Re: [Xen-devel] [PATCH] x86/p2m: Stop other vcpus using a nested p2m before clearing it

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 07.02.17 at 19:48, <andrew.cooper3@xxxxxxxxxx> wrote:
> Until the IPI has completed, other processors might be running on this nested
> p2m object.  clear_domain_page() does not guarantee to make 8-byte atomic
> updates, which means that a pagewalk on a remote processor might encounter a
> partial update.
> 
> This is currently safe as other issues prevents a nested p2m ever being shared
> between two cpus (although this is contrary to the original plan).
> 
> Setting p2m->np2m_base to P2M_BASE_EADDR before the IPI ensures that the IPI'd
> processors won't continue to use the flushed mappings.
> 
> While modifying this function, remove all the trailing whitespace and tweak
> style in the affected areas.
> 
> Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>

Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
but ...

> @@ -1633,19 +1635,21 @@ p2m_flush_table(struct p2m_domain *p2m)
>  
>      /* This is no longer a valid nested p2m for any address space */
>      p2m->np2m_base = P2M_BASE_EADDR;
> -    
> -    /* Zap the top level of the trie */
> -    mfn = pagetable_get_mfn(p2m_get_pagetable(p2m));
> -    clear_domain_page(mfn);
>  
>      /* Make sure nobody else is using this p2m table */
>      nestedhvm_vmcx_flushtlb(p2m);
>  
> +    /* Zap the top level of the trie */

s/trie/tree/ here, as you touch it anyway?

Jan


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