Re: [Xen-devel] [PATCH] xen/arm: create_p2m_entries has to flush TLBs on every CPU

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Fri, 2014-04-18 at 17:12 +0100, Julien Grall wrote:
> The function create_p2m_entries creates mappings in second-level page tables
> which is shared between every CPU.

You say create_p2m_entries twice but then patch create_xen_entries. Is
it the patch or the description which is wrong?

> Only flushing TLBs on local processor may result to wrong behaviour
> when io{re,un}map is used.

From this sounds like it's the desription?

> Signed-off-by: Julien Grall <julien.grall@xxxxxxxxxx>
> ---
> 
> This patch is candidate to be backported to Xen 4.4.
> 
> create_p2m_entries is only used by vmap ( iore{,un}map functions.
> 
> Upstream Xen 4.4 calls these functions only when 1 CPU is online so it's
> "safe". People might want to use them when multiple CPUs are online.
> 
> Ian: Do you plan to backport your tlb series? If not, this patch will have
> to slighty change because Xen 4.4 doesn't have TLBs helper to flush xen
> data on every cpus.

I wasn't planning to backport the tlb series, but I could look at
backporting the required bits I suppose.

However, is it needed? Does 4.4 make any ioremap calls where this would
actually hurt? I think all the uses in xen/arch/arm/platforms/*.c are
short lived and only accessed from the current cpu. The one in
xen/drivers/video/arm_hdlcd.c is done before we go SMP anyway.

Ian.



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