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 <si...@invisiblethingslab.com>
> Signed-off-by: Jan Beulich <jbeul...@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.coop...@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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