[PATCH v2] xen/arm: fix arm_iommu_map_page after f9f6b22ab

[Stefano Stabellini <stefano.stabellini@xxxxxxx>]

Up until f9f6b22ab "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.

f9f6b22ab introduced a second caller to iommu_map on ARM:
vgic_v3_its_init_virtual. This specific statement in the
f9f6b22ab commit message is 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:49
[...]
(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.

At a minimum, we need to change the is_domain_direct_mapped(d) check in
arm_iommu_map_page into a domain_use_host_layout(d) check. But in
preparation of exposing vITS to domUs, let's take this opportunity to
generalize the arm_iommu_map_page function further to be more generic
and unopinionated. Move the in-code comment specific to the grant table
can live in grant-table.c instead.

Signed-off-by: Stefano Stabellini <stefano.stabellini@xxxxxxx>
---
 xen/common/grant_table.c                    | 10 ++++++++--
 xen/drivers/passthrough/arm/iommu_helpers.c | 13 +------------
 2 files changed, 9 insertions(+), 14 deletions(-)

diff --git a/xen/common/grant_table.c b/xen/common/grant_table.c
index cf131c43a1..2e08dac656 100644
--- a/xen/common/grant_table.c
+++ b/xen/common/grant_table.c
@@ -1274,8 +1274,14 @@ map_grant_ref(
         }
 
         /*
-         * We're not translated, so we know that dfns and mfns are
-         * the same things, so the IOMMU entry is always 1-to-1.
+         * 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.
+         *
+         * We're not translated, so we know that dfns and mfns are the
+         * same things, so the IOMMU entry is always 1-to-1.
          */
         if ( !(op->flags & GNTMAP_readonly) && node.cnt.wr == 1 )
             kind = IOMMUF_readable | IOMMUF_writable;
diff --git a/xen/drivers/passthrough/arm/iommu_helpers.c 
b/xen/drivers/passthrough/arm/iommu_helpers.c
index 5cb1987481..dae5fc0caa 100644
--- a/xen/drivers/passthrough/arm/iommu_helpers.c
+++ b/xen/drivers/passthrough/arm/iommu_helpers.c
@@ -36,17 +36,6 @@ 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(mfn_x(mfn) != dfn_x(dfn));
-
     /* We only support readable and writable flags */
     if ( !(flags & (IOMMUF_readable | IOMMUF_writable)) )
         return -EINVAL;
@@ -57,7 +46,7 @@ int __must_check arm_iommu_map_page(struct domain *d, dfn_t 
dfn, mfn_t mfn,
      * The function guest_physmap_add_entry replaces the current mapping
      * if there is already one...
      */
-    return guest_physmap_add_entry(d, _gfn(dfn_x(dfn)), _mfn(dfn_x(dfn)),
+    return guest_physmap_add_entry(d, _gfn(dfn_x(dfn)), mfn,
                                    IOMMUF_order(flags), t);
 }
 
-- 
2.25.1