On 01/16/2017 09:39 PM, David Miller wrote:
From: Khalid Aziz <khalid.aziz@xxxxxxxxxx>
Date: Wed, 11 Jan 2017 09:12:54 -0700
diff --git a/arch/sparc/kernel/mdesc.c b/arch/sparc/kernel/mdesc.c
index 8a6982d..68b03bf 100644
--- a/arch/sparc/kernel/mdesc.c
+++ b/arch/sparc/kernel/mdesc.c
@@ -20,6 +20,7 @@
#include <asm/uaccess.h>
#include <asm/oplib.h>
#include <asm/smp.h>
+#include <asm/adi.h>
/* Unlike the OBP device tree, the machine description is a full-on
* DAG. An arbitrary number of ARCs are possible from one
@@ -1104,5 +1105,8 @@ void __init sun4v_mdesc_init(void)
cur_mdesc = hp;
+#ifdef CONFIG_SPARC64
mdesc.c is only built on sparc64, this ifdef is superfluous.
Good point. I will fix it.
+/* Update the state of MCDPER register in current task's mm context before
+ * dup so the dup'd task will inherit flags in this register correctly.
+ * Current task may have updated flags since it started running.
+ */
+int arch_dup_task_struct(struct task_struct *dst, struct task_struct *src)
+{
+ if (adi_capable() && src->mm) {
+ register unsigned long tmp_mcdper;
+
+ __asm__ __volatile__(
+ ".word 0x83438000\n\t" /* rd %mcdper, %g1 */
+ "mov %%g1, %0\n\t"
+ : "=r" (tmp_mcdper)
+ :
+ : "g1");
+ src->mm->context.mcdper = tmp_mcdper;
I don't like the idea of duplicating 'mm' state using the task struct
copy. Why do not the MM handling interfaces handle this properly?
Maybe it means you've abstracted the ADI register handling in the
wrong place. Maybe it's a thread property which is "pushed" from
the MM context.
I see what you are saying. This code updates mm->context.mcdper for the
source thread with the current state of MCDPER since MCDPER can be
changed by a userspace process any time. When userspace changes MCDPER,
it is not saved into mm->context.mcdper until a context switch happens.
This means during the timeslice for a thread, its mm->context.mcdper may
not reflect the current value of MCDPER. Updating it ensures dup_mm()
will copy the real current value of MCDPER into the newly forked thread.
arch_dup_mmap() looks like a more appropriate place to do this. Do you
agree?
Thanks,
Khalid
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