[Xen-devel] [PATCH v2 1/2] xen/link: Introduce .bss.percpu.page_aligned

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

Future changes are going to need to page align some percpu data.

This means that the percpu area needs suitably aligning in the BSS so CPU0 has
correctly aligned data.  Shuffle the exact link order of items within the BSS
to give .bss.percpu.page_aligned appropriate alignment.

In addition, we need to be able to specify an alignment attribute to
__DEFINE_PER_CPU().  Rework it so the caller passes in all attributes, and
adjust DEFINE_PER_CPU{,_READ_MOSTLY}() to match.  This has the added bonus
that it is now possible to grep for .bss.percpu and find all the users.

Finally, introduce DEFINE_PER_CPU_PAGE_ALIGNED() which uses both section and
alignment attributes.

Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
---
CC: Jan Beulich <JBeulich@xxxxxxxx>
CC: Wei Liu <wl@xxxxxxx>
CC: Roger Pau Monné <roger.pau@xxxxxxxxxx>
CC: Stefano Stabellini <sstabellini@xxxxxxxxxx>
CC: Julien Grall <julien.grall@xxxxxxx>
CC: Volodymyr Babchuk <Volodymyr_Babchuk@xxxxxxxx>

v2:
 * Rework __DEFINE_PER_CPU() to allow for further attributes to be passed.
 * Specify __aligned(PAGE_SIZE) as part of DEFINE_PER_CPU_PAGE_ALIGNED().
---
 xen/arch/arm/xen.lds.S       |  5 +++--
 xen/arch/x86/xen.lds.S       |  5 +++--
 xen/include/asm-arm/percpu.h |  6 ++----
 xen/include/asm-x86/percpu.h |  6 ++----
 xen/include/xen/percpu.h     | 10 ++++++++--
 5 files changed, 18 insertions(+), 14 deletions(-)

diff --git a/xen/arch/arm/xen.lds.S b/xen/arch/arm/xen.lds.S
index 12c107f45d..07cbdf2543 100644
--- a/xen/arch/arm/xen.lds.S
+++ b/xen/arch/arm/xen.lds.S
@@ -201,14 +201,15 @@ SECTIONS
        *(.bss.stack_aligned)
        . = ALIGN(PAGE_SIZE);
        *(.bss.page_aligned)
-       *(.bss)
-       . = ALIGN(SMP_CACHE_BYTES);
        __per_cpu_start = .;
+       *(.bss.percpu.page_aligned)
        *(.bss.percpu)
        . = ALIGN(SMP_CACHE_BYTES);
        *(.bss.percpu.read_mostly)
        . = ALIGN(SMP_CACHE_BYTES);
        __per_cpu_data_end = .;
+       *(.bss)
+       . = ALIGN(SMP_CACHE_BYTES);
        __bss_end = .;
   } :text
   _end = . ;
diff --git a/xen/arch/x86/xen.lds.S b/xen/arch/x86/xen.lds.S
index a73139cd29..b8a2ea4259 100644
--- a/xen/arch/x86/xen.lds.S
+++ b/xen/arch/x86/xen.lds.S
@@ -293,14 +293,15 @@ SECTIONS
        __bss_start = .;
        *(.bss.stack_aligned)
        *(.bss.page_aligned*)
-       *(.bss)
-       . = ALIGN(SMP_CACHE_BYTES);
        __per_cpu_start = .;
+       *(.bss.percpu.page_aligned)
        *(.bss.percpu)
        . = ALIGN(SMP_CACHE_BYTES);
        *(.bss.percpu.read_mostly)
        . = ALIGN(SMP_CACHE_BYTES);
        __per_cpu_data_end = .;
+       *(.bss)
+       . = ALIGN(SMP_CACHE_BYTES);
        __bss_end = .;
   } :text
   _end = . ;
diff --git a/xen/include/asm-arm/percpu.h b/xen/include/asm-arm/percpu.h
index 9584b830d4..264120b192 100644
--- a/xen/include/asm-arm/percpu.h
+++ b/xen/include/asm-arm/percpu.h
@@ -10,10 +10,8 @@ extern char __per_cpu_start[], __per_cpu_data_end[];
 extern unsigned long __per_cpu_offset[NR_CPUS];
 void percpu_init_areas(void);
 
-/* Separate out the type, so (int[3], foo) works. */
-#define __DEFINE_PER_CPU(type, name, suffix)                    \
-    __section(".bss.percpu" #suffix)                            \
-    __typeof__(type) per_cpu_##name
+#define __DEFINE_PER_CPU(attr, type, name) \
+    attr __typeof__(type) per_cpu_ ## name
 
 #define per_cpu(var, cpu)  \
     (*RELOC_HIDE(&per_cpu__##var, __per_cpu_offset[cpu]))
diff --git a/xen/include/asm-x86/percpu.h b/xen/include/asm-x86/percpu.h
index ff34dc7897..5b6cef04c4 100644
--- a/xen/include/asm-x86/percpu.h
+++ b/xen/include/asm-x86/percpu.h
@@ -7,10 +7,8 @@ extern unsigned long __per_cpu_offset[NR_CPUS];
 void percpu_init_areas(void);
 #endif
 
-/* Separate out the type, so (int[3], foo) works. */
-#define __DEFINE_PER_CPU(type, name, suffix)                    \
-    __section(".bss.percpu" #suffix)                            \
-    __typeof__(type) per_cpu_##name
+#define __DEFINE_PER_CPU(attr, type, name) \
+    attr __typeof__(type) per_cpu_ ## name
 
 /* var is in discarded region: offset to particular copy we want */
 #define per_cpu(var, cpu)  \
diff --git a/xen/include/xen/percpu.h b/xen/include/xen/percpu.h
index aeec5c19d6..71a31cc361 100644
--- a/xen/include/xen/percpu.h
+++ b/xen/include/xen/percpu.h
@@ -9,9 +9,15 @@
  * The _##name concatenation is being used here to prevent 'name' from getting
  * macro expanded, while still allowing a per-architecture symbol name prefix.
  */
-#define DEFINE_PER_CPU(type, name) __DEFINE_PER_CPU(type, _##name, )
+#define DEFINE_PER_CPU(type, name) \
+    __DEFINE_PER_CPU(__section(".bss.percpu"), type, _ ## name)
+
+#define DEFINE_PER_CPU_PAGE_ALIGNED(type, name) \
+    __DEFINE_PER_CPU(__section(".bss.percpu.page_aligned") \
+                     __aligned(PAGE_SIZE), type, _ ## name)
+
 #define DEFINE_PER_CPU_READ_MOSTLY(type, name) \
-       __DEFINE_PER_CPU(type, _##name, .read_mostly)
+    __DEFINE_PER_CPU(__section(".bss.percpu.read_mostly"), type, _ ## name)
 
 #define get_per_cpu_var(var)  (per_cpu__##var)
 
-- 
2.11.0


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