linux-kernel - [PATCH 0/7] KVM: Alleviate mmu_lock hold time when we start dirty logging

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Date:	Tue, 18 Dec 2012 16:25:58 +0900
From:	Takuya Yoshikawa <yoshikawa_takuya_b1@....ntt.co.jp>
To:	mtosatti@...hat.com, gleb@...hat.com
Cc:	kvm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH 0/7] KVM: Alleviate mmu_lock hold time when we start dirty
 logging

This patch set makes kvm_mmu_slot_remove_write_access() rmap based and
adds conditional rescheduling to it.

The motivation for this change is of course to reduce the mmu_lock hold
time when we start dirty logging for a large memory slot.  You may not
see the problem if you just give 8GB or less of the memory to the guest
with THP enabled on the host -- this is for the worst case.


IMPORTANT NOTE (not about this patch set):

I have hit the following bug many times with the current next branch,
even WITHOUT my patches.  Although I do not know a way to reproduce this
yet, it seems that something was broken around slot->dirty_bitmap.  I am
now investigating the new code in __kvm_set_memory_region().

The bug:
[  575.238063] BUG: unable to handle kernel paging request at 00000002efe83a77
[  575.238185] IP: [<ffffffffa05f9619>] mark_page_dirty_in_slot+0x19/0x20 [kvm]
[  575.238308] PGD 0 
[  575.238343] Oops: 0002 [#1] SMP 

The call trace:
[  575.241207] Call Trace:
[  575.241257]  [<ffffffffa05f96b1>] kvm_write_guest_cached+0x91/0xb0 [kvm]
[  575.241370]  [<ffffffffa0610db9>] kvm_arch_vcpu_ioctl_run+0x1109/0x12c0 [kvm]
[  575.241488]  [<ffffffffa060fd55>] ? kvm_arch_vcpu_ioctl_run+0xa5/0x12c0 [kvm]
[  575.241595]  [<ffffffff81679194>] ? mutex_lock_killable_nested+0x274/0x340
[  575.241706]  [<ffffffffa05faf80>] ? kvm_set_ioapic_irq+0x20/0x20 [kvm]
[  575.241813]  [<ffffffffa05f71c9>] kvm_vcpu_ioctl+0x559/0x670 [kvm]
[  575.241913]  [<ffffffffa05f8a58>] ? kvm_vm_ioctl+0x1b8/0x570 [kvm]
[  575.242007]  [<ffffffff8101b9d3>] ? native_sched_clock+0x13/0x80
[  575.242125]  [<ffffffff8101ba49>] ? sched_clock+0x9/0x10
[  575.242208]  [<ffffffff8109015d>] ? sched_clock_cpu+0xbd/0x110
[  575.242298]  [<ffffffff811a914c>] ? fget_light+0x3c/0x140
[  575.242381]  [<ffffffff8119dfa8>] do_vfs_ioctl+0x98/0x570
[  575.242463]  [<ffffffff811a91b1>] ? fget_light+0xa1/0x140
[  575.246393]  [<ffffffff811a914c>] ? fget_light+0x3c/0x140
[  575.250363]  [<ffffffff8119e511>] sys_ioctl+0x91/0xb0
[  575.254327]  [<ffffffff81684c19>] system_call_fastpath+0x16/0x1b


Takuya Yoshikawa (7):
  KVM: Write protect the updated slot only when we start dirty logging
  KVM: MMU: Remove unused parameter level from __rmap_write_protect()
  KVM: MMU: Make kvm_mmu_slot_remove_write_access() rmap based
  KVM: x86: Remove unused slot_bitmap from kvm_mmu_page
  KVM: Make kvm_mmu_change_mmu_pages() take mmu_lock by itself
  KVM: Make kvm_mmu_slot_remove_write_access() take mmu_lock by itself
  KVM: Conditionally reschedule when kvm_mmu_slot_remove_write_access() takes a long time

 Documentation/virtual/kvm/mmu.txt |    7 ----
 arch/x86/include/asm/kvm_host.h   |    5 ---
 arch/x86/kvm/mmu.c                |   56 +++++++++++++++++++-----------------
 arch/x86/kvm/x86.c                |   13 +++++---
 virt/kvm/kvm_main.c               |    1 -
 5 files changed, 38 insertions(+), 44 deletions(-)

-- 
1.7.5.4

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