xen/arm: fix arm_iommu_map_page after f9f6b22abf

Up until f9f6b22abf "xen/arm: Map ITS doorbell register to IOMMU page
tables" the only caller of iommu_map on ARM was grant_table.c which has
a specific usage model and restrictions as described by the in-code
comment in arm_iommu_map_page.

f9f6b22abf introduced a second caller to iommu_map on ARM:
vgic_v3_its_init_virtual. This specific statement in the
f9f6b22abf commit message is partially wrong:

"Note that the 1:1 check in arm_iommu_map_page remains for now, as
virtual ITSes are currently only created for hwdom where the doorbell
mapping is always 1:1."

Leading to crashes any time the hardware domain is not direct-mapped
(e.g. cache coloring and non-Dom0 hardware domain):

(XEN) Xen BUG at drivers/passthrough/arm/iommu_helpers.c:47
[...]
(XEN) Xen call trace:
(XEN)    [<00000a000024c758>] arm_iommu_map_page+0x80/0x90 (PC)
(XEN)    [<00000a000024c750>] arm_iommu_map_page+0x78/0x90 (LR)
(XEN)    [<00000a0000250884>] iommu_map+0xcc/0x29c
(XEN)    [<00000a0000288024>] vgic_v3_its_init_domain+0x18c/0x1e8
(XEN)    [<00000a0000285228>] vgic-v3.c#vgic_v3_domain_init+0x168/0x21c
(XEN)    [<00000a0000281dcc>] domain_vgic_init+0x14c/0x210
(XEN)    [<00000a00002705a4>] arch_domain_create+0x150/0x1f0
(XEN)    [<00000a00002055e8>] domain_create+0x47c/0x6c0
(XEN)    [<00000a00002cf090>] create_domUs+0x7f8/0x8cc
(XEN)    [<00000a00002eb588>] start_xen+0x8f4/0x998
(XEN)    [<00000a000020018c>] head.o#primary_switched+0x4/0x10

Specifically, non-1:1 hardware domain exists with cache coloring
enabled. For that, is_domain_direct_mapped(d) is false but
domain_use_host_layout(d) is true.

Change the is_domain_direct_mapped(d) checks in arm_iommu_map_page and
arm_iommu_unmap_page into domain_use_host_layout(d) checks.

Drop stale in-code comment specific to grant table mappings.

Fixes: f9f6b22abf ("xen/arm: Map ITS doorbell register to IOMMU page tables")
Signed-off-by: Stefano Stabellini <stefano.stabellini@amd.com>
Signed-off-by: Stewart Hildebrand <stewart.hildebrand@amd.com>
Tested-by: Jason Andryuk <jason.andryuk@amd.com>
Reviewed-by: Julien Grall <jgrall@amazon.com>

xen/drivers/passthrough/arm/iommu_helpers.c

@@ -36,15 +36,7 @@ int __must_check arm_iommu_map_page(struct domain *d, dfn_t dfn, mfn_t mfn,
 {
     p2m_type_t t;
 
-    /*
-     * Grant mappings can be used for DMA requests. The dev_bus_addr
-     * returned by the hypercall is the MFN (not the IPA). For device
-     * protected by an IOMMU, Xen needs to add a 1:1 mapping in the domain
-     * p2m to allow DMA request to work.
-     * This is only valid when the domain is directed mapped. Hence this
-     * function should only be used by gnttab code with gfn == mfn == dfn.
-     */
-    BUG_ON(!is_domain_direct_mapped(d));
+    BUG_ON(!domain_use_host_layout(d));
     BUG_ON(mfn_x(mfn) != dfn_x(dfn));
 
     /* We only support readable and writable flags */
@@ -66,11 +58,7 @@ int __must_check arm_iommu_unmap_page(struct domain *d, dfn_t dfn,
                                       unsigned int order,
                                       unsigned int *flush_flags)
 {
-    /*
-     * This function should only be used by gnttab code when the domain
-     * is direct mapped (i.e. gfn == mfn == dfn).
-     */
-    if ( !is_domain_direct_mapped(d) )
+    if ( !domain_use_host_layout(d) )
         return -EINVAL;
 
     return guest_physmap_remove_page(d, _gfn(dfn_x(dfn)), _mfn(dfn_x(dfn)),