On 04/18/2011 11:34 AM, Tim Deegan wrote:
At 14:45 +0100 on 15 Apr (1302878734), david wrote:
I'm trying to access the page containing the paging information for a
DomU from Dom0.
I'm doing that by translating the address contained in the DomU CR3
register with xc_translate_foreign_address (libxc) and try to map the
returned frame number with xc_map_foreign_range.
The problem is, that the return value from xc_translate_foreign_address
is 0 (guest cr3 is 0x002f3000 in my case), which indicates an error
(corresponding to the code comments). After some debugging I have
discovered, that pte becomes 0 when level=2 and therefore the function
returns 0 on line 79:
How often does this happen? On every attempt or only from time to time?
Have you checked (say, from inside the guest) that the level-2 PTE isn't
actually zero?
hi,
it happens for every cr3 value. I made some quick and dirty code, which
reads 10 different cr3 values and tries to map the corresponding page:
----------------------------------------------------------------------
...
...
int crfinder = 1;
if(crfinder == 1){
int m;
unsigned long cr3s[10] = {0};
unsigned long mfn = 0;
vcpu_guest_context_any_t *ctxt =
malloc(sizeof(vcpu_guest_context_any_t));
unsigned long cr3 = ctxt->c.ctrlreg[3];
while(1 == 1){
xc_vcpu_getcontext(xcinterface, domain,
dominfo.max_vcpu_id, ctxt);
cr3 = ctxt->c.ctrlreg[3];
for(m = 0; m < 10; m++){
//already stored?
if(cr3s[m] == cr3){
break;
//checked all stored cr3 values?
}else if (cr3s[m] != 0){
continue;
//obviously new one found
}else{
cr3s[m] = cr3;
printf("new cr3 found %08x, stored in
%d\n", cr3, m);
mfn =
xc_translate_foreign_address(xcinterface, domain, 0, cr3s[m]);
printf("calculated mfn %08d for address
%08x\n", mfn, cr3s[m]);
break;
}
}
if(m == 10)
return 0;
}
}
----------------------------------------------------------------------
the corresponding output is:
new cr3 found 002f3000, stored in 0
calculated mfn 00000000 for address 002f3000
new cr3 found 06ac01a0, stored in 1
calculated mfn 00000000 for address 06ac01a0
new cr3 found 06ac0040, stored in 2
calculated mfn 00000000 for address 06ac0040
new cr3 found 06ac00a0, stored in 3
calculated mfn 00000000 for address 06ac00a0
new cr3 found 06ac01e0, stored in 4
calculated mfn 00000000 for address 06ac01e0
new cr3 found 06ac0320, stored in 5
calculated mfn 00000000 for address 06ac0320
new cr3 found 06ac02a0, stored in 6
calculated mfn 00000000 for address 06ac02a0
new cr3 found 06ac01c0, stored in 7
calculated mfn 00000000 for address 06ac01c0
new cr3 found 06ac0200, stored in 8
calculated mfn 00000000 for address 06ac0200
new cr3 found 06ac0060, stored in 9
calculated mfn 00000000 for address 06ac0060
so, every try to translate a cr3 address to a frame number (I don't know
what's the correct wording for frame numbers in hvm domains, .. mfn?)
ends in 0. Maybe it's a failure in my code? I can't find it currently :)
... I'm trying now, to read the cr3 values inside the domain, to check
if the values are the same.
greets,
david
Cheers,
Tim.
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