linux/arch/powerpc
Aneesh Kumar K.V c777e2a8b6 powerpc/mm: Fix Multi hit ERAT cause by recent THP update
With ppc64 we use the deposited pgtable_t to store the hash pte slot
information. We should not withdraw the deposited pgtable_t without
marking the pmd none. This ensure that low level hash fault handling
will skip this huge pte and we will handle them at upper levels.

Recent change to pmd splitting changed the above in order to handle the
race between pmd split and exit_mmap. The race is explained below.

Consider following race:

		CPU0				CPU1
shrink_page_list()
  add_to_swap()
    split_huge_page_to_list()
      __split_huge_pmd_locked()
        pmdp_huge_clear_flush_notify()
	// pmd_none() == true
					exit_mmap()
					  unmap_vmas()
					    zap_pmd_range()
					      // no action on pmd since pmd_none() == true
	pmd_populate()

As result the THP will not be freed. The leak is detected by check_mm():

	BUG: Bad rss-counter state mm:ffff880058d2e580 idx:1 val:512

The above required us to not mark pmd none during a pmd split.

The fix for ppc is to clear the huge pte of _PAGE_USER, so that low
level fault handling code skip this pte. At higher level we do take ptl
lock. That should serialze us against the pmd split. Once the lock is
acquired we do check the pmd again using pmd_same. That should always
return false for us and hence we should retry the access. We do the
pmd_same check in all case after taking plt with
THP (do_huge_pmd_wp_page, do_huge_pmd_numa_page and
huge_pmd_set_accessed)

Also make sure we wait for irq disable section in other cpus to finish
before flipping a huge pte entry with a regular pmd entry. Code paths
like find_linux_pte_or_hugepte depend on irq disable to get
a stable pte_t pointer. A parallel thp split need to make sure we
don't convert a pmd pte to a regular pmd entry without waiting for the
irq disable section to finish.

Fixes: eef1b3ba05 ("thp: implement split_huge_pmd()")
Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
2016-02-15 21:10:04 +11:00
..
boot powerpc updates for 4.5 2016-01-15 13:18:47 -08:00
configs powerpc/85xx: Enable TWR_P102x in mpc85xx_basic_defconfig 2015-12-22 18:23:21 -06:00
crypto powerpc: Create disable_kernel_{fp,altivec,vsx,spe}() 2015-12-01 13:52:25 +11:00
include powerpc/mm: Fix Multi hit ERAT cause by recent THP update 2016-02-15 21:10:04 +11:00
kernel powerpc/eeh: Fix stale cached primary bus 2016-02-15 21:10:04 +11:00
kvm kvm: rename pfn_t to kvm_pfn_t 2016-01-15 17:56:32 -08:00
lib powerpc: Create disable_kernel_{fp,altivec,vsx,spe}() 2015-12-01 13:52:25 +11:00
math-emu
mm powerpc/mm: Fix Multi hit ERAT cause by recent THP update 2016-02-15 21:10:04 +11:00
net net: filter: make JITs zero A for SKF_AD_ALU_XOR_X 2016-01-06 00:43:52 -05:00
oprofile
perf powerpc/perf: Remove PPMU_HAS_SSLOT flag for Power8 2016-01-28 23:48:35 +11:00
platforms powerpc/powernv: Fix stale PE primary bus 2016-02-15 21:10:04 +11:00
sysdev mm, dax, pmem: introduce pfn_t 2016-01-15 17:56:32 -08:00
xmon powerpc/xmon: Use rtas_call_unlocked() in xmon 2015-12-17 22:40:55 +11:00
Kconfig powerpc/book3s_32: Fix build error with checkpoint restart 2016-01-31 15:08:06 +11:00
Kconfig.debug powerpc updates for 4.5 2016-01-15 13:18:47 -08:00
Makefile
relocs_check.sh