions". > The first table is for function pointers pointing to the > partition's/kernel's hander function, the > what-to-do-if-IRQ-occurrs-function. > The second table flags if the partition is ready for an interrupt. > > So for each interrupt entry in our software-IDT, we get a 'meta_handler' > encapsulating a line number, atables with up to one handler per > partition and a table if the partition is ready for interrupts. > > Next to this software IDT, there is a table 'partition_irq_enabled', > which has one flag per partition and is the software replacement for > CLI/STI. > > 'pok_meta_handler_init' sets up the software-IDT and fills all fields > with start values (magic unused vector number, no handler present, but > waiting) > 'pok_partition_irq_init' sets up partition_irq_enabled table with the > value for disabled (0), so initially no partition gets interrupts until > it asks for them. > > > How can partitions talk to the software-IDT? > POK consists of kernel and partitions. Each partition has a libpok part. > Libpok is the library that enables the partition to talk to other > partitions and the kernel. > An RTEMS guest has a POK partition part (libpart) and the RTEMS part. > Libpart implements the communication with the POK kernel. So when RTEMS > calls some virtualization layer function, the implementation present in > libpart will emit a syscall to the pok kernel and pass along the IRQ > callback function or it just tells to unregister, to > enable/disable/acknowledge interrupts. > Have a look at the virtualization layer functiosn in RTEMS's virtualpok > BSP and examples/rtems-guest/ in POK. > The syscall handling then forwards the request to the e.g. > 'pok_bsp_irq_register_hw'. > > > > I hope that fits into your definition of 'briefly explain'. But it > should give you enough background and explanation to follow the code and > understand the design. > > The really nasty bit happens in the '_C_isr_handler' function in > x86-qemu/bsp.c. > This is explained in my RTLWS'13 paper. Link to paper please.
> In short: Each IRQ entry builds a stack frame, which saves the registers > values on the stack, when the interrupt occurs, so we can continue > execution at the same point. > To handle the IRQ in user space and to return to the point of > interruption, the user space handler needs this data. So the interrupt > frame is copied from the kernel stack to the user stack. Then 'iret' > makes the kernel-space to user-space transition. And that's where we get > a GeneralProtectionFault. > Can we just not use iret from the paravirtualized guest (RTEMS)? This problem reminds me of https://lkml.org/lkml/2011/12/16/460 > Have also a look at the interrupt_middleman function in > rtems-guest/hello.c. This is the user space recovery code of the stack > frame. > > > Cheers, > Philipp > > > > p.s. > This page has a couple of good tutorials for low level OS programming: > http://www.brokenthorn.com/Resources/OSDev15.html > _______________________________________________ > rtems-devel mailing list > rtems-devel@rtems.org > http://www.rtems.org/mailman/listinfo/rtems-devel _______________________________________________ rtems-devel mailing list rtems-devel@rtems.org http://www.rtems.org/mailman/listinfo/rtems-devel
