Re: [PATCH v6 5/9] xen/asm-generic: introduce stub header numa.h

[Jan Beulich <jbeulich@xxxxxxxx>]

On 22.12.2023 14:07, Oleksii wrote:
> On Fri, 2023-12-22 at 09:22 +0100, Jan Beulich wrote:
>> On 21.12.2023 20:09, Julien Grall wrote:
>>> On 20/12/2023 14:08, Oleksii Kurochko wrote:
>>>> <asm/numa.h> is common through some archs so it is moved
>>>> to asm-generic.
>>>>
>>>> Signed-off-by: Oleksii Kurochko <oleksii.kurochko@xxxxxxxxx>
>>>> Reviewed-by: Michal Orzel <michal.orzel@xxxxxxx>
>>>> Acked-by: Jan Beulich <jbeulich@xxxxxxxx>
>>>> Acked-by: Shawn Anastasio <sanastasio@xxxxxxxxxxxxxxxxxxxxx>
>>>
>>> I think this patch will need to be rebased on top of the lastest
>>> staging 
>>> as this should clash with 51ffb3311895.
>>
>> No, and I'd like to withdraw my ack here. In this case a stub header
>> isn't
>> the right choice imo - the !NUMA case should be handled in common
>> code. I
>> would have submitted the patch I have, if only the first_valid_mfn
>> patch
>> hadn't been committed already (which I now need to re-base over).
> I haven't seen your patch yet (waiting for it), but I assume that
> <asm/numa.h> will still be necessary and remain the same across Arm,
> PPC, and RISC-V.
> 
> What am I missing?

asm/numa.h will be necessary for an arch only if it actually has a way
to have CONFIG_NUMA enabled. Below, for your reference, the patch in
the not-yet-rebased form. As you can see, Arm's (and PPC's) header goes
away. If and when they choose to support NUMA, they may need to regain
one; whether at that point we can sort how an asm-generic/ form of the
header might sensibly look like remains to be seen.

Jan

NUMA: no need for asm/numa.h when !NUMA

There's no point in every architecture carrying the same stubs for the
case when NUMA isn't enabled (or even supported). Move all of that to
xen/numa.h; replace explicit uses of asm/numa.h in common code. Make
inclusion of asm/numa.h dependent upon NUMA=y.

Address the TODO regarding first_valid_mfn by making the variable static
when NUMA=y, thus also addressing a Misrs C:2012 rule 8.4 concern. Drop
the not really applicable "implement NUMA support" comment - in a !NUMA
section this simply makes no sense.

Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
---
This is an alternative proposal to
https://lists.xen.org/archives/html/xen-devel/2023-12/msg01586.html
and its earlier forms.

--- unstable.orig/xen/arch/arm/include/asm/numa.h
+++ /dev/null
@@ -1,37 +0,0 @@
-#ifndef __ARCH_ARM_NUMA_H
-#define __ARCH_ARM_NUMA_H
-
-#include <xen/mm.h>
-
-typedef u8 nodeid_t;
-
-#ifndef CONFIG_NUMA
-
-/* Fake one node for now. See also node_online_map. */
-#define cpu_to_node(cpu) 0
-#define node_to_cpumask(node)   (cpu_online_map)
-
-/*
- * TODO: make first_valid_mfn static when NUMA is supported on Arm, this
- * is required because the dummy helpers are using it.
- */
-extern mfn_t first_valid_mfn;
-
-/* XXX: implement NUMA support */
-#define node_spanned_pages(nid) (max_page - mfn_x(first_valid_mfn))
-#define node_start_pfn(nid) (mfn_x(first_valid_mfn))
-#define __node_distance(a, b) (20)
-
-#endif
-
-#define arch_want_default_dmazone() (false)
-
-#endif /* __ARCH_ARM_NUMA_H */
-/*
- * Local variables:
- * mode: C
- * c-file-style: "BSD"
- * c-basic-offset: 4
- * indent-tabs-mode: nil
- * End:
- */
--- unstable.orig/xen/arch/arm/smpboot.c
+++ unstable/xen/arch/arm/smpboot.c
@@ -42,7 +42,7 @@ integer_param("maxcpus", max_cpus);
 /* CPU logical map: map xen cpuid to an MPIDR */
 register_t __cpu_logical_map[NR_CPUS] = { [0 ... NR_CPUS-1] = MPIDR_INVALID };
 
-/* Fake one node for now. See also asm/numa.h */
+/* Fake one node for now. See also xen/numa.h */
 nodemask_t __read_mostly node_online_map = { { [0] = 1UL } };
 
 /* Xen stack for bringing up the first CPU. */
--- unstable.orig/xen/arch/ppc/include/asm/numa.h
+++ /dev/null
@@ -1,26 +0,0 @@
-#ifndef __ASM_PPC_NUMA_H__
-#define __ASM_PPC_NUMA_H__
-
-#include <xen/types.h>
-#include <xen/mm.h>
-
-typedef uint8_t nodeid_t;
-
-/* Fake one node for now. See also node_online_map. */
-#define cpu_to_node(cpu) 0
-#define node_to_cpumask(node)   (cpu_online_map)
-
-/*
- * TODO: make first_valid_mfn static when NUMA is supported on PPC, this
- * is required because the dummy helpers are using it.
- */
-extern mfn_t first_valid_mfn;
-
-/* XXX: implement NUMA support */
-#define node_spanned_pages(nid) (max_page - mfn_x(first_valid_mfn))
-#define node_start_pfn(nid) (mfn_x(first_valid_mfn))
-#define __node_distance(a, b) (20)
-
-#define arch_want_default_dmazone() (false)
-
-#endif /* __ASM_PPC_NUMA_H__ */
--- unstable.orig/xen/common/page_alloc.c
+++ unstable/xen/common/page_alloc.c
@@ -140,7 +140,6 @@
 #include <xen/vm_event.h>
 
 #include <asm/flushtlb.h>
-#include <asm/numa.h>
 #include <asm/page.h>
 
 #include <public/sysctl.h>
@@ -256,10 +255,14 @@ static PAGE_LIST_HEAD(page_broken_list);
  * BOOT-TIME ALLOCATOR
  */
 
+#ifndef CONFIG_NUMA
 /*
  * first_valid_mfn is exported because it is use in ARM specific NUMA
  * helpers. See comment in arch/arm/include/asm/numa.h.
  */
+#else
+static
+#endif
 mfn_t first_valid_mfn = INVALID_MFN_INITIALIZER;
 
 struct bootmem_region {
--- unstable.orig/xen/common/sysctl.c
+++ unstable/xen/common/sysctl.c
@@ -22,8 +22,8 @@
 #include <asm/current.h>
 #include <xen/hypercall.h>
 #include <public/sysctl.h>
-#include <asm/numa.h>
 #include <xen/nodemask.h>
+#include <xen/numa.h>
 #include <xsm/xsm.h>
 #include <xen/pmstat.h>
 #include <xen/livepatch.h>
--- unstable.orig/xen/include/xen/domain.h
+++ unstable/xen/include/xen/domain.h
@@ -2,6 +2,7 @@
 #ifndef __XEN_DOMAIN_H__
 #define __XEN_DOMAIN_H__
 
+#include <xen/numa.h>
 #include <xen/types.h>
 
 #include <public/xen.h>
@@ -12,7 +13,6 @@ struct guest_area {
 };
 
 #include <asm/domain.h>
-#include <asm/numa.h>
 
 typedef union {
     struct vcpu_guest_context *nat;
--- unstable.orig/xen/include/xen/numa.h
+++ unstable/xen/include/xen/numa.h
@@ -2,7 +2,13 @@
 #define _XEN_NUMA_H
 
 #include <xen/mm-frame.h>
+
+#ifdef CONFIG_NUMA
+#include <xen/pdx.h>
 #include <asm/numa.h>
+#else
+typedef uint8_t nodeid_t;
+#endif
 
 #define NUMA_NO_NODE     0xFF
 #define NUMA_NO_DISTANCE 0xFF
@@ -108,6 +114,18 @@ extern void numa_set_processor_nodes_par
 
 #else
 
+/* Fake one node for now. See also node_online_map. */
+#define cpu_to_node(cpu) 0
+#define node_to_cpumask(node)   cpu_online_map
+
+#define arch_want_default_dmazone() false
+
+extern mfn_t first_valid_mfn;
+
+#define node_spanned_pages(nid) (max_page - mfn_x(first_valid_mfn))
+#define node_start_pfn(nid) mfn_x(first_valid_mfn)
+#define __node_distance(a, b) 20
+
 static inline nodeid_t mfn_to_nid(mfn_t mfn)
 {
     return 0;
--- unstable.orig/xen/include/xen/pci.h
+++ unstable/xen/include/xen/pci.h
@@ -11,10 +11,10 @@
 #include <xen/list.h>
 #include <xen/spinlock.h>
 #include <xen/irq.h>
+#include <xen/numa.h>
 #include <xen/pci_regs.h>
 #include <xen/pfn.h>
 #include <asm/device.h>
-#include <asm/numa.h>
 
 /*
  * The PCI interface treats multi-function devices as independent