Messages in this thread | | | Subject | Re: [PATCH 14/15] mm: Align THP mappings for non-DAX | From | William Kucharski <> | Date | Tue, 1 Oct 2019 05:21:26 -0600 |
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> On Oct 1, 2019, at 4:45 AM, Kirill A. Shutemov <kirill@shutemov.name> wrote: > > On Tue, Sep 24, 2019 at 05:52:13PM -0700, Matthew Wilcox wrote: >> >> diff --git a/mm/huge_memory.c b/mm/huge_memory.c >> index cbe7d0619439..670a1780bd2f 100644 >> --- a/mm/huge_memory.c >> +++ b/mm/huge_memory.c >> @@ -563,8 +563,6 @@ unsigned long thp_get_unmapped_area(struct file *filp, unsigned long addr, >> >> if (addr) >> goto out; >> - if (!IS_DAX(filp->f_mapping->host) || !IS_ENABLED(CONFIG_FS_DAX_PMD)) >> - goto out; >> >> addr = __thp_get_unmapped_area(filp, len, off, flags, PMD_SIZE); >> if (addr) > > I think you reducing ASLR without any real indication that THP is relevant > for the VMA. We need to know if any huge page allocation will be > *attempted* for the VMA or the file.
Without a properly aligned address the code will never even attempt allocating a THP.
I don't think rounding an address to one that would be properly aligned to map to a THP if possible is all that detrimental to ASLR and without the ability to pick an aligned address it's rather unlikely anyone would ever map anything to a THP unless they explicitly designate an address with MAP_FIXED.
If you do object to the slight reduction of the ASLR address space, what alternative would you prefer to see?
-- Bill
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