Re: [linux-linus test] 183794: regressions - FAIL

[Juergen Gross <jgross@xxxxxxxx>]

On 23.11.23 00:07, Stefano Stabellini wrote:
> On Wed, 22 Nov 2023, Juergen Gross wrote:
> > On 22.11.23 04:07, Stefano Stabellini wrote:
> > > On Mon, 20 Nov 2023, Stefano Stabellini wrote:
> > > > On Mon, 20 Nov 2023, Juergen Gross wrote:
> > > > > On 20.11.23 03:21, osstest service owner wrote:
> > > > > > flight 183794 linux-linus real [real]
> > > > > > http://logs.test-lab.xenproject.org/osstest/logs/183794/
> > > > > >
> > > > > > Regressions :-(
> > > > > >
> > > > > > Tests which did not succeed and are blocking,
> > > > > > including tests which could not be run:
> > > > > >     test-arm64-arm64-examine      8 reboot                   fail REGR.
> > > > > > vs.
> > > > > > 183766
> > > > > I'm seeing the following in the serial log:
> > > > >
> > > > > Nov 20 00:25:41.586712 [    0.567318] kernel BUG at
> > > > > arch/arm64/xen/../../arm/xen/enlighten.c:164!
> > > > > Nov 20 00:25:41.598711 [    0.574002] Internal error: Oops - BUG:
> > > > > 00000000f2000800 [#1] PREEMPT SMP
> > > > >
> > > > > The related source code lines in the kernel are:
> > > > >
> > > > > ········err = HYPERVISOR_vcpu_op(VCPUOP_register_vcpu_info,
> > > > > xen_vcpu_nr(cpu),
> > > > > ································ &info);
> > > > > ········BUG_ON(err);
> > > > >
> > > > > I suspect commit 20f3b8eafe0ba to be the culprit.
> > > > >
> > > > > Stefano, could you please have a look?
> > > The good news and bad news is that I cannot repro this neither with nor
> > > without CONFIG_UNMAP_KERNEL_AT_EL0. I looked at commit 20f3b8eafe0ba but
> > > I cannot see anything wrong with it. Looking at the register dump, from:
> > >
> > > x0 : fffffffffffffffa
> > >
> > > I am guessing the error was -ENXIO which is returned from map_guest_area
> > > in Xen.
> > >
> > > Could it be that the struct is crossing a page boundary? Or that it is
> > > not 64-bit aligned? Do we need to do something like the following?
> > >
> > > diff --git a/arch/arm/xen/enlighten.c b/arch/arm/xen/enlighten.c
> > > index 9afdc4c4a5dc..5326070c5dc0 100644
> > > --- a/arch/arm/xen/enlighten.c
> > > +++ b/arch/arm/xen/enlighten.c
> > > @@ -484,7 +485,7 @@ static int __init xen_guest_init(void)
> > >          * for secondary CPUs as they are brought up.
> > >          * For uniformity we use VCPUOP_register_vcpu_info even on cpu0.
> > >          */
> > > -       xen_vcpu_info = alloc_percpu(struct vcpu_info);
> > > +       xen_vcpu_info = __alloc_percpu(struct vcpu_info, PAGE_SIZE);
> > >         if (xen_vcpu_info == NULL)
> > >                 return -ENOMEM;
> > >    
> > May I suggest to use a smaller alignment? What about:
> >
> > 1 << fls(sizeof(struct vcpu_info) - 1)
> See below
>
> ---
> [PATCH] arm/xen: fix xen_vcpu_info allocation alignment
>
> xen_vcpu_info is a percpu area than needs to be mapped by Xen.
> Currently, it could cross a page boundary resulting in Xen being unable
> to map it:
>
> [    0.567318] kernel BUG at arch/arm64/xen/../../arm/xen/enlighten.c:164!
> [    0.574002] Internal error: Oops - BUG: 00000000f2000800 [#1] PREEMPT SMP
>
> Fix the issue by using __alloc_percpu and requesting alignment for the
> memory allocation.
>
> Signed-off-by: Stefano Stabellini <stefano.stabellini@xxxxxxx>
>
> diff --git a/arch/arm/xen/enlighten.c b/arch/arm/xen/enlighten.c
> index 9afdc4c4a5dc..09eb74a07dfc 100644
> --- a/arch/arm/xen/enlighten.c
> +++ b/arch/arm/xen/enlighten.c
> @@ -484,7 +484,8 @@ static int __init xen_guest_init(void)
>          * for secondary CPUs as they are brought up.
>          * For uniformity we use VCPUOP_register_vcpu_info even on cpu0.
>          */
> -       xen_vcpu_info = alloc_percpu(struct vcpu_info);
> +       xen_vcpu_info = __alloc_percpu(sizeof(struct vcpu_info),
> +                                              1 << fls(sizeof(struct 
> vcpu_info) - 1));
Nit: one tab less, please (can be fixed while committing).

>         if (xen_vcpu_info == NULL)
>                 return -ENOMEM;
>   
Reviewed-by: Juergen Gross <jgross@xxxxxxxx>


Juergen

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