How to find first free entry in PTE

[interruptrequestpack]

Hi all, I'm not really sure if this is a valid question in this forum but how can I find the first free entry in the PTE?

I was looking the volume 3A of intel manuals for some flag, but nothing. Can you help me?

Regards,

irp

[Quoc-Thai_L_Intel]

Hi, I don't have a direct answer for your questions yet. After searching around, I found a couple of threads that could provide some hints for your questions. Here are the two existing threads in this forum:

EPT: Strange VM-Exits

EPT write back memory type and Machine Check exception

-Thai

[interruptrequestpack]

I found out how to do that, thanks anyway!

irp

[Quoc-Thai_L_Intel]

Great,is this something that you can share for other to learn from your finding?
Thanks,
-Thai

[interruptrequestpack]

Yes sure. I will try, because I don't really know this method is correct.

First I check for the pte entry looking for the descriptor entry with PS=0

*pdeB = __CR3_READ(pdeBase);

oldPdeB = *pdeB;

for (*pdeB; *pdeB < MAX_PTE_SIZE; *pdeB++) {

if (pdeB[7] == 0) break;

continue;

}

*pdeB = __CR3_READ(pdeBase); oldPdeB = *pdeB; for (*pdeB; *pdeB < MAX_PTE_SIZE; *pdeB++) { if (pdeB[7] == 0) break; continue; }

Then I just check for the first table entry with preset flag set (it must be one to map a 4kb page)

*pteBase = __SET_PDE(*pdeB);

oldPteBase = *pteBase;

for (*pteBase; *pteBase < MAX_PTE_SIZE; *pteBase++) {

if (pteBase[0] == 1) break;

continue;

}

Maybe I'm missing something, so it that case, help me.

Thanks,

irp

[Quoc-Thai_L_Intel]

Thanks for sharing! You can also check on http://www.xen.org/products/xen_source.htmlfor more ideas.
-Thai