[AMD Official Use Only - General]

Hello Boris,

quoted

It is basically an index into the 4K page within the hugepage mapped 
in the RMP table or in other words an index into the RMP table entry 
for 4K page(s) corresponding to a hugepage.

So pte_index(address) and for 1G pages, pmd_index(address).

So no reinventing the wheel if we already have helpers for that.

Yes that makes sense and pte_index(address) is exactly what is required for 2M hugepages.

Will use pte_index() for 2M pages and pmd_index() for 1G pages. 

Had a relook into this. 

As I mentioned earlier, this is computing an index into a 4K page within a hugepage mapping,
therefore, though pte_index() works for 2M pages, but pmd_index() will not work for 1G pages.

We basically need to do :
pfn |= (address >> PAGE_SHIFT) & mask;

where mask is the (number of 4K pages per hugepage) - 1

So this still needs the original code but with a fix for mask computation as following : 

static inline size_t pages_per_hpage(int level)
        return page_level_size(level) / PAGE_SIZE;
 }
        
static int handle_user_rmp_page_fault(struct pt_regs *regs, unsigned long error_code,
                                      unsigned long address)
 {      
       ... 
       pfn = pte_pfn(*pte);
        
        /* If its large page then calculte the fault pfn */
        if (level > PG_LEVEL_4K) {
+               /*
+                * index into the 4K page within the hugepage mapping
+                * in the RMP table
+                */
                unsigned long mask;
        
-               mask = pages_per_hpage(level) - pages_per_hpage(level - 1);
+              mask = pages_per_hpage(level) - 1;
                pfn |= (address >> PAGE_SHIFT) & mask;


Thanks,
Ashish