linux-kernel - Re: [PATCH v7 0/4] KVM: async_pf: Fix async pf exception injection

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Message-ID: <CANRm+Cx6_MRSrcvNgPSzm2dnzMT3Jm00us+-UZqTL1Os6e2z6Q@mail.gmail.com>
Date:   Thu, 29 Jun 2017 15:13:56 +0800
From:   Wanpeng Li <kernellwp@...il.com>
To:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        kvm <kvm@...r.kernel.org>
Cc:     Paolo Bonzini <pbonzini@...hat.com>,
        Radim Krčmář <rkrcmar@...hat.com>,
        Wanpeng Li <wanpeng.li@...mail.com>
Subject: Re: [PATCH v7 0/4] KVM: async_pf: Fix async pf exception injection

2017-06-29 11:01 GMT+08:00 Wanpeng Li <kernellwp@...il.com>:
>  INFO: task gnome-terminal-:1734 blocked for more than 120 seconds.
>        Not tainted 4.12.0-rc4+ #8
>  "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
>  gnome-terminal- D    0  1734   1015 0x00000000
>  Call Trace:
>   __schedule+0x3cd/0xb30
>   schedule+0x40/0x90
>   kvm_async_pf_task_wait+0x1cc/0x270
>   ? __vfs_read+0x37/0x150
>   ? prepare_to_swait+0x22/0x70
>   do_async_page_fault+0x77/0xb0
>   ? do_async_page_fault+0x77/0xb0
>   async_page_fault+0x28/0x30
>
> This is triggered by running both win7 and win2016 on L1 KVM simultaneously,
> and then gives stress to memory on L1, I can observed this hang on L1 when
> at least ~70% swap area is occupied on L0.
>
> This is due to async pf was injected to L2 which should be injected to L1,
> L2 guest starts receiving pagefault w/ bogus %cr2(apf token from the host
> actually), and L1 guest starts accumulating tasks stuck in D state in
> kvm_async_pf_task_wait() since missing PAGE_READY async_pfs.
>
> This patchset fixes it according to Radim's proposal "force a nested VM exit
> from nested_vmx_check_exception if the injected #PF is async_pf and handle
> the #PF VM exit in L1". https://www.spinics.net/lists/kvm/msg142498.html

Note: The patchset depends on commit d4912215d10 ("KVM: nVMX: Fix
exception injection") and commit 9bc1f09f6fa76fd (KVM: async_pf: avoid
async pf injection when in guest mode) on the master branch.

Regards,
Wanpeng Li

>
> v6 -> v7:
>  * drop KVM_GET/PUT_VCPU_EVENTS stuff for nested_apf
>
> v5 -> v6:
>  * move vcpu_svm's apf_reason to vcpu->arch.apf.host_apf_reason
>  * introduce function kvm_handle_page_fault() to be used by both VMX/SVM
>  * introduce svm's codes posted by Paolo
>  * introduce nested_apf
>  * better set MSR_KVM_ASYNC_PF_EN
>
> v4 -> v5:
>  * utilize wrmsr_safe for MSR_KVM_ASYNC_PF_EN
>
> v3 -> v4:
>  * reuse pad field in kvm_vcpu_events for async_page_fault
>  * update kvm_vcpu_events API documentations
>  * change async_page_fault type in vcpu->arch.exception from bool to u8
>
> v2 -> v3:
>  * add the flag to the userspace interface(KVM_GET/PUT_VCPU_EVENTS)
>
> v1 -> v2:
>  * remove nested_vmx_check_exception nr parameter
>  * construct a simple special vm-exit information field for async pf
>  * introduce nested_apf_token to vcpu->arch.apf to avoid change the CR2
>    visible in L2 guest
>  * avoid pass the apf directed towards it (L1) into L2 if there is L3
>    at the moment
>
> Wanpeng Li (4):
>   KVM: x86: Simple kvm_x86_ops->queue_exception parameter
>   KVM: async_pf: Add L1 guest async_pf #PF vmexit handler
>   KVM: async_pf: Force a nested vmexit if the injected #PF is async_pf
>   KVM: async_pf: Let host know whether the guest support delivery async_pf as #PF vmexit
>
>  Documentation/virtual/kvm/msr.txt    |  5 ++--
>  arch/x86/include/asm/kvm_emulate.h   |  1 +
>  arch/x86/include/asm/kvm_host.h      |  8 +++--
>  arch/x86/include/uapi/asm/kvm_para.h |  1 +
>  arch/x86/kernel/kvm.c                |  7 ++++-
>  arch/x86/kvm/mmu.c                   | 35 +++++++++++++++++++++-
>  arch/x86/kvm/mmu.h                   |  2 ++
>  arch/x86/kvm/svm.c                   | 58 ++++++++++++------------------------
>  arch/x86/kvm/vmx.c                   | 39 +++++++++++++++---------
>  arch/x86/kvm/x86.c                   | 19 +++++++-----
>  10 files changed, 108 insertions(+), 67 deletions(-)
>
> --
> 2.7.4
>