[PATCH v3 2/3] xen: introduce arch_grant_(un)map_page_identity

[Stefano Stabellini <stefano.stabellini@eu.citrix.com>]

Introduce two arch specific functions to create a new p2m mapping of
granted pages at pfn == mfn.
The x86 implementation just returns ENOSYS.

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>

---
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/arch/arm/p2m.c                 |   22 ++++++++++++++++++++++
 xen/drivers/passthrough/arm/smmu.c |   13 ++-----------
 xen/include/asm-arm/p2m.h          |    4 ++++
 xen/include/asm-x86/p2m.h          |   13 +++++++++++++
 4 files changed, 41 insertions(+), 11 deletions(-)

diff --git a/xen/arch/arm/p2m.c b/xen/arch/arm/p2m.c
index 9960e17..6024b03 100644
--- a/xen/arch/arm/p2m.c
+++ b/xen/arch/arm/p2m.c
@@ -555,6 +555,28 @@ void guest_physmap_remove_page(struct domain *d,
                       pfn_to_paddr(mfn), MATTR_MEM, p2m_invalid);
 }
 
+int arch_grant_map_page_identity(struct domain *d, unsigned long frame,
+                                 bool_t writeable)
+{
+    p2m_type_t t;
+
+    /* This is not an IOMMU mapping but it is not a regular RAM p2m type
+     * either. We are using IOMMU p2m types here to prevent the pages
+     * from being used as grants. */
+    if ( writeable )
+        t = p2m_iommu_map_rw;
+    else
+        t = p2m_iommu_map_ro;
+
+    return guest_physmap_add_entry(d, frame, frame, 0, t);
+}
+
+int arch_grant_unmap_page_identity(struct domain *d, unsigned long frame)
+{
+    guest_physmap_remove_page(d, frame, frame, 0);
+    return 0;
+}
+
 int p2m_alloc_table(struct domain *d)
 {
     struct p2m_domain *p2m = &d->arch.p2m;
diff --git a/xen/drivers/passthrough/arm/smmu.c b/xen/drivers/passthrough/arm/smmu.c
index f4eb2a2..fb0c694 100644
--- a/xen/drivers/passthrough/arm/smmu.c
+++ b/xen/drivers/passthrough/arm/smmu.c
@@ -1539,8 +1539,6 @@ static void arm_smmu_iommu_domain_teardown(struct domain *d)
 static int arm_smmu_map_page(struct domain *d, unsigned long gfn,
                              unsigned long mfn, unsigned int flags)
 {
-    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
@@ -1555,12 +1553,7 @@ static int arm_smmu_map_page(struct domain *d, unsigned long gfn,
     if ( !(flags & (IOMMUF_readable | IOMMUF_writable)) )
         return -EINVAL;
 
-    t = (flags & IOMMUF_writable) ? p2m_iommu_map_rw : p2m_iommu_map_ro;
-
-    /* The function guest_physmap_add_entry replaces the current mapping
-     * if there is already one...
-     */
-    return guest_physmap_add_entry(d, gfn, mfn, 0, t);
+    return arch_grant_map_page_identity(d, mfn, flags & IOMMUF_writable);
 }
 
 static int arm_smmu_unmap_page(struct domain *d, unsigned long gfn)
@@ -1571,9 +1564,7 @@ static int arm_smmu_unmap_page(struct domain *d, unsigned long gfn)
     if ( !is_domain_direct_mapped(d) )
         return -EINVAL;
 
-    guest_physmap_remove_page(d, gfn, gfn, 0);
-
-    return 0;
+    return arch_grant_unmap_page_identity(d, gfn);
 }
 
 static const struct iommu_ops arm_smmu_iommu_ops = {
diff --git a/xen/include/asm-arm/p2m.h b/xen/include/asm-arm/p2m.h
index 911d32d..b682f51 100644
--- a/xen/include/asm-arm/p2m.h
+++ b/xen/include/asm-arm/p2m.h
@@ -181,6 +181,10 @@ static inline int get_page_and_type(struct page_info *page,
     return rc;
 }
 
+int arch_grant_map_page_identity(struct domain *d, unsigned long frame,
+                                 bool_t writeable);
+int arch_grant_unmap_page_identity(struct domain *d, unsigned long frame);
+
 #endif /* _XEN_P2M_H */
 
 /*
diff --git a/xen/include/asm-x86/p2m.h b/xen/include/asm-x86/p2m.h
index 0ddbadb..faead11 100644
--- a/xen/include/asm-x86/p2m.h
+++ b/xen/include/asm-x86/p2m.h
@@ -717,6 +717,19 @@ static inline unsigned int p2m_get_iommu_flags(p2m_type_t p2mt)
 
     return flags;
 }
+ 
+static inline int arch_grant_map_page_identity(struct domain *d,
+                                               unsigned long frame,
+                                               bool_t writeable)
+{
+    return -ENOSYS;
+}
+
+static inline int arch_grant_unmap_page_identity(struct domain *d,
+                                                 unsigned long frame)
+{
+    return -ENOSYS;
+}
 
 #endif /* _XEN_P2M_H */
 
-- 
1.7.10.4