[PATCH v4 00/11] KVM: x86: track guest page access

Xiao Guangrong
2016-02-24T09:59:53Z

Changelog in v4:
thanks to Paolo's review, the changes in this version are:
- comment struct kvm_mmu_page_role to explain the rule bits used by indirect
shadow page can not be more than 15 bits
- simplify overflow detection of track count
- remove the wrap functions, kvm_page_track_{add,remove}_page
- rename kvm_slot_page_track_*_nolock to kvm_slot_page_track_*
- rename the function, check_mode, to page_track_mode_is_valid and inline it
- rename kvm_page_track_check_mode to kvm_page_track_is_active
- check if the notifier list is empty before holding the srcu lock
- move the patch adjusting write-flooding more earlier

Changelong in v3:
- refine the code of mmu_need_write_protect() based on Huang Kai's suggestion
- rebase the patchset against current code

Changelog in v2:
- fix a issue that the track memory of memslot is freed if we only move
the memslot or change the flags of memslot
- do not track the gfn which is not mapped in memslots
- introduce the nolock APIs at the begin of the patchset
- use 'unsigned short' as the track counter to reduce the memory and which
should be enough for shadow page table and KVMGT

This patchset introduces the feature which allows us to track page
access in guest. Currently, only write access tracking is implemented
in this version.

Four APIs are introduces:
- kvm_page_track_add_page(kvm, gfn, mode), single guest page @gfn is
added into the track pool of the guest instance represented by @kvm,
@mode specifies which kind of access on the @gfn is tracked

- kvm_page_track_remove_page(kvm, gfn, mode), is the opposed operation
of kvm_page_track_add_page() which removes @gfn from the tracking pool.
gfn is no tracked after its last user is gone

- kvm_page_track_register_notifier(kvm, n), register a notifier so that
the event triggered by page tracking will be received, at that time,
the callback of n->track_write() will be called

- kvm_page_track_unregister_notifier(kvm, n), does the opposed operation
of kvm_page_track_register_notifier(), which unlinks the notifier and
stops receiving the tracked event

The first user of page track is non-leaf shadow page tables as they are
always write protected. It also gains performance improvement because
page track speeds up page fault handler for the tracked pages. The
performance result of kernel building is as followings:

before after
real 461.63 real 455.48
user 4529.55 user 4557.88
sys 1995.39 sys 1922.57

Furthermore, it is the infrastructure of other kind of shadow page table,
such as GPU shadow page table introduced in KVMGT (1) and native nested
IOMMU.

(1): http://lkml.iu.edu/hypermail/linux/kernel/1510.3/01562.html

Xiao Guangrong (11):
KVM: MMU: rename has_wrprotected_page to mmu_gfn_lpage_is_disallowed
KVM: MMU: introduce kvm_mmu_gfn_{allow,disallow}_lpage
KVM: MMU: introduce kvm_mmu_slot_gfn_write_protect
KVM: page track: add the framework of guest page tracking
KVM: page track: introduce kvm_slot_page_track_{add,remove}_page
KVM: MMU: let page fault handler be aware tracked page
KVM: MMU: clear write-flooding on the fast path of tracked page
KVM: page track: add notifier support
KVM: MMU: use page track for non-leaf shadow pages
KVM: MMU: simplify mmu_need_write_protect
KVM: MMU: apply page track notifier

Documentation/virtual/kvm/mmu.txt | 6 +-
arch/x86/include/asm/kvm_host.h | 20 ++-
arch/x86/include/asm/kvm_page_track.h | 61 ++++++++++
arch/x86/kvm/Makefile | 3 +-
arch/x86/kvm/mmu.c | 209 ++++++++++++++++++++++----------
arch/x86/kvm/mmu.h | 5 +
arch/x86/kvm/page_track.c | 222 ++++++++++++++++++++++++++++++++++
arch/x86/kvm/paging_tmpl.h | 5 +
arch/x86/kvm/x86.c | 27 +++--
9 files changed, 479 insertions(+), 79 deletions(-)
create mode 100644 arch/x86/include/asm/kvm_page_track.h
create mode 100644 arch/x86/kvm/page_track.c

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1.8.3.1