RE: [Xen-devel] Confused about Xen memory management.

["Nakajima, Jun" <jun.nakajima@xxxxxxxxx>]

There are notions like "guest/pseudo physical" and "machine physical" in
Xen. Guest physical is basically virtualized physical address space, and
that's the one the bulk of the guest kernel code looks at. That way many
assumptions in the kernel are met, thus we can minimize changes to the
kernel when para-virtualizing. Machine physical is real one (i.e. global
and unique), and the guest needs to use machine physical especially for
inter-domain communications or MMU-related hypercalls typically.

The macro pfn_to_mfn() converts guest physical PFN to machine PFN.
So what you need to do is to give the machine address to Xen like:

(pfn_to_mfn(__pa(foo) >> PAGE_SHIFT) << PAGE_SHIFT) + (foo & (PAGE_SIZE
- 1))

Jun
-----Original Message-----
From: xen-devel-admin@xxxxxxxxxxxxxxxxxxxxx
[mailto:xen-devel-admin@xxxxxxxxxxxxxxxxxxxxx] On Behalf Of Rusty
Russell
Sent: Tuesday, February 15, 2005 10:22 PM
To: Xen Mailing List
Subject: [Xen-devel] Confused about Xen memory management.

OK, so I am implementing a prototype where Linux hands an address into
Xen, which gets decremented later (ie. when Xen is executing a different
domain).  It seems that map_domain_mem() is what I want, but how do I
get the physical address of the variable?  virt_to_phys() in Linux
doesn't seem to do the trick, nor virt_to_phys() in Xen.

ie, pseudo code:

linux/mydriver.c:
        static int foo = 1;

        // virt_to_phys(foo) maybe?
        HYPERVISOR_mytest(&foo);

xen/common/test.c:
        int mytest(unsigned long addr)
        {
                // virt_to_phys(addr) maybe?
                manip_later->addr = addr;
                return 0;
        }

        // Some time later
        ...
        int *p = map_domain_mem(manip_later->addr);
        (*p)++;
        unmap_domain_mem(p);

Sorry for the stupid question; I hate VM.
Rusty.
-- 
A bad analogy is like a leaky screwdriver -- Richard Braakman



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