[Bug 216388] On Host, kernel errors in KVM, on guests, it shows CPU stalls

[bugzilla-daemon@kernel.org]

https://bugzilla.kernel.org/show_bug.cgi?id=216388

--- Comment #1 from Sean Christopherson (seanjc@google.com) ---
+GVT folks

On Sun, Aug 21, 2022, bugzilla-daemon@kernel.org wrote:
> https://bugzilla.kernel.org/show_bug.cgi?id=216388
> 
>             Bug ID: 216388
>            Summary: On Host, kernel errors in KVM, on guests, it shows CPU
>                     stalls
>            Product: Virtualization
>            Version: unspecified
>     Kernel Version: 5.19.0 / 5.19.1 / 5.19.2
>           Hardware: All
>                 OS: Linux
>               Tree: Mainline
>             Status: NEW
>           Severity: high
>           Priority: P1
>          Component: kvm
>           Assignee: virtualization_kvm@kernel-bugs.osdl.org
>           Reporter: nanook@eskimo.com
>         Regression: No
> 
> Created attachment 301614
>   --> https://bugzilla.kernel.org/attachment.cgi?id=301614&action=edit
> The configuration file used to Comile this kernel.
> 
> This behavior has persisted across 5.19.0, 5.19.1, and 5.19.2.  While the
> kernel I am taking this example from is tainted (owing to using Intel
> development drivers for GPU virtualization), it is also occurring on
> non-tainted kernels on servers with no development or third party modules
> installed.
> 
> INFO: task CPU 2/KVM:2343 blocked for more than 1228 seconds.
> [207177.050049]       Tainted: G     U    I       5.19.2 #1
> [207177.050050] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables
> this message.
> [207177.050051] task:CPU 2/KVM       state:D stack:    0 pid: 2343 ppid:    
> 1
> flags:0x00000002
> [207177.050054] Call Trace:
> [207177.050055]  <TASK>
> [207177.050056]  __schedule+0x359/0x1400
> [207177.050060]  ? kvm_mmu_page_fault+0x1ee/0x980
> [207177.050062]  ? kvm_set_msr_common+0x31f/0x1060
> [207177.050065]  schedule+0x5f/0x100
> [207177.050066]  schedule_preempt_disabled+0x15/0x30
> [207177.050068]  __mutex_lock.constprop.0+0x4e2/0x750
> [207177.050070]  ? aa_file_perm+0x124/0x4f0
> [207177.050071]  __mutex_lock_slowpath+0x13/0x20
> [207177.050072]  mutex_lock+0x25/0x30
> [207177.050075]  intel_vgpu_emulate_mmio_read+0x5d/0x3b0 [kvmgt]

This isn't a KVM problem, it's a KVMGT problem (despite the name, KVMGT is very
much not KVM).

> [207177.050084]  intel_vgpu_rw+0xb8/0x1c0 [kvmgt]
> [207177.050091]  intel_vgpu_read+0x20d/0x250 [kvmgt]
> [207177.050097]  vfio_device_fops_read+0x1f/0x40
> [207177.050100]  vfs_read+0x9b/0x160
> [207177.050102]  __x64_sys_pread64+0x93/0xd0
> [207177.050104]  do_syscall_64+0x58/0x80
> [207177.050106]  ? kvm_on_user_return+0x84/0xe0
> [207177.050107]  ? fire_user_return_notifiers+0x37/0x70
> [207177.050109]  ? exit_to_user_mode_prepare+0x41/0x200
> [207177.050111]  ? syscall_exit_to_user_mode+0x1b/0x40
> [207177.050112]  ? do_syscall_64+0x67/0x80
> [207177.050114]  ? irqentry_exit+0x54/0x70
> [207177.050115]  ? sysvec_call_function_single+0x4b/0xa0
> [207177.050116]  entry_SYSCALL_64_after_hwframe+0x63/0xcd
> [207177.050118] RIP: 0033:0x7ff51131293f
> [207177.050119] RSP: 002b:00007ff4ddffa260 EFLAGS: 00000293 ORIG_RAX:
> 0000000000000011
> [207177.050121] RAX: ffffffffffffffda RBX: 00005599a6835420 RCX:
> 00007ff51131293f
> [207177.050122] RDX: 0000000000000004 RSI: 00007ff4ddffa2a8 RDI:
> 0000000000000027
> [207177.050123] RBP: 0000000000000004 R08: 0000000000000000 R09:
> 00000000ffffffff
> [207177.050124] R10: 0000000000065f10 R11: 0000000000000293 R12:
> 0000000000065f10
> [207177.050124] R13: 00005599a6835330 R14: 0000000000000004 R15:
> 0000000000065f10
> [207177.050126]  </TASK>
> 
>      I am seeing this on Intel i7-6700k, i7-6850k, and i7-9700k platforms.
> 
>      This did not happen on 5.17 kernels, and 5.18 kernels never ran stable
> enough on my platforms to actually run them for more than a few minutes.
> 
>      Likewise 6.0-rc1 has not been stable enough to run in production.  After
> less than three hours running on my workstation it locked hard with even the
> magic sys-request key being unresponsive and only power cycling the machine
> got
> it back.
> 
>      The operating system in use for the host on all machines is Ubuntu
>      22.04.
> 
>      Guests vary with Ubuntu 22.04 being the most common but also Mint,
>      Debian,
> Manjaro, Centos, Fedora, ScientificLinux, Zorin, and Windows being in use.
> 
>      I see the same issue manifest on platforms running only Ubuntu guests as
> with guests of varying operating systems.  
> 
>      The configuration file I used to compile this kernel is attached.  I
> compiled it with gcc 12.1.0.
> 
>      This behavior does not manifest itself instantly, typically the machine
> needs to be running 3-7 days before it does.  Once it does guests keep
> stalling
> and restarting libvirtd does not help.  Only thing that seems to is a hard
> reboot of the physical host.  For this reason I believe the issue lies
> strictly
> with the host and not the guests.
> 
>      I have listed it as a severity of high since it is completely service
> interrupting.
> 
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