On 03/11/2014 01:28 AM, Gedare Bloom wrote: > 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. https://wwwpub.zih.tu-dresden.de/~s8940405/rtlws13_rtems_in_pok_partitions.pdf > >> 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)? With kernel-space and kernel stack, I mean the POK kernel-space and stack. Sorry, I should have made that clear.
This > problem reminds me of https://lkml.org/lkml/2011/12/16/460 Interesting, I'll have a look. > >> 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
