[PATCH v1 11/13] xen/arm: implement "xen,offset" feature when host address provided

[Penny Zheng <Penny.Zheng@xxxxxxx>]

When host address is provided in "xen,shared-mem" property([pbase,
gbase, psize]), it is easy to decide where to map to the borrower
domain if "xen,offset" is also provided.
The partially-shared region shall be starting at pbase + offset, and
ending at pbase + size.

Signed-off-by: Penny Zheng <penny.zheng@xxxxxxx>
---
 xen/arch/arm/domain_build.c | 30 +++++++++++++++++++++++-------
 1 file changed, 23 insertions(+), 7 deletions(-)

diff --git a/xen/arch/arm/domain_build.c b/xen/arch/arm/domain_build.c
index 80d37245a8..95600c640c 100644
--- a/xen/arch/arm/domain_build.c
+++ b/xen/arch/arm/domain_build.c
@@ -1112,7 +1112,7 @@ static int __init assign_shared_memory(struct domain *d,
 
 static int __init borrower_physmap_add_memory(struct domain *d,
                                               struct shm_membank *shm_membank,
-                                              paddr_t gbase)
+                                              paddr_t gbase, paddr_t offset)
 {
     int ret;
     unsigned int i;
@@ -1141,8 +1141,8 @@ static int __init borrower_physmap_add_memory(struct 
domain *d,
     }
     else
     {
-        start = shm_membank->mem.bank->start;
-        size = shm_membank->mem.bank->size;
+        start = shm_membank->mem.bank->start + offset;
+        size = shm_membank->mem.bank->size - offset;
         sgfn = _gfn(PFN_UP(gbase));
 
         /* Set up P2M foreign mapping for borrower domain. */
@@ -1157,7 +1157,7 @@ static int __init borrower_physmap_add_memory(struct 
domain *d,
 
 static int __init append_shm_bank_to_domain(struct kernel_info *kinfo,
                                             paddr_t start, paddr_t size,
-                                            const char *shm_id)
+                                            const char *shm_id, paddr_t offset)
 {
     struct membank *membank;
 
@@ -1170,7 +1170,7 @@ static int __init append_shm_bank_to_domain(struct 
kernel_info *kinfo,
 
     kinfo->shm_mem.bank[kinfo->shm_mem.nr_banks].mem.bank = membank;
     kinfo->shm_mem.bank[kinfo->shm_mem.nr_banks].mem.bank->start = start;
-    kinfo->shm_mem.bank[kinfo->shm_mem.nr_banks].mem.bank->size = size;
+    kinfo->shm_mem.bank[kinfo->shm_mem.nr_banks].mem.bank->size = size - 
offset;
     safe_strcpy(kinfo->shm_mem.bank[kinfo->shm_mem.nr_banks].shm_id, shm_id);
     kinfo->shm_mem.nr_banks++;
 
@@ -1265,6 +1265,7 @@ static int __init process_shm(struct domain *d, struct 
kernel_info *kinfo,
         const char *shm_id;
         bool owner_dom_io = true, paddr_assigned = true;
         struct shm_membank *shm_membank;
+        uint64_t offset = 0UL;
 
         if ( !dt_device_is_compatible(shm_node, "xen,domain-shared-memory-v1") 
)
             continue;
@@ -1288,6 +1289,19 @@ static int __init process_shm(struct domain *d, struct 
kernel_info *kinfo,
         }
         BUG_ON((strlen(shm_id) <= 0) || (strlen(shm_id) >= MAX_SHM_ID_LENGTH));
 
+        /*
+         * If "xen,offset" is provided, then only partial shared memory
+         * shall be mapped to borrower domain.
+         * "xen,offset" is a 64-bit integer and an optional property
+         */
+        dt_property_read_u64(shm_node, "xen,offset", &offset);
+        if ( !IS_ALIGNED(offset, PAGE_SIZE) )
+        {
+            printk("%pd: \"xen,offset\" 0x%lx is not suitably aligned\n",
+                   d, offset);
+            return -EINVAL;
+        }
+
         shm_membank = acquire_shm_membank(shm_id);
         if ( !shm_membank )
         {
@@ -1331,7 +1345,8 @@ static int __init process_shm(struct domain *d, struct 
kernel_info *kinfo,
 
         if ( owner_dom_io || (strcmp(role_str, "borrower") == 0) )
         {
-            ret = borrower_physmap_add_memory(d, shm_membank, gbase);
+            ret = borrower_physmap_add_memory(d, shm_membank, gbase,
+                                              (paddr_t)offset);
             if ( ret )
             {
                 printk(XENLOG_ERR
@@ -1345,7 +1360,8 @@ static int __init process_shm(struct domain *d, struct 
kernel_info *kinfo,
          * Record static shared memory region info for later setting
          * up shm-node in guest device tree.
          */
-        ret = append_shm_bank_to_domain(kinfo, gbase, psize, shm_id);
+        ret = append_shm_bank_to_domain(kinfo, gbase, psize, shm_id,
+                                        (paddr_t)offset);
         if ( ret )
             return ret;
     }
-- 
2.25.1