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RE: [Xen-devel] Read value of CR3 from DomU VCPU

To: Tim Deegan <Tim.Deegan@xxxxxxxxxx>
Subject: RE: [Xen-devel] Read value of CR3 from DomU VCPU
From: "Nimgaonkar, Satyajeet" <SatyajeetNimgaonkar@xxxxxxxxxx>
Date: Fri, 6 May 2011 16:33:27 +0000
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Thread-topic: [Xen-devel] Read value of CR3 from DomU VCPU
Hi Tim,
           I looked at the xc_translate_foreign_address() in 
tools/libxc/xc_pagetab.c and tried to emulate it. The function below void 
do_jeet1() is a hypercall handler function for my custom hypercall to get the 
value of CR3 from the guest VCPU. But when I try to call this hypercall, my 
machine automatically boots up. Any thoughts?

void do_jeet1(void){   

   unsigned long pgdaddr;
   vcpu_guest_context_u ctx;
   printk ("Successfull Hypercall made to __HYPERVISOR_jeet1\n");   
   pgdaddr = xen_cr3_to_pfn(ctx.nat->ctrlreg[3]);

   printk ("PGDADDR:%lx\n", pgdaddr);



From: Tim Deegan [Tim.Deegan@xxxxxxxxxx]
Sent: Thursday, May 05, 2011 2:33 AM
To: Nimgaonkar, Satyajeet
Cc: xen-devel@xxxxxxxxxxxxxxxxxxx
Subject: Re: [Xen-devel] Read value of CR3 from DomU VCPU

At 21:28 +0100 on 04 May (1304544537), Nimgaonkar, Satyajeet wrote:
> Hi,
>     I intend to map the DomU kernel memory to the Dom0 using the
> function xc_map_foreign_range(). For this I need the machine frame
> number (mfn) for the page I want to map. To get the value of mfn I want
> to read the value of cr3 from the DomU Vcpu data structure i.e. the
> value of ctrlreg[3] from a vcpu_guest_context object.

Look at xc_translate_foreign_address() in tools/libxc/xc_pagetab.c; it
does VA->MFN translations, including extracting CR3.



> Also I have implemented a hypercall and wish to read the cr3 value in the 
> hypercall handler.
> Can anyone share some information regarding how read the cr3 value. Any code 
> examples would help me significantly.
> Thanks a lot.
> Regards,
> Jeet

> _______________________________________________
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> Xen-devel@xxxxxxxxxxxxxxxxxxx
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Tim Deegan <Tim.Deegan@xxxxxxxxxx>
Principal Software Engineer, Xen Platform Team
Citrix Systems UK Ltd.  (Company #02937203, SL9 0BG)

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