[PATCH 1/3] xen/arm/dom0less-build: Alloc magic pages for Dom0less DomUs from hypervisor

[Henry Wang <xin.wang2@xxxxxxx>]

There are use cases (for example using the PV driver) in Dom0less
setup that require Dom0less DomUs start immediately with Dom0, but
initialize XenStore later after Dom0's successful boot and call to
the init-dom0less application.

An error message can seen from the init-dom0less application on
1:1 direct-mapped domains:
```
Allocating magic pages
memory.c:238:d0v0 mfn 0x39000 doesn't belong to d1
Error on alloc magic pages
```
This is because currently the magic pages for Dom0less DomUs are
populated by the init-dom0less app through populate_physmap(), and
populate_physmap() automatically assumes gfn == mfn for 1:1 direct
mapped domains. This cannot be true for the magic pages that are
allocated later from the init-dom0less application executed in Dom0.
For domain using statically allocated memory but not 1:1 direct-mapped,
similar error "failed to retrieve a reserved page" can be seen as the
reserved memory list is empty at that time.

To solve above issue, this commit allocates the magic pages for
Dom0less DomUs at the domain construction time. The base address/PFN
of the magic page region will be noted and communicated to the
init-dom0less application in Dom0.

Reported-by: Alec Kwapis <alec.kwapis@xxxxxxxxxxxxx>
Suggested-by: Daniel P. Smith <dpsmith@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Henry Wang <xin.wang2@xxxxxxx>
---
 tools/libs/guest/xg_dom_arm.c |  1 -
 xen/arch/arm/dom0less-build.c | 22 ++++++++++++++++++++++
 xen/include/public/arch-arm.h |  1 +
 3 files changed, 23 insertions(+), 1 deletion(-)

diff --git a/tools/libs/guest/xg_dom_arm.c b/tools/libs/guest/xg_dom_arm.c
index 2fd8ee7ad4..8cc7f27dbb 100644
--- a/tools/libs/guest/xg_dom_arm.c
+++ b/tools/libs/guest/xg_dom_arm.c
@@ -25,7 +25,6 @@
 
 #include "xg_private.h"
 
-#define NR_MAGIC_PAGES 4
 #define CONSOLE_PFN_OFFSET 0
 #define XENSTORE_PFN_OFFSET 1
 #define MEMACCESS_PFN_OFFSET 2
diff --git a/xen/arch/arm/dom0less-build.c b/xen/arch/arm/dom0less-build.c
index fb63ec6fd1..40dc85c759 100644
--- a/xen/arch/arm/dom0less-build.c
+++ b/xen/arch/arm/dom0less-build.c
@@ -834,11 +834,33 @@ static int __init construct_domU(struct domain *d,
 
     if ( kinfo.dom0less_feature & DOM0LESS_XENSTORE )
     {
+        struct page_info *magic_pg;
+        mfn_t mfn;
+        gfn_t gfn;
+
         ASSERT(hardware_domain);
         rc = alloc_xenstore_evtchn(d);
         if ( rc < 0 )
             return rc;
         d->arch.hvm.params[HVM_PARAM_STORE_PFN] = ~0ULL;
+
+        d->max_pages += NR_MAGIC_PAGES;
+        magic_pg = alloc_domheap_pages(d, 
get_order_from_pages(NR_MAGIC_PAGES), 0);
+        if ( magic_pg == NULL )
+            return -ENOMEM;
+
+        mfn = page_to_mfn(magic_pg);
+        if ( !is_domain_direct_mapped(d) )
+            gfn = gaddr_to_gfn(GUEST_MAGIC_BASE);
+        else
+            gfn = gaddr_to_gfn(mfn_to_maddr(mfn));
+
+        rc = guest_physmap_add_pages(d, gfn, mfn, NR_MAGIC_PAGES);
+        if ( rc )
+        {
+            free_domheap_pages(magic_pg, get_order_from_pages(NR_MAGIC_PAGES));
+            return rc;
+        }
     }
 
     return rc;
diff --git a/xen/include/public/arch-arm.h b/xen/include/public/arch-arm.h
index e167e14f8d..f24e7bbe37 100644
--- a/xen/include/public/arch-arm.h
+++ b/xen/include/public/arch-arm.h
@@ -475,6 +475,7 @@ typedef uint64_t xen_callback_t;
 
 #define GUEST_MAGIC_BASE  xen_mk_ullong(0x39000000)
 #define GUEST_MAGIC_SIZE  xen_mk_ullong(0x01000000)
+#define NR_MAGIC_PAGES 4
 
 #define GUEST_RAM_BANKS   2
 
-- 
2.34.1