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[Xen-devel] GDT access from DOM-0 driver

  • To: "Ian Pratt" <m+Ian.Pratt@xxxxxxxxxxxx>, "Xen devel list" <xen-devel@xxxxxxxxxxxxxxxxxxx>
  • From: "Kaushik Barde" <Kaushik_Barde@xxxxxxxxxxx>
  • Date: Fri, 9 Feb 2007 23:52:26 -0800
  • Delivery-date: Fri, 09 Feb 2007 23:52:21 -0800
  • List-id: Xen developer discussion <xen-devel.lists.xensource.com>
  • Thread-index: AcdG/Nc6FhN5E7LwEduJCgAX8io7RQAASYugAHRDoLABBIU+4A==
  • Thread-topic: GDT access from DOM-0 driver

Now I could get the EPS signature, However, we store some information
about disk configuration options (HP/HPA) in unused area of GDT.

Driver has physical memory read and write functions.
These physical memory read / write functions have following assumptions:

- Depending on the source physical address, we either use ioremap to map
the page(s) in, or use phys_to_virt.  
- If the physical address has already been mapped by the kernel we can
just use phys_to_virt.
- If the address is not mapped, only up to one page size is copied, in
an effort to reduce virtual address space usage.
In this per your suggestion, because DOM0 RAM is already remapped,

The virt_to_bus() or bus_to_virt()  are replaced by
But what about phys_to_virt(), does driver need to change them to
pseudo-physical address functions?



-----Original Message-----
From: xen-devel-bounces@xxxxxxxxxxxxxxxxxxx
[mailto:xen-devel-bounces@xxxxxxxxxxxxxxxxxxx] On Behalf Of Ian Pratt
Sent: Sunday, February 04, 2007 6:53 PM
To: Kaushik Barde; Xen devel list
Subject: RE: [Xen-devel] EPS Signature 

> We want to access the EBDA Entry Point Signature at 40:0E for our
> through a driver,
> We noticed that driver is trying to read from a pseudo physical
> and not the physical machine RAM location. Hence it's not getting the
> proper value. But if we have to read from the machine RAM location we
> use ( virt_to_bus or bus_to_virt) per dev_list comments.
> But this area is under the control of hypervisor. I do not know if we
> ioremap these pages ( those which belong to hypervisor).
> I am trying to see if we can be able to get to the 40:0E address. And
> the correct EPS signature

Dom0 already has the bottom 1MB of physical ram mapped. You can use the
poorly named isa_bus_to_virt()


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