Re: [RFC PATCH v2 14/32] x86: mm: Provide support to use memblock when spliting large pages

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On Thu, Apr 06, 2017 at 01:37:41PM -0500, Brijesh Singh wrote:
> I did thought about prot idea but ran into another corner case which may require
> us changing the signature of phys_pud_init and phys_pmd_init. The paddr_start
> and paddr_end args into kernel_physical_mapping_init() should be aligned on PMD
> level down (see comment [1]). So, if we encounter a case where our address range
> is part of large page but we need to clear only one entry (i.e asked to clear just
> one page into 2M region). In that case, now we need to pass additional arguments
> into kernel_physical_mapping, phys_pud_init and phys_pmd_init to hint the splitting
> code that it should use our prot for specific entries and all other entries will use
> the old_prot.

Ok, but your !4K case:

+               /*
+                * virtual address is part of large page, create the page
+                * table mapping to use smaller pages (4K). The virtual and
+                * physical address must be aligned to PMD level.
+                */
+               kernel_physical_mapping_init(__pa(vaddr & PMD_MASK),
+                                            __pa((vaddr_end & PMD_MASK) + PMD_SIZE),
+                                            0);


would map a 2M page as encrypted by default. What if we want to map a 2M page
frame as ~_PAGE_ENC?

IOW, if you're adding a new interface, it should be generic enough, like
with prot argument.

-- 
Regards/Gruss,
    Boris.

SUSE Linux GmbH, GF: Felix Imendörffer, Jane Smithard, Graham Norton, HRB 21284 (AG Nürnberg)
-- 



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