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Re: [Qemu-devel] [PATCH 0/7] KVM: MMU: fast write protect
From: |
Paolo Bonzini |
Subject: |
Re: [Qemu-devel] [PATCH 0/7] KVM: MMU: fast write protect |
Date: |
Wed, 3 May 2017 16:57:19 +0200 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.8.0 |
On 03/05/2017 16:50, Xiao Guangrong wrote:
> Furthermore, userspace has no knowledge about if PML is enable (it
> can be required from sysfs, but it is a good way in QEMU), so it is
> difficult for the usespace to know when to use write-protect-all.
> Maybe we can make KVM_CAP_X86_WRITE_PROTECT_ALL_MEM return false if
> PML is enabled?
Yes, that's a good idea. Though it's a pity that, with PML, setting the
dirty bit will still do the massive walk of the rmap. At least with
reset_dirty_pages it's done a little bit at a time.
>> Also, I wonder how the alternative write protection mechanism would
>> affect performance of the dirty page ring buffer patches. You would do
>> the write protection of all memory at the end of
>> kvm_vm_ioctl_reset_dirty_pages. You wouldn't even need a separate
>> ioctl, which is nice. On the other hand, checkpoints would be more
>> frequent and most pages would be write-protected, so it would be more
>> expensive to rebuild the shadow page tables...
>
> Yup, write-protect-all can improve reset_dirty_pages indeed, i will
> apply your idea after reset_dirty_pages is merged.
>
> However, we still prefer to have a separate ioctl for write-protect-all
> which cooperates with KVM_GET_DIRTY_LOG to improve live migration that
> should not always depend on checkpoint.
Ok, I plan to merge the dirty ring pages early in 4.13 development.
Paolo
- [Qemu-devel] [PATCH 0/7] KVM: MMU: fast write protect, guangrong . xiao, 2017/05/03
- [Qemu-devel] [PATCH 1/7] KVM: MMU: correct the behavior of mmu_spte_update_no_track, guangrong . xiao, 2017/05/03
- [Qemu-devel] [PATCH 2/7] KVM: MMU: introduce possible_writable_spte_bitmap, guangrong . xiao, 2017/05/03
- [Qemu-devel] [PATCH 4/7] KVM: MMU: enable KVM_WRITE_PROTECT_ALL_MEM, guangrong . xiao, 2017/05/03
- [Qemu-devel] [PATCH 3/7] KVM: MMU: introduce kvm_mmu_write_protect_all_pages, guangrong . xiao, 2017/05/03
- [Qemu-devel] [PATCH 5/7] KVM: MMU: allow dirty log without write protect, guangrong . xiao, 2017/05/03
- [Qemu-devel] [PATCH 6/7] KVM: MMU: clarify fast_pf_fix_direct_spte, guangrong . xiao, 2017/05/03
- [Qemu-devel] [PATCH 7/7] KVM: MMU: stop using mmu_spte_get_lockless under mmu-lock, guangrong . xiao, 2017/05/03
- Re: [Qemu-devel] [PATCH 0/7] KVM: MMU: fast write protect, Paolo Bonzini, 2017/05/03