[C/R ARM][PATCH 3/3] c/r: ARM implementation of checkpoint/restart

On Tue, Mar 23, 2010 at 5:09 PM, Serge E. Hallyn [off-list ref] wrote:

Quoting Christoffer Dall (christofferdall at christofferdall.dk):

quoted

Implements architecture specific requirements for checkpoint/restart on
ARM. The changes touch almost only c/r related code. Most of the work is
done in arch/arm/checkpoint.c, which implements checkpointing of the CPU
and necessary fields on the thread_info struct.

The ISA version (given by __LINUX_ARM_ARCH__) is checkpointed and verified
against the machine architecture on restart. If they differ, an error is
raised and restart aborted. It should be possible to restart on newer
architectures, but further investigation is warranted.

Regarding ThumbEE, the thumbee_state field on the thread_info is stored
in checkpoints when CONFIG_ARM_THUMBEE and 0 is stored otherwise. If
a value different than 0 is checkpointed and CONFIG_ARM_THUMBEE is not
set on the restore system, the restore is aborted. Feedback on this
implementation is very welcome.

We checkpoint whether the system is running with CONFIG_MMU or not and
require the same configuration for the system on which we restore the
process. It might be possible to allow something more fine-grained,
if it's worth the energy. Input on this item is also very welcome,
specifically from someone who knows the exact meaning of the end_brk
field.

Added support for syscall sys_checkpoint and sys_restart for ARM:
__NR_checkpoint ? ? ? ? 367
__NR_restart ? ? ? ? ? ?368


Cc: rmk at arm.linux.org.uk
Signed-off-by: Christoffer Dall <redacted>
Acked-by: Oren Laadan <redacted>

In terms of the cr api I don't see any problems. ?Two nits below,
but in any case

Acked-by: Serge Hallyn <redacted>

thanks, this is really cool, especially how minimal it is :)
-serge

thanks

...

quoted

+static int load_cpu_regs(struct ckpt_hdr_cpu *h, struct task_struct *t)
+{
+ ? ? int i;
+ ? ? struct pt_regs *regs = task_pt_regs(t);
+
+ ? ? memcpy(regs, &h->uregs, sizeof(struct pt_regs));
+
+ ? ? for (i = 0; i < 16; i++)
+ ? ? ? ? ? ? regs->uregs[i] = h->uregs[i];
+
+ ? ? /*
+ ? ? ?* Restore only user-writable bits on the CPSR
+ ? ? ?*/
+ ? ? regs->ARM_cpsr = regs->ARM_cpsr |
+ ? ? ? ? ? ? ? ? ? ? ?(h->ARM_cpsr & (PSR_N_BIT | PSR_Z_BIT |
+ ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ?PSR_C_BIT | PSR_V_BIT |
+ ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ?PSR_V_BIT | PSR_Q_BIT |
+ ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ?PSR_E_BIT | PSR_GE_BITS));
+ ? ? regs->ARM_ORIG_r0 = h->ARM_ORIG_r0;
+
+ ? ? return 0;
+}
+
+/* read the cpu state and registers for the current task */
+int restore_cpu(struct ckpt_ctx *ctx)
+{
+ ? ? struct ckpt_hdr_cpu *h;
+ ? ? struct task_struct *t = current;
+ ? ? int ret;
+
+ ? ? h = ckpt_read_obj_type(ctx, sizeof(*h), CKPT_HDR_CPU);
+ ? ? if (IS_ERR(h))
+ ? ? ? ? ? ? return PTR_ERR(h);
+
+ ? ? ret = load_cpu_regs(h, t);

will load_cpu_regs() ever be changed to return anything but 0? ?If
not both fns can be simplified.

you're right. I will put load_cpu_regs() inline in restore_cpu.

...

quoted

+int restore_mm_context(struct ckpt_ctx *ctx, struct mm_struct *mm)
+{
+ ? ? struct ckpt_hdr_mm_context *h;
+ ? ? int ret = 0;
+
+ ? ? h = ckpt_read_obj_type(ctx, sizeof(*h), CKPT_HDR_MM_CONTEXT);
+ ? ? if (IS_ERR(h))
+ ? ? ? ? ? ? return PTR_ERR(h);
+
+#if !CONFIG_MMU
+ ? ? mm->context.end_brk = h->end_brk;
+#endif
+
+ ? ? ckpt_hdr_put(ctx, h);
+ ? ? return ret;

Again ret doesn't seem needed here.

indeed it doesn't.

-Christoffer