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* Memory Mapping
@ 2011-05-06 14:50 Lakshitha Harshan
  2011-05-06 15:31 ` Konrad Rzeszutek Wilk
  0 siblings, 1 reply; 10+ messages in thread
From: Lakshitha Harshan @ 2011-05-06 14:50 UTC (permalink / raw)
  To: xen-devel


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Hi all,

I want to get the access to task structs in domUs to get the memory
addresses of code segments in each process. So how do I read/map the data
correctly which I get through xc_map_foreign_range or  xc_map_foreign_batch?

Thanks,
Harshan

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^ permalink raw reply	[flat|nested] 10+ messages in thread
* Memory mapping
@ 2009-02-16 16:58 Frederic Beck
  2009-02-18 14:35 ` Frederic Beck
  0 siblings, 1 reply; 10+ messages in thread
From: Frederic Beck @ 2009-02-16 16:58 UTC (permalink / raw)
  To: xen-devel

Hello

I managed to do what i wanted with my module (finally gave up on the
syscall and did everything in the module init), and i foudn the offsets
i was looking for. I later found out that what i've done was already
available via XenAccess (tools/linux-offset-finder).

I have the following offsets:
linux_name = 0x225;
linux_tasks = 0xd0;
linux_mm = 0xe8;
linux_pid = 0x10c;
linux_pgd = 0x24;
linux_addr = 0x84;

After disabling fast system calls handling, i modified  do_guest_trap in
xen/arch/x86/traps.c. I get the user regs to have access to the CPU
registers EAX, EIP and ESP (info i wanna log via the tracing). I take
the ESP and apply the mask 0xFFFFF000 to get the base address of the
thread_info struct.

user_regs = guest_cpu_user_regs();
base_addr = (user_regs->esp & 0xFFFFF000);

Then the first 4 bytes after this base_addr are on a regular system a
pointer to a task_struct where the PId of the current task is stored,
which i wanna get. On a regular OS (i tested on Dom0 or DomU) I can
find easily the PID and print it out. I would like to do the same in
the hypervisor. 

I tried to map the same code without modification, but i begin reading
memory addresses that do not exist and the hypervisor crashes when i
create my DomU. So far, i'm not very surprised, as there must be some
virtual memory handling that i'm missing.

However, i do not understand well how i can do the mapping. how do i
map this kernel address in the hypervisor to read the right memory
address ?

I guess that this mapping will be different for HVM and PV domains ? Is
there a function that dynamically detects what kind of domain the guest
is ?

Moreover, i found out in XenAccess that the right formula to get the
PID would be 
memcpy(&pid, memory + offset + PID_OFFSET - TASKS_OFFSET,4);
I guess that memory is the base adress of the virtual stack. How can i
find that value ? in that case the base_addr i calculated earlier would
be the offset ?

Thanks for the help!

Regards
Fred

^ permalink raw reply	[flat|nested] 10+ messages in thread
* RE: Xeno-unstable crashing at boot
@ 2005-05-16 19:55 Ian Pratt
  2005-05-17 11:52 ` Mike Wray
  0 siblings, 1 reply; 10+ messages in thread
From: Ian Pratt @ 2005-05-16 19:55 UTC (permalink / raw)
  To: Mike Wray; +Cc: xen-devel

 > > What hardware is the problem machine? It has an impresively 
> long list of
> > ACPI table entries. Since the code being executed is the 
> native Linux
> > code it's surprising that it's having problems. 
> 
> It's a dual processor 2.8GHz xeon, 2GB RAM.
> The cpuinfo was attached to an earlier email.
> I've attached it again, with hwconf.

No, I mean the make and model of the machine. I have 3 different kinds
of dual 2.8GHz Xeon with tg3 NICs that Xen unstable works fine with. It
something specific to your particular machine, probably the BIOS. (BTW:
are their BIOS upgrades available?)

> > Please can you try using a DEBUG=y build of Xen, and then adding
> > show_guest_stack earlier in the failure path.
> 
> So 'DEBUG=y make world'?

"make clean; make debug=y dist" should do it.

> Can you suggest what a good place 'earlier in the failure 
> path' might be?

I expect you'll get an error message from Xen before the BUG in domain
crash. See where the error message comes from, and then add the
show_guest_stack to the appropriate path.

Thanks,
Ian

^ permalink raw reply	[flat|nested] 10+ messages in thread
* memory mapping
@ 2004-12-17  4:54 Srividya Ramanathan
  0 siblings, 0 replies; 10+ messages in thread
From: Srividya Ramanathan @ 2004-12-17  4:54 UTC (permalink / raw)
  To: linux-mips

Hi,
 Thanks a lot. I am facing one more problem. There is
one section of the driver where we map a small portion
of the PCI card's memory into user space. During
driver initialization, a magic number is written into
this space and read back from user space to verify the
driver is set up correctly. This fails.

any other way to locate the problem?

Thanks
R Srividya



		
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^ permalink raw reply	[flat|nested] 10+ messages in thread
* RE: Memory mapping
@ 2001-11-20 15:32 Siders, Keith
  0 siblings, 0 replies; 10+ messages in thread
From: Siders, Keith @ 2001-11-20 15:32 UTC (permalink / raw)
  To: 'Keith Owens'; +Cc: Linux-Mips (E-mail)

-> >OK, now that I've spent a couple weeks looking at Linux 
-> >memory management,
-> >can someone please help me straighten this out. First, I 
-> >have a requirement
-> >to "unobtrusively" hot-patch instruction code ( and 
-> >probably data also )
-> >segments in memory.
-> 
-> At the risk of stating the obvious, have you looked at the 
-> ptrace code
-> in arch/$(ARCH)/kernel/ptrace.c?  That already does all the work for
-> reading and writing code and data.
->

Yep, most of what it does I have in the simple patch case: replace existing
instructions. It did give me some things to check to make certain it works,
though. Thanks. The other case requires adding code, so kernel space memory
must be allocated and mmap'd. That's what I've been wrestling most with.

^ permalink raw reply	[flat|nested] 10+ messages in thread
* Memory mapping
@ 2001-11-19 16:18 Siders, Keith
  2001-11-20  0:15 ` Keith Owens
  0 siblings, 1 reply; 10+ messages in thread
From: Siders, Keith @ 2001-11-19 16:18 UTC (permalink / raw)
  To: Linux-Mips (E-mail)

OK, now that I've spent a couple weeks looking at Linux memory management,
can someone please help me straighten this out. First, I have a requirement
to "unobtrusively" hot-patch instruction code ( and probably data also )
segments in memory. I've decided that the best way to do this is to mmap
device memory of a pseudo-device module to both the patching process and the
target process. To the patching process it can be viewed as just RW data
memory, but to the target process it must look like read-only executable. In
addition I have found the find_task_by_pid() for getting the process
descriptor for the target process. So...

1. Can I copy off the current task pointer and substitute the task pointer
returned by find_task_by_pid() (in the pseudo-device mmap() call), and do
remap_page_range() to map the memory to the target process?

2. Do I need to set task->has_cpu or any other controls to have the remap
work?

3. The book "Understanding the Linux Kernel" has so many references to
vm_area_struct that I'm confused as to when this memory area gets allocated,
let alone who it belongs to in the mmap() call. I had thought I'd just do
get_free_page() and mmap that address, but everything seems very convoluted
with so many references in the API's to vm_area_struct: I can't seem to keep
straight just what VM is supposed to be passed in the mmap() call, where it
comes from, etc. Is this the [task]->active_mm->mmap vm_area_struct or
should I look for another? 

HELP! Code deadline was supposed to be noon today ( I'm screwed ) and this
is the main hitch holding me back. BTW, I can't tell why I'm doing this, so
please don't ask...

Keith Siders
Software Engineer
 Toshiba America Consumer Products, Inc.
Advanced Television Technology Center
801 Royal Parkway, Suite 100
Nashville, Tennessee 37214
Phone: (615) 257-4050
Fax:   (615) 453-7880

^ permalink raw reply	[flat|nested] 10+ messages in thread
end of thread, other threads:[~2011-05-06 15:31 UTC | newest]

Thread overview: 10+ messages (download: mbox.gz follow: Atom feed
-- links below jump to the message on this page --
2011-05-06 14:50 Memory Mapping Lakshitha Harshan
2011-05-06 15:31 ` Konrad Rzeszutek Wilk
  -- strict thread matches above, loose matches on Subject: below --
2009-02-16 16:58 Memory mapping Frederic Beck
2009-02-18 14:35 ` Frederic Beck
2005-05-16 19:55 Xeno-unstable crashing at boot Ian Pratt
2005-05-17 11:52 ` Mike Wray
2005-05-17 13:26   ` Keir Fraser
2005-05-17 16:01     ` memory mapping Grzegorz Milos
2005-05-17 16:09       ` Grzegorz Milos
2004-12-17  4:54 Srividya Ramanathan
2001-11-20 15:32 Memory mapping Siders, Keith
2001-11-19 16:18 Siders, Keith
2001-11-20  0:15 ` Keith Owens

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