[PATCH] xen/common: Do not allocate magic pages 1:1 for direct mapped domains

[Henry Wang <xin.wang2@xxxxxxx>]

An error message can seen from the init-dom0less application on
direct-mapped 1:1 domains:
```
Allocating magic pages
memory.c:238:d0v0 mfn 0x39000 doesn't belong to d1
Error on alloc magic pages
```

This is because populate_physmap() automatically assumes gfn == mfn
for direct mapped domains. This cannot be true for the magic pages
that are allocated later for Dom0less DomUs from the init-dom0less
helper application executed in Dom0.

Force populate_physmap to take the "normal" memory allocation route for
the magic pages even for 1:1 Dom0less DomUs. This should work as long
as the 1:1 Dom0less DomU doesn't have anything else mapped at the same
guest address as the magic pages:
- gfn 0x39000 address 0x39000000
- gfn 0x39001 address 0x39001000
- gfn 0x39002 address 0x39002000
- gfn 0x39003 address 0x39003000
Create helper is_magic_gpfn() for Arm to assist this and stub helpers
for non-Arm architectures to avoid #ifdef. Move the definition of the
magic pages on Arm to a more common place.

Note that the init-dom0less application of the diffenent Xen version
may allocate all or part of four magic pages for each DomU.

Reported-by: Alec Kwapis <alec.kwapis@xxxxxxxxxxxxx>
Signed-off-by: Stefano Stabellini <sstabellini@xxxxxxxxxx>
Signed-off-by: Henry Wang <xin.wang2@xxxxxxx>
---
 tools/libs/guest/xg_dom_arm.c   |  6 ------
 xen/arch/arm/include/asm/mm.h   | 13 +++++++++++++
 xen/arch/ppc/include/asm/mm.h   |  5 +++++
 xen/arch/riscv/include/asm/mm.h |  6 ++++++
 xen/arch/x86/include/asm/mm.h   |  5 +++++
 xen/common/memory.c             |  2 +-
 xen/include/public/arch-arm.h   |  6 ++++++
 7 files changed, 36 insertions(+), 7 deletions(-)

diff --git a/tools/libs/guest/xg_dom_arm.c b/tools/libs/guest/xg_dom_arm.c
index 2fd8ee7ad4..8c579d7576 100644
--- a/tools/libs/guest/xg_dom_arm.c
+++ b/tools/libs/guest/xg_dom_arm.c
@@ -25,12 +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
-#define VUART_PFN_OFFSET 3
-
 #define LPAE_SHIFT 9
 
 #define PFN_4K_SHIFT  (0)
diff --git a/xen/arch/arm/include/asm/mm.h b/xen/arch/arm/include/asm/mm.h
index cbcf3bf147..17149b4635 100644
--- a/xen/arch/arm/include/asm/mm.h
+++ b/xen/arch/arm/include/asm/mm.h
@@ -428,6 +428,19 @@ static inline void page_set_xenheap_gfn(struct page_info 
*p, gfn_t gfn)
     } while ( (y = cmpxchg(&p->u.inuse.type_info, x, nx)) != x );
 }
 
+#define MAGIC_PAGE_N_GPFN(n)     ((GUEST_MAGIC_BASE >> PAGE_SHIFT) + n)
+static inline bool is_magic_gpfn(xen_pfn_t gpfn)
+{
+    unsigned int i;
+    for ( i = 0; i < NR_MAGIC_PAGES; i++ )
+    {
+        if ( gpfn == MAGIC_PAGE_N_GPFN(i) )
+            return true;
+    }
+
+    return false;
+}
+
 #endif /*  __ARCH_ARM_MM__ */
 /*
  * Local variables:
diff --git a/xen/arch/ppc/include/asm/mm.h b/xen/arch/ppc/include/asm/mm.h
index a433936076..8ad81d9552 100644
--- a/xen/arch/ppc/include/asm/mm.h
+++ b/xen/arch/ppc/include/asm/mm.h
@@ -256,4 +256,9 @@ static inline bool arch_mfns_in_directmap(unsigned long 
mfn, unsigned long nr)
     return true;
 }
 
+static inline bool is_magic_gpfn(xen_pfn_t gpfn)
+{
+    return false;
+}
+
 #endif /* _ASM_PPC_MM_H */
diff --git a/xen/arch/riscv/include/asm/mm.h b/xen/arch/riscv/include/asm/mm.h
index 07c7a0abba..a376a77e29 100644
--- a/xen/arch/riscv/include/asm/mm.h
+++ b/xen/arch/riscv/include/asm/mm.h
@@ -3,6 +3,7 @@
 #ifndef _ASM_RISCV_MM_H
 #define _ASM_RISCV_MM_H
 
+#include <public/xen.h>
 #include <asm/page-bits.h>
 
 #define pfn_to_paddr(pfn) ((paddr_t)(pfn) << PAGE_SHIFT)
@@ -20,4 +21,9 @@ unsigned long calc_phys_offset(void);
 
 void turn_on_mmu(unsigned long ra);
 
+static inline bool is_magic_gpfn(xen_pfn_t gpfn)
+{
+    return false;
+}
+
 #endif /* _ASM_RISCV_MM_H */
diff --git a/xen/arch/x86/include/asm/mm.h b/xen/arch/x86/include/asm/mm.h
index 7d26d9cd2f..f385f36d78 100644
--- a/xen/arch/x86/include/asm/mm.h
+++ b/xen/arch/x86/include/asm/mm.h
@@ -628,4 +628,9 @@ static inline bool arch_mfns_in_directmap(unsigned long 
mfn, unsigned long nr)
     return (mfn + nr) <= (virt_to_mfn(eva - 1) + 1);
 }
 
+static inline bool is_magic_gpfn(xen_pfn_t gpfn)
+{
+    return false;
+}
+
 #endif /* __ASM_X86_MM_H__ */
diff --git a/xen/common/memory.c b/xen/common/memory.c
index b3b05c2ec0..ab4bad79e2 100644
--- a/xen/common/memory.c
+++ b/xen/common/memory.c
@@ -219,7 +219,7 @@ static void populate_physmap(struct memop_args *a)
         }
         else
         {
-            if ( is_domain_direct_mapped(d) )
+            if ( is_domain_direct_mapped(d) && !is_magic_gpfn(gpfn) )
             {
                 mfn = _mfn(gpfn);
 
diff --git a/xen/include/public/arch-arm.h b/xen/include/public/arch-arm.h
index a25e87dbda..58aa6ff05b 100644
--- a/xen/include/public/arch-arm.h
+++ b/xen/include/public/arch-arm.h
@@ -476,6 +476,12 @@ 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 CONSOLE_PFN_OFFSET 0
+#define XENSTORE_PFN_OFFSET 1
+#define MEMACCESS_PFN_OFFSET 2
+#define VUART_PFN_OFFSET 3
+
 #define GUEST_RAM_BANKS   2
 
 /*
-- 
2.34.1