Michal Such=C3=A1nek [off-list ref] writes:

Hello,

On Sun, 19 Feb 2017 15:37:15 +0530
"Aneesh Kumar K.V" [off-list ref] wrote:

quoted

We update the hash linux page table layout such that we can support
512TB. But we limit the TASK_SIZE to 128TB. We can switch to 128TB by
default without conditional because that is the max virtual address
supported by other architectures. We will later add a mechanism to
on-demand increase the application's effective address range to 512TB.
=20
Having the page table layout changed to accommodate 512TB  makes
testing large memory configuration easier with less code changes to
kernel
=20
Signed-off-by: Aneesh Kumar K.V <redacted>

....

index b64daf124fee..c7ca70dc3ba5 100644

quoted

--- a/arch/powerpc/kernel/paca.c
+++ b/arch/powerpc/kernel/paca.c

@@ -253,8 +253,15 @@ void copy_mm_to_paca(struct mm_struct *mm)
 	get_paca()->mm_ctx_id =3D context->id;
 #ifdef CONFIG_PPC_MM_SLICES
 	get_paca()->mm_ctx_low_slices_psize =3D

context->low_slices_psize;
+	/*
+	 * We support upto 128TB for now. Hence copy only 128/2
bytes.
+	 * Later when we support tasks with different max effective
+	 * address, we can optimize this based on mm->task_size.
+	 */
+	BUILD_BUG_ON(TASK_SIZE_USER64 !=3D TASK_SIZE_128TB);

Can this be handled by KConfig?
Above I see=20

I am reworking the series so that we depend on mm->task_size. Will send
a new version soon.

quoted

+#ifdef CONFIG_PPC_BOOK3S_64
+#define TASK_SIZE_USER64 TASK_SIZE_128TB
+#else
+#define TASK_SIZE_USER64 TASK_SIZE_64TB
+#endif

and=20

quoted

#ifdef CONFIG_PPC_MM_SLICES
ILD_BUG_ON(TASK_SIZE_USER64 !=3D TASK_SIZE_128TB)

which boils down to
#ifndef CONFIG_PPC_BOOK3S_64
#ifdef CONFIG_PPC_MM_SLICES
#error TASK_SIZE_USER64 !=3D TASK_SIZE_128TB

quoted

 	memcpy(&get_paca()->mm_ctx_high_slices_psize,
-	       &context->high_slices_psize, SLICE_ARRAY_SIZE);
+	       &context->high_slices_psize, TASK_SIZE_128TB >> 41);

Can we avoid magic numbers, please?

Since array is 4 bytes per each TB which is documented else where.
Considering we are just converting max range there, do we need that as a
macro ?

-aneesh