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 at gmail.com
To: buyit at live.cn
CC: dhylands at gmail.com; subingangadharan at gmail.com; kernelnewbies at kernelnewbies.org

On Thu, Feb 23, 2012 at 6:52 AM, ??? [off-list ref] wrote:

quoted

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?

quoted

quoted

Date: Tue, 21 Feb 2012 19:18:32 -0700
Subject: Re: pagetables used in interrupt context
From: subingangadharan at gmail.com
To: dhylands at gmail.com
CC: kernelnewbies at kernelnewbies.org

quoted

Thank you for clearing my doubt.

On Mon, Feb 20, 2012 at 8:39 PM, Dave Hylands [off-list ref] wrote:

quoted

Hi Subin,

On Mon, Feb 20, 2012 at 6:47 PM, subin gangadharan
[off-list ref] wrote:

quoted

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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