xen/arm: grant: Add another entry to map MFN 1:1 in dom0 p2m

From: Julien Grall <julien.grall@linaro.org>

Grant mappings can be used for DMA requests. Currently the dev_bus_addr returned
by the hypercall is the MFN (not the IPA). Guest expects to be able the returned
address for DMA. When the device is protected by IOMMU the request will fail.
Therefore, we have to add 1:1 mapping in the domain p2m to allow DMA request
to work.

This is valid because DOM0 has its memory mapped 1:1 and therefore we know
that RAM and devices cannot clash.

If the guest only owns protected device, the return dev_bus_addr should be an
IPA. This will allow us to remove safely the 1:1 mapping and make grant mapping
works correctly in the guest. For now, this is not addressed by this patch.

The grant mapping code does the reference counting on every MFN and will
call iommu_{map,unmap}_page when necessary. This was already handle for x86
PV guests, so we can reuse the same code path for ARM guest.

Note: this is the backport of commit
552710b388630dfa461932940a998e120c42277d.  In the backport
gnttab_need_iommu_mapping has been disabled for ARM, because there is no
SMMU support yet. It will be re-enabled by a later commit.
Also iommu_map_page and iommu_unmap_page have been stubbed out on ARM.


Signed-off-by: Julien Grall <julien.grall@linaro.org>
Signed-off-by: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
Acked-by: Ian Campbell <ian.campbell@citrix.com>
Acked-by: Jan Beulich <jbeulich@suse.com>
[ ijc s/ld/d/ in both arch's gnttab_need_iommu_mapping() ]
xen/x86: introduce is_domain_direct_mapped(d) as ((void)(d), 0) on x86

Signed-off-by: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
Acked-by: Jan Beulich <jbeulich@suse.com>

---

Changes in v4:
- remove define is_domain_direct_mapped in common/memory.c;
- define is_domain_direct_mapped as ((void)(d), 0)
xen: introduce arch_grant_(un)map_page_identity

Introduce two arch specific functions to create a new p2m mapping of
granted pages at pfn == mfn.
We don't an x86 implementation as these functions should never be
compiled on x86 (they are called from an if (0) statement).

Base the implementation of arm_smmu_(un)map_page on
arch_grant_(un)map_page_identity.

Signed-off-by: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
Acked-by: Julien Grall <julien.grall@linaro.org>
Acked-by: Jan Beulich <jbeulich@suse.com>

---

Changes in v5:
- actually define arch_grant_(un)map_page_identity as extern without
implementation on x86.

Changes in v4:
- declare the x86 implementations as extern;
- add ASSERTs to ARM implementations.

Changes in v3:
- fix commit title;
- use p2m_iommu types;
- call arch_grant_(un)map_page_identity functions from
arm_smmu_(un)map_page.
xen/arm: introduce XENFEAT_grant_map_identity

The flag specifies that the hypervisor maps a grant page to guest
physical address == machine address of the page in addition to the
normal grant mapping address.

Frontends are allowed to map the same page multiple times using multiple
grant references. On the backend side it can be difficult to find out
the physical address corresponding to a particular machine address,
especially at the completion of a dma operation. To simplify address
translations, we introduce a second mapping of the grant at physical
address == machine address so that dom0 can issue cache maintenance
operations without having to find the pfn.

Call arch_grant_map_page_identity and arch_grant_unmap_page_identity
from __gnttab_map_grant_ref and __gnttab_unmap_common to introduce the
second mapping if the domain is directly mapped. To do so we also need
to change gnttab_need_iommu_mapping to just be defined as
is_domain_direct_mapped on arm.

Remove arm_smmu_map_page and arm_smmu_unmap_page as they have become
unused.

Signed-off-by: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
Acked-by: Jan Beulich <jbeulich@suse.com>
Acked-by: Julien Grall <julien.grall@linaro.org>

---

Changes in v5:
- fix coding style;
- remove arm_smmu_map_page and arm_smmu_unmap_page.

Changes in v4:
- add XENFEAT_grant_map_identity if is_domain_direct_mapped;
- remove gnttab_need_identity_mapping, check is_domain_direct_mapped
instead;
- define gnttab_need_iommu_mapping as is_domain_direct_mapped on arm.

Changes in v3:
- introduce gnttab_need_identity_mapping;
- check gnttab_need_identity_mapping in __gnttab_map_grant_ref and
__gnttab_unmap_common.

Changes in v2:
- rename XENFEAT_grant_map_11 to XENFEAT_grant_map_identity;
- remove superfluous ifdef CONFIG_ARM in xen/common/kernel.c;
- don't modify gnttab_need_iommu_mapping;
- call arch_grant_map_page_identity and arch_grant_unmap_page_identity
from grant_table functions.
Merge branch grant_map_identity_4.4_2 into stable-4.4

Conflicts:
	xen/arch/arm/p2m.c