[Xen-devel] [PATCH v5] boot allocator: Use arch helper for virt_to_mfn on DIRECTMAP_VIRT region

[vijay.kilari@xxxxxxxxx]

From: Vijaya Kumar K <Vijaya.Kumar@xxxxxxxxxx>

On ARM platforms with NUMA, while initializing second memory node,
panic is triggered from init_node_heap() when virt_to_mfn()
is called for DIRECTMAP_VIRT region address because DIRECTMAP_VIRT
region is not mapped to any virtual address.

The check virt_to_mfn() here is used to know whether the max MFN is
part of the direct mapping. The max MFN is found by calling virt_to_mfn
on end address of DIRECTMAP_VIRT region, which is DIRECTMAP_VIRT_END.

On ARM64, all RAM is currently direct mapped in Xen and virt_to_mfn
uses the hardware for address translation. So if the virtual address
is not mapped translation fault is raised.

In this patch, instead of calling virt_to_mfn(), arch helper
arch_mfn_in_directmap() is introduced.

On ARM64 this arch helper will return true, because currently all RAM
is direct mapped in Xen.
On ARM32, Only a limited amount of RAM, called xenheap, is always mapped
and DIRECTMAP_VIRT region is not mapped. Hence return false.
For x86 this helper does virt_to_mfn.

Signed-off-by: Vijaya Kumar K <Vijaya.Kumar@xxxxxxxxxx>
Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
---
v5: - Rewritten commit message.
    - Update comments
    - Dropped extra brackets
---
 xen/common/page_alloc.c        |  9 ++-------
 xen/include/asm-arm/arm32/mm.h | 23 +++++++++++++++++++++++
 xen/include/asm-arm/arm64/mm.h | 23 +++++++++++++++++++++++
 xen/include/asm-arm/mm.h       |  8 ++++++++
 xen/include/asm-x86/mm.h       | 11 +++++++++++
 5 files changed, 67 insertions(+), 7 deletions(-)

diff --git a/xen/common/page_alloc.c b/xen/common/page_alloc.c
index 68dba19..9e41fb4 100644
--- a/xen/common/page_alloc.c
+++ b/xen/common/page_alloc.c
@@ -520,9 +520,6 @@ static unsigned long init_node_heap(int node, unsigned long 
mfn,
     unsigned long needed = (sizeof(**_heap) +
                             sizeof(**avail) * NR_ZONES +
                             PAGE_SIZE - 1) >> PAGE_SHIFT;
-#ifdef DIRECTMAP_VIRT_END
-    unsigned long eva = min(DIRECTMAP_VIRT_END, HYPERVISOR_VIRT_END);
-#endif
     int i, j;
 
     if ( !first_node_initialised )
@@ -532,9 +529,8 @@ static unsigned long init_node_heap(int node, unsigned long 
mfn,
         first_node_initialised = 1;
         needed = 0;
     }
-#ifdef DIRECTMAP_VIRT_END
     else if ( *use_tail && nr >= needed &&
-              (mfn + nr) <= (virt_to_mfn(eva - 1) + 1) &&
+              arch_mfn_in_directmap(mfn + nr) &&
               (!xenheap_bits ||
                !((mfn + nr - 1) >> (xenheap_bits - PAGE_SHIFT))) )
     {
@@ -543,7 +539,7 @@ static unsigned long init_node_heap(int node, unsigned long 
mfn,
                       PAGE_SIZE - sizeof(**avail) * NR_ZONES;
     }
     else if ( nr >= needed &&
-              (mfn + needed) <= (virt_to_mfn(eva - 1) + 1) &&
+              arch_mfn_in_directmap(mfn + needed) &&
               (!xenheap_bits ||
                !((mfn + needed - 1) >> (xenheap_bits - PAGE_SHIFT))) )
     {
@@ -552,7 +548,6 @@ static unsigned long init_node_heap(int node, unsigned long 
mfn,
                       PAGE_SIZE - sizeof(**avail) * NR_ZONES;
         *use_tail = 0;
     }
-#endif
     else if ( get_order_from_bytes(sizeof(**_heap)) ==
               get_order_from_pages(needed) )
     {
diff --git a/xen/include/asm-arm/arm32/mm.h b/xen/include/asm-arm/arm32/mm.h
new file mode 100644
index 0000000..6861249
--- /dev/null
+++ b/xen/include/asm-arm/arm32/mm.h
@@ -0,0 +1,23 @@
+#ifndef __ARM_ARM32_MM_H__
+#define __ARM_ARM32_MM_H__
+
+/*
+ * Only a limited amount of RAM, called xenheap, is always mapped on ARM32.
+ * For convenience always return false.
+ */
+static inline bool arch_mfn_in_directmap(unsigned long mfn)
+{
+    return false;
+}
+
+#endif /* __ARM_ARM32_MM_H__ */
+
+/*
+ * Local variables:
+ * mode: C
+ * c-file-style: "BSD"
+ * c-basic-offset: 4
+ * tab-width: 4
+ * indent-tabs-mode: nil
+ * End:
+ */
diff --git a/xen/include/asm-arm/arm64/mm.h b/xen/include/asm-arm/arm64/mm.h
new file mode 100644
index 0000000..d0a3be7
--- /dev/null
+++ b/xen/include/asm-arm/arm64/mm.h
@@ -0,0 +1,23 @@
+#ifndef __ARM_ARM64_MM_H__
+#define __ARM_ARM64_MM_H__
+
+/*
+ * On ARM64, all the RAM is currently direct mapped in Xen.
+ * Hence return always true.
+ */
+static inline bool arch_mfn_in_directmap(unsigned long mfn)
+{
+    return true;
+}
+
+#endif /* __ARM_ARM64_MM_H__ */
+
+/*
+ * Local variables:
+ * mode: C
+ * c-file-style: "BSD"
+ * c-basic-offset: 4
+ * tab-width: 4
+ * indent-tabs-mode: nil
+ * End:
+ */
diff --git a/xen/include/asm-arm/mm.h b/xen/include/asm-arm/mm.h
index 4892155..0fef612 100644
--- a/xen/include/asm-arm/mm.h
+++ b/xen/include/asm-arm/mm.h
@@ -6,6 +6,14 @@
 #include <public/xen.h>
 #include <xen/pdx.h>
 
+#if defined(CONFIG_ARM_32)
+# include <asm/arm32/mm.h>
+#elif defined(CONFIG_ARM_64)
+# include <asm/arm64/mm.h>
+#else
+# error "unknown ARM variant"
+#endif
+
 /* Align Xen to a 2 MiB boundary. */
 #define XEN_PADDR_ALIGN (1 << 21)
 
diff --git a/xen/include/asm-x86/mm.h b/xen/include/asm-x86/mm.h
index e22603c..119d7de 100644
--- a/xen/include/asm-x86/mm.h
+++ b/xen/include/asm-x86/mm.h
@@ -602,4 +602,15 @@ extern const char zero_page[];
 /* Build a 32bit PSE page table using 4MB pages. */
 void write_32bit_pse_identmap(uint32_t *l2);
 
+/*
+ * x86 maps part of physical memory via the directmap region.
+ * Return whether the input MFN falls in that range.
+ */
+static inline bool arch_mfn_in_directmap(unsigned long mfn)
+{
+    unsigned long eva = min(DIRECTMAP_VIRT_END, HYPERVISOR_VIRT_END);
+
+    return mfn <= (virt_to_mfn(eva - 1) + 1);
+}
+
 #endif /* __ASM_X86_MM_H__ */
-- 
2.7.4


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