[AMD Official Use Only - General]
Hello Boris,
>>So essentially we want to map the faulting address to a RMP entry,
>>considering the fact that a 2M host hugepage can be mapped as 4K RMP table entries and 1G host hugepage can be mapped as 2M RMP table entries.
>So something's seriously confusing or missing here because if you fault on a 2M host page and the underlying RMP entries are 4K then you can use pte_index().
>If the host page is 1G and the underlying RMP entries are 2M, pmd_index() should work here too.
>But this piecemeal back'n'forth doesn't seem to resolve this so I'd like to ask you pls to sit down, take your time and give a detailed example of the two possible cases and what the difference is between pte_/pmd_index and your way. Feel free to >add actual debug output and paste it here.
There is 1 64-bit RMP entry for every physical 4k page of DRAM, so essentially every 4K page of DRAM is represented by a RMP entry.
So even if host page is 1G and underlying (smashed/split) RMP entries are 2M, the RMP table entry has to be indexed to a 4K entry
corresponding to that.
If it was simply a 2M entry in the RMP table, then pmd_index() will work correctly.
Considering the following example:
address = 0x40200000;
level = PG_LEVEL_1G;
pfn = 0x40000;
pfn |= pmd_index(address);
This will give the RMP table index as 0x40001.
And it will work if the RMP table entry was simply a 2MB entry, but we need to map this further to its corresponding 4K entry.
With the same example as above:
level = PG_LEVEL_1G;
mask = pages_per_hpage(level) - pages_per_hpage(level - 1);
pfn |= (address >> PAGE_SHIFT) & mask;
This will give the RMP table index as 0x40200.
Which is the correct RMP table entry for a 2MB smashed/split 1G page mapped further to its corresponding 4K entry.
Hopefully this clarifies why pmd_index() can't be used here.
Thanks,
Ashish
