Hi Subin: i am not familiar with other architecture, but for ARM, Linux Kernel 2.6.35, i checked the function handle_level_irq()and handle_edge_irq() in chip.c, both of them will call handle_IRQ_event() which is in handle.c. and the function handle_IRQ_event() will call the interrupt handler written by user. Kernel does not open interrupt(ARM CPSR I bit)when calling interrupt handler in handle_IRQ_event() function. this is only for top-half interrupt handling. for bottom-half, it is no doubt that the interrupt will be opened. so if you register a interrupt by request_irq(), the interrupt handler will be called with irq disabled. i tested on Cortex-A9 dual core platform, it is right.
Date: Thu, 23 Feb 2012 11:12:06 -0600 Subject: Re: pagetables used in interrupt context From: subingangadharan@gmail.com To: buyit@live.cn CC: c.a.subramaniam@gmail.com; dhylands@gmail.com; kernelnewbies@kernelnewbies.org
Hi ,
can support nest interrupt if it wants(2.6.35 does not support this). and it is very simple to use the interrupted thread's kernel mode stack as the interrupt context. if kernel use a specific stack which is for interrupt
Thanks for the crystal clear explanation of the page table usage in interrupt context. I have one more doubt, so in 2.6.35 as you said it doesn't support nested interrupt, does it mean that all other interrupts are completely disabled, (I mean no other can interrupt the processor) while executing an interrupt handler.
2012/2/23 卜弋天 <buyit@live.cn>:
Hi :
for ARM architecture, from the point of my view, interrupt can be handled in IRQ, SVC, or SYSTEM modes. 1.if kernel handles interrupt in IRQ mode, it can use separate specific stack of IRQ mode to handle interrupt,but it cannot support nest interupt, suppose you are running interrupt handler in IRQ mode, a new coming interrupt will corrupt the lr_irq which is used for current function. 2. if kernel handles interrupt in SYSTEM mode, the sequences will be : hardware interrupt occurs-->IRQ mode-->SYSTEM mode -->call interrupt handler. kernel can support nest interrupt well by this way, the problem is SYSTEM mode use the same register with USER mode, which means kernel will use the interrupted thread's user mode stack, this will leake information of kernel to user space, so it is not a good idea, although i did this for many years for OMAP chipset(the OS is not linux, it is mixed by REX and my own design.). 3. Linux kernel choose the last one, handle interrupt in SVC mode, which can support nest interrupt if it wants(2.6.35 does not support this). and it is very simple to use the interrupted thread's kernel mode stack as the interrupt context. if kernel use a specific stack which is for interrupt only, the sequences will be : hardware interrupt occurs-->IRQ mode-->SVC mode-->backup sp register of interrupted thread to it's TCB--->set sp register to be the specific kernel stack address-->call interrupt handler--->restore sp of interrupted thread--->return from interrupt. this is a little complicated compared with the current design. so i agree with the current design.
Best Regards
Date: Thu, 23 Feb 2012 08:41:28 -0600
Subject: Re: pagetables used in interrupt context From: c.a.subramaniam@gmail.com To: buyit@live.cn CC: dhylands@gmail.com; subingangadharan@gmail.com; kernelnewbies@kernelnewbies.org
On Thu, Feb 23, 2012 at 6:52 AM, 卜弋天 <buyit@live.cn> wrote:
Hi Subin:
for kernel version 2.6.35, ARM architecture, when interrupt occurs, kernel will change from USER/SVC mode to IRQ mode,backup some registers and change to SVC mode immediately, handle the real interrupt handler in SVC mode, which people say in interrupt context. kernel will use the stack(interrupt context) of interrupted thread to handle the interrupt, and there is no MMU operation which do page table switch. so the thread which is interrupted by interrupt, it's kernel mode stack will be choosed as the interrupt context of current interrupt.
Thanks ! thats a terse explanation! Can you please mention why we do not have a IRQ stack (in terms of size of the stack) to do the processing?
Date: Tue, 21 Feb 2012 19:18:32 -0700 Subject: Re: pagetables used in interrupt context From: subingangadharan@gmail.com To: dhylands@gmail.com CC: kernelnewbies@kernelnewbies.org
Thank you for clearing my doubt.
On Mon, Feb 20, 2012 at 8:39 PM, Dave Hylands <dhylands@gmail.com> wrote:
Hi Subin,
On Mon, Feb 20, 2012 at 6:47 PM, subin gangadharan <subingangadharan@gmail.com> wrote:
Hi All,
Please correct me if I am wrong. In linux each process will have its own page tables, so when a interrupt happens processor will switch to interrupt context and execute the proper handler. So my doubt, if this is the case, interrupt hanlder will be using the pagetables of the interrupted process or is there a separate page table for this.
Yep - that's right. Conceptually you can imagine that the kernel page tables are replicated in each process, so when the interrupt occurs, the kernel mappings will always be in effect regardless of which task is running. How this is actually achieved may vary from architecture to architecture.
-- Dave Hylands Shuswap, BC, Canada http://www.davehylands.com
-- With Regards Subin Gangadharan
I am not afraid and I am also not afraid of being afraid.
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-- With Regards Subin Gangadharan
I am not afraid and I am also not afraid of being afraid.