Messages in this thread | | | Date | Tue, 24 Mar 2020 12:55:52 -0300 | From | Jason Gunthorpe <> | Subject | Re: [PATCH v2] mm/hugetlb: fix a addressing exception caused by huge_pte_offset() |
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On Tue, Mar 24, 2020 at 08:25:09AM -0700, Mike Kravetz wrote: > On 3/24/20 4:55 AM, Jason Gunthorpe wrote: > > Also, since CH moved all the get_user_pages_fast code out of the > > arch's many/all archs can drop their arch specific version of this > > routine. This is really just a specialized version of gup_fast's > > algorithm.. > > > > (also the arch versions seem different, why do some return actual > > ptes, not null?) > > Not sure I understand that last question. The return value should be > a *pte or null.
I mean the common code ends like this:
pmd = pmd_offset(pud, addr); if (sz != PMD_SIZE && pmd_none(*pmd)) return NULL; /* hugepage or swap? */ if (pmd_huge(*pmd) || !pmd_present(*pmd)) return (pte_t *)pmd;
return NULL;
So it always returns a pointer into a PUD or PMD, while say, ppc in __find_linux_pte() ends like:
return pte_offset_kernel(&pmd, ea);
Which is pointing to a PTE
So does sparc:
pmd = pmd_offset(pud, addr); if (pmd_none(*pmd)) return NULL; if (is_hugetlb_pmd(*pmd)) return (pte_t *)pmd; return pte_offset_map(pmd, addr);
Which is even worse because it is leaking a kmap..
etc
> /* > * huge_pte_offset() - Walk the page table to resolve the hugepage > * entry at address @addr > * > * Return: Pointer to page table or swap entry (PUD or PMD) for ^^^^^^^^^^^^^^^^^^^
Ie the above is not followed by the archs
I'm also scratching my head that a function that returns a pte_t * always returns a PUD or PMD. Strange bit of type casting..
Jason
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