Re: [Xen-devel] Regression since Linux Kernel 3.12 due to 64bit pvguest NMIs

[Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>]

On Fri, May 09, 2014 at 10:28:29PM +0200, Sebastian Faerber wrote:
> >
> > Isn't it Xen 3.x based? The Linux pvops kernels I thought only
> > were 4.0 and further compatible?
> 
> Yes, it's Xen 3.x based but i can boot pvops kernels up to 3.11.
> 
> > But anyhow, I presume the:
> >
> > ffffffff810041fd
> >
> > maps to the 'ud2' instruction in 'xen_enable_nmi' ?
> 
> Correct.
> 
> > If you take the 'BUG()' out does it continue running?
> 
> You're right - it works
> 
> --- a/arch/x86/xen/setup.c
> +++ b/arch/x86/xen/setup.c
> @@ -559,8 +559,7 @@ void xen_enable_syscall(void)
>  void __cpuinit xen_enable_nmi(void)
>  {
>  #ifdef CONFIG_X86_64
> -       if (register_callback(CALLBACKTYPE_nmi, nmi))
> -               BUG();
> +       register_callback(CALLBACKTYPE_nmi, nmi);
>  #endif
>  }
>  void __init xen_arch_setup(void)
> 
> 
> Thanks Konrad!
> Would it be possible to guard the NMI Feature so older Xen Versions don't get
> confused and run into this BUG()?

Could you patch your kernel with this patch to double check that it is OK?

Is it OK for me to put 'Reported-and-Tested-by: Sebastian Faerber <email>'
on it?

diff --git a/arch/x86/xen/enlighten.c b/arch/x86/xen/enlighten.c
index 201d09a..c19ae00 100644
--- a/arch/x86/xen/enlighten.c
+++ b/arch/x86/xen/enlighten.c
@@ -746,11 +746,14 @@ static int cvt_gate_to_trap(int vector, const gate_desc 
*val,
                 */
                ;
 #endif
-       } else if (addr == (unsigned long)nmi)
+       } else if (addr == (unsigned long)nmi) {
                /*
-                * Use the native version as well.
+                * Use the native version as well, but for RHEL5
+                * hypervisors it is not implemented.
                 */
-               ;
+               if (!xen_running_on_version_or_later(4,0))
+                       return 0;
+       }
        else {
                /* Some other trap using IST? */
                if (WARN_ON(val->ist != 0))
diff --git a/arch/x86/xen/setup.c b/arch/x86/xen/setup.c
index 0982233..aa3fd34 100644
--- a/arch/x86/xen/setup.c
+++ b/arch/x86/xen/setup.c
@@ -576,6 +576,8 @@ void xen_enable_syscall(void)
 }
 void xen_enable_nmi(void)
 {
+       if (!xen_running_on_version_or_later(4,0))
+               return;
 #ifdef CONFIG_X86_64
        if (register_callback(CALLBACKTYPE_nmi, (char *)nmi))
                BUG();


> 
> Regards,
> Sebastian

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