On Thu, Mar 01, 2012 at 07:32:16PM +0900, Takuya Yoshikawa wrote:
> Dropped such mappings when we enabled dirty logging and we will never
> create new ones until we stop the logging.
>
> For this we introduce a new function which can be used to write protect
> a range of PT level pages: although we do not need to care about a range
> of pages at this point, the following patch will need this feature to
> optimize the write protection of many pages.
>
> Signed-off-by: Takuya Yoshikawa <yoshikawa.takuya@xxxxxxxxxxxxx>
> ---
> arch/x86/include/asm/kvm_host.h | 5 ++-
> arch/x86/kvm/mmu.c | 40 +++++++++++++++++++++++++++++---------
> arch/x86/kvm/x86.c | 8 ++----
> 3 files changed, 36 insertions(+), 17 deletions(-)
This is a race with hugetlbfs which is not an issue ATM (it is
hidden by the removal of huge sptes in get_dirty).
guest fault enable dirty logging
tdp_page_fault (all _page_fault functions) kvm_set_memory_region
level = mapping_level(vcpu, gfn)
(finds level == 2 or 3)
rcu_assign_pointer(slot
with
->dirty_bitmap)
synchronize_srcu_expedited()
schedule()
kvm_arch_commit_memory_region()
spin_lock(mmu_lock)
kvm_mmu_slot_remove_write_access()
removes large sptes
spin_unlock(mmu_lock)
spin_lock(mmu_lock)
create large spte accordingly
to level above
spin_unlock(mmu_lock)
Not removing large sptes in get_dirty means this racy sptes could
live from the start of migration to the end of it.
It can be fixed with a preceding patch that checks whether
slot->dirty_bitmap value changes between mapping_level and after
mmu_lock acquision, similarly to mmu_seq. Also please add a
WARN_ON in mmu_set_spte if(slot->dirty_bitmap && level > 1).
And document it clearly.
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