Re: [PATCH] x86/XPTI: fix S3 resume (and CPU offlining in general)

[Andrew Cooper <andrew.cooper3@citrix.com>]

On 24/05/18 14:41, Jan Beulich wrote:
> In commit d1d6fc97d6 ("x86/xpti: really hide almost all of Xen image")
> I've failed to remember the fact that multiple CPUs share a stub
> mapping page. Therefore it is wrong to unconditionally zap the mapping
> when bringing down a CPU; it may only be unmapped when no other online
> CPU uses that same page.
>
> Reported-by: Simon Gaiser <simon@invisiblethingslab.com>
> Signed-off-by: Jan Beulich <jbeulich@suse.com>
>
> --- a/xen/arch/x86/smpboot.c
> +++ b/xen/arch/x86/smpboot.c
> @@ -876,7 +876,21 @@ static void cleanup_cpu_root_pgt(unsigne
>  
>      free_xen_pagetable(rpt);
>  
> -    /* Also zap the stub mapping for this CPU. */
> +    /*
> +     * Also zap the stub mapping for this CPU, if no other online one uses
> +     * the same page.
> +     */
> +    if ( stub_linear )
> +    {
> +        unsigned int other;
> +
> +        for_each_online_cpu(other)

Look over the code, it seems that with spaces is the more common style,
but it is admittedly fairly mixed.

Either way (as that's trivial to fix), Acked-by: Andrew Cooper
<andrew.cooper3@citrix.com>

> +            if ( !((per_cpu(stubs.addr, other) ^ stub_linear) >> PAGE_SHIFT) )
> +            {
> +                stub_linear = 0;
> +                break;
> +            }
> +    }
>      if ( stub_linear )
>      {
>          l3_pgentry_t *l3t = l4e_to_l3e(common_pgt);
>
>
>
>


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