[PATCH v7 00/11] KVM: MMU: fast zap all shadow pages

From: Xiao Guangrong
Date: Wed May 22 2013 - 15:59:24 EST

1): separate some optimization into two patches which do not reuse
the obsolete pages and collapse tlb flushes, suggested by Marcelo.

2): make the patch based on Gleb's diff change which reduce
KVM_REQ_MMU_RELOAD when root page is being zapped.

3): remove calling kvm_mmu_zap_page when patching hypercall, investigated
by Gleb.

4): drop the patch which deleted page from hash list at the "prepare"
time since it can break the walk based on hash list.

5): rename kvm_mmu_invalidate_all_pages to kvm_mmu_invalidate_zap_all_pages.

6): introduce kvm_mmu_prepare_zap_obsolete_page which is used to zap obsolete
page to collapse tlb flushes.

1): reversely walk active_list to skip the new created pages based
on the comments from Gleb and Paolo.

2): completely replace kvm_mmu_zap_all by kvm_mmu_invalidate_all_pages
based on Gleb's comments.

3): improve the parameters of kvm_mmu_invalidate_all_pages based on
Gleb's comments.

4): rename kvm_mmu_invalidate_memslot_pages to kvm_mmu_invalidate_all_pages
5): rename zap_invalid_pages to kvm_zap_obsolete_pages

1): rename is_valid_sp to is_obsolete_sp
2): use lock-break technique to zap all old pages instead of only pages
linked on invalid slot's rmap suggested by Marcelo.
3): trace invalid pages and kvm_mmu_invalidate_memslot_pages()
4): rename kvm_mmu_invalid_memslot_pages to kvm_mmu_invalidate_memslot_pages
according to Takuya's comments.

1): drop unmapping invalid rmap out of mmu-lock and use lock-break technique
instead. Thanks to Gleb's comments.

2): needn't handle invalid-gen pages specially due to page table always
switched by KVM_REQ_MMU_RELOAD. Thanks to Marcelo's comments.

completely redesign the algorithm, please see below.

- do not reset n_requested_mmu_pages and n_max_mmu_pages
- batch free root shadow pages to reduce vcpu notification and mmu-lock
- remove the first patch that introduce kvm->arch.mmu_cache since we only
'memset zero' on hashtable rather than all mmu cache members in this
- remove unnecessary kvm_reload_remote_mmus after kvm_mmu_zap_all

* Issue
The current kvm_mmu_zap_all is really slow - it is holding mmu-lock to
walk and zap all shadow pages one by one, also it need to zap all guest
page's rmap and all shadow page's parent spte list. Particularly, things
become worse if guest uses more memory or vcpus. It is not good for

* Idea
KVM maintains a global mmu invalid generation-number which is stored in
kvm->arch.mmu_valid_gen and every shadow page stores the current global
generation-number into sp->mmu_valid_gen when it is created.

When KVM need zap all shadow pages sptes, it just simply increase the
global generation-number then reload root shadow pages on all vcpus.
Vcpu will create a new shadow page table according to current kvm's
generation-number. It ensures the old pages are not used any more.

Then the invalid-gen pages (sp->mmu_valid_gen != kvm->arch.mmu_valid_gen)
are zapped by using lock-break technique.

Gleb Natapov (1):
KVM: MMU: reduce KVM_REQ_MMU_RELOAD when root page is zapped

Xiao Guangrong (10):
KVM: x86: drop calling kvm_mmu_zap_all in emulator_fix_hypercall
KVM: MMU: drop unnecessary kvm_reload_remote_mmus
KVM: MMU: fast invalidate all pages
KVM: MMU: zap pages in batch
KVM: x86: use the fast way to invalidate all pages
KVM: MMU: show mmu_valid_gen in shadow page related tracepoints
KVM: MMU: add tracepoint for kvm_mmu_invalidate_all_pages
KVM: MMU: do not reuse the obsolete page
KVM: MMU: introduce kvm_mmu_prepare_zap_obsolete_page
KVM: MMU: collapse TLB flushes when zap all pages

arch/x86/include/asm/kvm_host.h | 2 +
arch/x86/kvm/mmu.c | 134 ++++++++++++++++++++++++++++++++++++---
arch/x86/kvm/mmu.h | 1 +
arch/x86/kvm/mmutrace.h | 42 +++++++++---
arch/x86/kvm/x86.c | 16 +----
5 files changed, 162 insertions(+), 33 deletions(-)


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