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

[Peter Lieven]

On 05.07.2012 10:51, Xiao Guangrong wrote:
> 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?
Thank you very much, this fixes the issue I have seen.

Thanks,
Peter