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Re: [Xen-devel] [PATCH v5 10/17] xen/arm: map_regions_rw_cache: Map the region with p2m->default_access





On 06/07/16 12:22, Julien Grall wrote:


On 06/07/16 12:17, Stefano Stabellini wrote:
On Wed, 6 Jul 2016, Julien Grall wrote:
(CC Tamas)

On 06/07/16 11:43, Stefano Stabellini wrote:
On Tue, 28 Jun 2016, Julien Grall wrote:
The parameter 'access' is used by memaccess to restrict temporarily
the
permission. This parameter should not be used for other purpose (such
as restricting permanently the permission).

The type p2m_mmio_direct will map the region Read-Write and
non-executable. Note that this is already the current behavior with
the
combination of the type and the access. So there is no functional
change.

Signed-off-by: Julien Grall <julien.grall@xxxxxxx>

I could be mistaken, but isn't default_access actually p2m_access_rwx?

By default, the access is p2m_access_rwx. However this can be changed by
memaccess and the new default value is stored in
arch->p2m.default_access. I
have CCed Tamas to confirm that.

Note that this is how the other calls are done.

This patch replaces p2m_access_rw with default_access, which is
p2m_access_rwx by default. Is it actually indended?

Yes, I explained why in the commit message.

"The type p2m_mmio_direct will map the region Read-Write and
non-executable. Note that this is already the current behavior with the
combination of the type and the access. So there is no functional
change."

Thinking a bit more, I will reword the commit message with:

"The parameter 'access' used by memaccess to restrict temporarily the permission. This parameter should not be for other purpose (such as restricting permanently the permission).

Instead, we should use the default_access provided by memaccess. When it is not enabled, the access will be p2m_access_rwx (i.e no restriction applied).

The type p2m_mmio_direct will map the region read-write and non-executable before any further restriction by memaccess. note that this is already the current behavior with the combination of the type and the access. So there is no functional change".

Regards,

--
Julien Grall

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