Re: [Xen-devel] DomU memory update procedures ?

[Tim Deegan <tim@xxxxxxx>]

Hi, 

At 08:41 -0800 on 06 Jan (1325839315), lmingcsce wrote:
> Hi, I have a question about memory update of DomU. 
> When DomU writes a new value to a memory address, how does hypervisor change
> the value in the particular address and change the dirty page bit? 

The hypervisor is not usually involved in writing the contents of the
memory -- that's just done my the CPU in the normal way.  The same is
true for the dirty bit in the PTE. 

In some cases the hypervisor has to emulate an instruction.  The code
for the emulator is in x86_emulate.c; the pagetable walker is in
arch/x86/mm/guest_walk.c.

> In my current understanding, I find that there is a hypercal do_mmu_update
> in the hypervisor changing the content in the memory.

do_mmu_update() is used by PV domU to change its pagetables; it's not
involved in normal memory writes. 

Cheers,

Tim.

> However, I want to
> know the details about the memory update procedures. Or you can simply tell
> me how can I find this procedures.
> Thanks for your help. 
> 
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