TLB Application note[1] says:
"The TLBs may contain both ordinary and large-page translations for a 4-KByte
range of linear addresses. This may occur if software modifies the paging
structures so that the page size used for the address range changes. If the
two translations differ with respect to page frame or attributes (e.g.,
permissions), processor behavior is undefined and may be implementation
specific. The processor may use a page frame or attributes that correspond to
neither translation; it may improperly set or fail to set the dirty bit in the
appropriate paging-structure entry.
Such undefined behavior is problematic because prefetches and memory accesses
that are a result of speculative execution may occur, using the affected range
of linear addresses. It is also problematic if software (including the software
modifying the paging structures) is accessing data or executing code in the
affected range of linear addresses. Software should not write to a
paging-structure entry in a way that would change, for any linear address,
both the page size and either the page frame or attributes."
Currently we violate this at:
a. kernel identity mapping, where large/small pages setup very early in the
boot will be split up/merged into large pages along with attribute changes
during the direct memory mapping init.
b. while doing cpa(), potentially we will split large page and change attribute
both at the same time.
Following patches fixes this behavior.
[1] http://developer.intel.com/design/processor/applnots/317080.pdf
Signed-off-by: Suresh Siddha <suresh.b.siddha@intel.com>
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v2:
1. Fix the deadlock associated with smp call function and spin_lock_irqsave()
for pgd_lock.
2. No alias checks for __set_pages_np()/__set_pages_p() avoiding the large
text page split from atomic context in CONFIG_DEBUG_PAGEALLOC.
3. Serialize cpa() for !CONFIG_DEBUG_PAGEALLOC, so that a cpu with stale
large page tlb's(but small PTE's in memory) won't do a cpa() in parallel
to some other cpu splitting large pages and changing page attribute for
a small page.
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