linux-kernel - [PATCH v5 0/4] KVM: async_pf: Fix async pf exception injection

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Message-Id: <1498528021-5115-1-git-send-email-wanpeng.li@hotmail.com>
Date:   Mon, 26 Jun 2017 18:46:57 -0700
From:   Wanpeng Li <kernellwp@...il.com>
To:     linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Cc:     Paolo Bonzini <pbonzini@...hat.com>,
        Radim Krčmář <rkrcmar@...hat.com>,
        Wanpeng Li <wanpeng.li@...mail.com>
Subject: [PATCH v5 0/4] KVM: async_pf: Fix async pf exception injection

 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 almost not touch SVM since I don't have AMD CPU to verify
the modification.

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/api.txt     |  8 +++--
 Documentation/virtual/kvm/msr.txt     |  5 +--
 arch/x86/include/asm/kvm_emulate.h    |  1 +
 arch/x86/include/asm/kvm_host.h       |  7 ++--
 arch/x86/include/uapi/asm/kvm.h       |  3 +-
 arch/x86/include/uapi/asm/kvm_para.h  |  1 +
 arch/x86/kernel/kvm.c                 |  3 +-
 arch/x86/kvm/mmu.c                    |  2 +-
 arch/x86/kvm/svm.c                    |  8 +++--
 arch/x86/kvm/vmx.c                    | 61 +++++++++++++++++++++++++++--------
 arch/x86/kvm/x86.c                    | 28 ++++++++++------
 tools/arch/x86/include/uapi/asm/kvm.h |  3 +-
 12 files changed, 93 insertions(+), 37 deletions(-)

-- 
2.7.4