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mm: Cleanup faultaround and finish_fault() codepaths

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alloc_set_pte() has two users with different requirements: in the
faultaround code, it called from an atomic context and PTE page table
has to be preallocated. finish_fault() can sleep and allocate page table
as needed.

PTL locking rules are also strange, hard to follow and overkill for
finish_fault().

Let's untangle the mess. alloc_set_pte() has gone now. All locking is
explicit.

The price is some code duplication to handle huge pages in faultaround
path, but it should be fine, having overall improvement in readability.

Link: https://lore.kernel.org/r/20201229132819.najtavneutnf7ajp@box
Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
[will: s/from from/from/ in comment; spotted by willy]
Signed-off-by: Will Deacon <will@kernel.org>
This commit is contained in:
Kirill A. Shutemov 2020-12-19 15:19:23 +03:00 • committed by Will Deacon
parent 19c329f680
commit f9ce0be71d
5 changed files with 213 additions and 192 deletions
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11
include/linux/pgtable.h
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@ -1314,6 +1314,17 @@ static inline int pmd_trans_unstable(pmd_t *pmd)
#endif
}
/*
* the ordering of these checks is important for pmds with _page_devmap set.
* if we check pmd_trans_unstable() first we will trip the bad_pmd() check
* inside of pmd_none_or_trans_huge_or_clear_bad(). this will end up correctly
* returning 1 but not before it spams dmesg with the pmd_clear_bad() output.
*/
static inline int pmd_devmap_trans_unstable(pmd_t *pmd)
{
return pmd_devmap(*pmd) || pmd_trans_unstable(pmd);
}
#ifndef CONFIG_NUMA_BALANCING
/*
* Technically a PTE can be PROTNONE even when not doing NUMA balancing but