Re: [Xen-devel] [RFC 21/22] xen/arm: p2m: Re-implement p2m_set_mem_access using p2m_{set, get}_entry

[Julien Grall <julien.grall@xxxxxxx>]

On 28/07/16 16:04, Razvan Cojocaru wrote:
> On 07/28/2016 05:51 PM, Julien Grall wrote:
> > The function p2m_set_mem_access can be re-implemented using the generic
> > functions p2m_get_entry and __p2m_set_entry.
> >
> > Note that because of the implementation of p2m_get_entry, a TLB
> > invalidation instruction will be issued for each 4KB page. Therefore the
> > performance of memaccess will be impacted, however the function is now
> > safe on all the processors.
> >
> > Also the function apply_p2m_changes is dropped completely as it is not
> > unused anymore.
> >
> > Signed-off-by: Julien Grall <julien.grall@xxxxxxx>
> > Cc: Razvan Cojocaru <rcojocaru@xxxxxxxxxxxxxxx>
> > Cc: Tamas K Lengyel <tamas@xxxxxxxxxxxxx>
> >
> > ---
> >     I have not ran any performance test with memaccess for now, but I
> >     expect an important and unavoidable impact because of how memaccess
> >     has been designed to workaround hardware limitation. Note that might
> >     be possible to re-work memaccess work on superpage but this should
> >     be done in a separate patch.
> > ---
> >  xen/arch/arm/p2m.c | 329 +++++++----------------------------------------------
> >  1 file changed, 38 insertions(+), 291 deletions(-)
> Thanks for the CC!
Hi Razvan,

> This seems to only impact ARM, are there any planned changes for x86
> along these lines as well?
The break-before-make sequence is required by the ARM architecture. I 
don't know the x86 architecture, you can ask the x86 maintainers if this 
is something necessary.
Regards,

--
Julien Grall

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