On 19/04/2011 16:44, "david" <david_n@xxxxxx> wrote:
> 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:
xc_translate_foreign_address() will convert a guest virtual address into a
guest physical address. It's not working out for you because guest cr3
values are already guest physical addresses. Thus the virtual-to-physical
conversion you subject the values to is meaningless.
-- Keir
> ----------------------------------------------------------------------
> ...
> ...
> 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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