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To:     Borislav Petkov <bp@alien8.de>
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Subject: RE: [PATCH Part2 v6 09/49] x86/fault: Add support to handle the RMP
 fault for user address
Thread-Topic: [PATCH Part2 v6 09/49] x86/fault: Add support to handle the RMP
 fault for user address
Thread-Index: AQHYrBDc30zm/ve2UUW13wSedLDd3a2nIMnggADB+gCAAMFX8IAieiDA
Date:   Thu, 1 Sep 2022 20:32:35 +0000
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References: <cover.1655761627.git.ashish.kalra@amd.com>
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[AMD Official Use Only - General]

Hello Boris,

>> It is basically an index into the 4K page within the hugepage mapped=20
>> in the RMP table or in other words an index into the RMP table entry=20
>> 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 fo=
r 2M hugepages.

>Will use pte_index() for 2M pages and pmd_index() for 1G pages.=20

Had a relook into this.=20

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 |=3D (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 a=
s following :=20

static inline size_t pages_per_hpage(int level)
        return page_level_size(level) / PAGE_SIZE;
 }
       =20
static int handle_user_rmp_page_fault(struct pt_regs *regs, unsigned long e=
rror_code,
                                      unsigned long address)
 {     =20
       ...=20
       pfn =3D pte_pfn(*pte);
       =20
        /* 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;
       =20
-               mask =3D pages_per_hpage(level) - pages_per_hpage(level - 1=
);
+              mask =3D pages_per_hpage(level) - 1;
                pfn |=3D (address >> PAGE_SHIFT) & mask;


Thanks,
Ashish