Re: [Qemu-devel] race between kvm-kmod-3.0 and kvm-kmod-3.3 // was: race condition in qemu-kvm-1.0.1

[Xiao Guangrong]

On 06/28/2012 05:11 PM, Peter Lieven wrote:

> that here is bascially whats going on:
> 
>   qemu-kvm-1.0-2506  [010] 60996.908000: kvm_mmio:             mmio read len 
> 3 gpa 0xa0000 val 0x10ff
>     qemu-kvm-1.0-2506  [010] 60996.908000: vcpu_match_mmio:      gva 0xa0000 
> gpa 0xa0000 Read GPA
>     qemu-kvm-1.0-2506  [010] 60996.908000: kvm_mmio:             mmio 
> unsatisfied-read len 1 gpa 0xa0000 val 0x0
>     qemu-kvm-1.0-2506  [010] 60996.908000: kvm_userspace_exit:   reason 
> KVM_EXIT_MMIO (6)
>     qemu-kvm-1.0-2506  [010] 60996.908000: kvm_mmio:             mmio read 
> len 3 gpa 0xa0000 val 0x10ff
>     qemu-kvm-1.0-2506  [010] 60996.908000: vcpu_match_mmio:      gva 0xa0000 
> gpa 0xa0000 Read GPA
>     qemu-kvm-1.0-2506  [010] 60996.908000: kvm_mmio:             mmio 
> unsatisfied-read len 1 gpa 0xa0000 val 0x0
>     qemu-kvm-1.0-2506  [010] 60996.908000: kvm_userspace_exit:   reason 
> KVM_EXIT_MMIO (6)
>     qemu-kvm-1.0-2506  [010] 60996.908000: kvm_mmio:             mmio read 
> len 3 gpa 0xa0000 val 0x10ff
>     qemu-kvm-1.0-2506  [010] 60996.908000: vcpu_match_mmio:      gva 0xa0000 
> gpa 0xa0000 Read GPA
>     qemu-kvm-1.0-2506  [010] 60996.908000: kvm_mmio:             mmio 
> unsatisfied-read len 1 gpa 0xa0000 val 0x0
>     qemu-kvm-1.0-2506  [010] 60996.908000: kvm_userspace_exit:   reason 
> KVM_EXIT_MMIO (6)
>     qemu-kvm-1.0-2506  [010] 60996.908000: kvm_mmio:             mmio read 
> len 3 gpa 0xa0000 val 0x10ff
>     qemu-kvm-1.0-2506  [010] 60996.908000: vcpu_match_mmio:      gva 0xa0000 
> gpa 0xa0000 Read GPA
>     qemu-kvm-1.0-2506  [010] 60996.908000: kvm_mmio:             mmio 
> unsatisfied-read len 1 gpa 0xa0000 val 0x0
>     qemu-kvm-1.0-2506  [010] 60996.908000: kvm_userspace_exit:   reason 
> KVM_EXIT_MMIO (6)
> 

There are two mmio emulation after user-space-exit, it is caused by mmio
read access which spans two pages. But it should be fixed by:

commit f78146b0f9230765c6315b2e14f56112513389ad
Author: Avi Kivity <address@hidden>
Date:   Wed Apr 18 19:22:47 2012 +0300

    KVM: Fix page-crossing MMIO

    MMIO that are split across a page boundary are currently broken - the
    code does not expect to be aborted by the exit to userspace for the
    first MMIO fragment.

    This patch fixes the problem by generalizing the current code for handling
    16-byte MMIOs to handle a number of "fragments", and changes the MMIO
    code to create those fragments.

    Signed-off-by: Avi Kivity <address@hidden>
    Signed-off-by: Marcelo Tosatti <address@hidden>

Could you please pull the code from:
https://git.kernel.org/pub/scm/virt/kvm/kvm.git
and trace it again?