Re: [Xen-devel] [PATCH] xen/x86: clear per cpu stub page information in cpu_smpboot_free()

[Wei Liu <wl@xxxxxxx>]

On Wed, Jan 08, 2020 at 12:01:48PM +0100, Juergen Gross wrote:
> cpu_smpboot_free() removes the stubs for the cpu going offline, but it
> isn't clearing the related percpu variables. This will result in
> crashes when a stub page is released due to all related cpus gone
> offline and one of those cpus going online later.
> 
> Fix that by clearing stubs.addr and stubs.mfn in order to allocate a
> new stub page when needed.
> 
> Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
> ---
>  xen/arch/x86/smpboot.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/xen/arch/x86/smpboot.c b/xen/arch/x86/smpboot.c
> index 7e29704080..46c0729214 100644
> --- a/xen/arch/x86/smpboot.c
> +++ b/xen/arch/x86/smpboot.c
> @@ -945,6 +945,8 @@ static void cpu_smpboot_free(unsigned int cpu, bool 
> remove)
>                               (per_cpu(stubs.addr, cpu) | ~PAGE_MASK) + 1);
>          if ( i == STUBS_PER_PAGE )
>              free_domheap_page(mfn_to_page(mfn));
> +        per_cpu(stubs.addr, cpu) = 0;
> +        per_cpu(stubs.mfn, cpu) = 0;

Shouldn't the mfn be set to INVALID_MFN instead?

Wei.

>      }
>  
>      FREE_XENHEAP_PAGE(per_cpu(compat_gdt, cpu));
> -- 
> 2.16.4
> 

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