Re: [Bugme-new] [Bug 10246] New: "in" after successful ioperm() results in SEGV after kvm use

Re: [Bugme-new] [Bug 10246] New: "in" after successful ioperm() results in SEGV after kvm use

[Andrew Morton]

On Fri, 14 Mar 2008 18:48:15 -0700 (PDT) bugme-daemon@bugzilla.kernel.org wrote:

> http://bugzilla.kernel.org/show_bug.cgi?id=10246
> 
>            Summary: "in" after successful ioperm() results in SEGV after kvm
>                     use
>            Product: Memory Management
>            Version: 2.5
>      KernelVersion: 2.6.25-rc5
>           Platform: All
>         OS/Version: Linux
>               Tree: Mainline
>             Status: NEW
>           Severity: normal
>           Priority: P1
>          Component: Other
>         AssignedTo: akpm@osdl.org
>         ReportedBy: kees@outflux.net
> 
> 
> Latest working kernel version: N/A
> Earliest failing kernel version: 2.6.24
> Distribution: Ubuntu, but tested with mainline
> Hardware Environment: intel mobo, Intel(R) Core(TM)2 Quad CPU Q6600@2.40GHz
> Software Environment: kvm 62 (x86_64)
> Problem Description:
> 
> After a successful ioperm() call, otherwise valid "in" instructions will segv
> if a kvm VM has started.
> 
> Steps to reproduce:
> 
> 1) run attached reproducer prior to starting a kvm VM, results are:
> # ./ioperm
> getting 0x3b4-0x3df permission...
> fetching 0x3cc...
> ok: 1
> 
> 2) start a kvm VM (bug exists only after actually starting a guest VM)
> 
> 3) run reproducer, which now fails:
> # ./ioperm
> getting 0x3b4-0x3df permission...
> fetching 0x3cc...
> Segmentation fault (core dumped)
> 
> Note that it does not always fail.  Running within gdb seems to reduce the
> chances that it will fail.  But when it does, it is clearly the "in" that is
> failing:
> 
> Program received signal SIGSEGV, Segmentation fault.
> 0x00000000004006e4 in inb ()
> (gdb) x/1i $pc
> 0x4006e4 <inb+12>:      in     (%dx),%al
> (gdb) info reg rdx
> rdx            0x3cc    972
> 
> I have had the sense that running the CPUs at full load (niced) increases the
> chance for failure.
> 

There is a testcase in the bugzilla report.

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