[pok-devel] Re: switch to user space and back during ISR

Hi Philipp,

The design you suggest seems to make sense, I do not foresee any potential issue. Sounds very specific to one arch but on the other hand, this is more a proof-of-concept rather than a clean implementation ... I would suggest to proceed and try and see what is going on when you start to implement it ...

On Mon, Sep 9, 2013 at 9:46 AM, Philipp Eppelt <philipp.eppelt@xxxxxxxxxxxxxxxxxxxxx> wrote:

Hi,

I have two handlers for an ISR which should be invoked during an ISR.
The first handler is the kernel handler which is called fine. Then I
have a handler, which is registered from user space.
To call this handler I first need to switch to the user space
environment. I am doing this by loading the CS,DS,SS and ESP - saved in
the interrupt frame by the interrupt entry. The EIP should point to the
instruction after the following 'iret'.

"pushl %2 \t\n"
"pushl %3 \t\n"
"pushf \t\n"
"pushl %1 \t\n"
"push $1f \t\n"
"iret \t\n"
"1: \t\n"
(with: 2->ss, 3->esp, 1->cs)

This is a snippet from the inline asm block. The code should now be
executed in user space environment. So the handler should be able to use
and modify variables in the user space environment.

Now I need to switch back to the kernel mode to finish the interrupt
service routine and get back to the point of interruption.

Can someone help me out here?

The control flow is as follows:
- irq 0
- irq prolog 0
- isr handler
-- c isr handler
--- kernel handler for irq 0
-- inline asm code to switch to user space
--- user space handler for irq 0
-- inline asm code to switch to kernel space
- isr handler cont'd.
-- update tss
- isr handler cont'd.
- final iret

By now I doubt that design will work, but I haven't come up with a way
to invoke a user space handler and return to the point of interruption, yet..

Any thoughts on this?

Cheers,
Philipp