Re: [Xen-devel] [PATCHv6 1/2] x86/ept: invalidate guest physical mappings on VMENTER

["Tian, Kevin" <kevin.tian@xxxxxxxxx>]

> From: David Vrabel [mailto:david.vrabel@xxxxxxxxxx]
> Sent: Friday, December 18, 2015 9:51 PM
> 
> If a guest allocates a page and the tlbflush_timestamp on the page
> indicates that a TLB flush of the previous owner is required, only the
> linear and combined mappings are invalidated.  The guest-physical
> mappings are not invalidated.
> 
> This is currently safe because the EPT code ensures that the
> guest-physical and combined mappings are invalidated /before/ the page
> is freed.  However, this prevents us from deferring the EPT invalidate
> until after the page is freed (e.g., to defer the invalidate until the
> p2m locks are released).
> 
> The TLB flush that may be done after allocating page already causes
> the original guest to VMEXIT, thus on VMENTER we can do an INVEPT if
> one is pending.
> 
> This means __ept_sync_domain() need not do anything and the thus the
> on_selected_cpu() call does not need to wait for as long.
> 
> ept_sync_domain() now marks all PCPUs as needing to be invalidated,
> including PCPUs that the domain has not run on.  We still only IPI
> those PCPUs that are active so this does not result in any more INVEPT
> calls.
> 
> We do not attempt to track when PCPUs may have cached translations
> because the only safe way to clear this per-CPU state is if
> immediately after an invalidate the PCPU is not active (i.e., the PCPU
> is not in d->domain_dirty_cpumask).  Since we only invalidate on
> VMENTER or by IPIing active PCPUs this can never happen.
> 
> Signed-off-by: David Vrabel <david.vrabel@xxxxxxxxxx>
> Reviewed-by: George Dunlap <george.dunlap@xxxxxxxxxx>

Acked-by: Kevin Tian <kevin.tian@xxxxxxxxx>

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