Subject: Re: [PATCH 2/4] powerpc: Update kernel VSID range

From: "Aneesh Kumar K.V" <[email-masked]>
Date: Thu, 14 Feb 2013 22:51:26 +0530

"Aneesh Kumar K.V" <[email-masked]> writes:

> From: "Aneesh Kumar K.V" <[email-masked]>
>
> This patch change the kernel VSID range so that we limit VSID_BITS to 37.
> This enables us to support 64TB with 65 bit VA (37+28). Without this patch
> we have boot hangs on platforms that only support 65 bit VA.
>
> With this patch we now have proto vsid generated as below:
>
> We first generate a 37-bit "proto-VSID". Proto-VSIDs are generated
> from mmu context id and effective segment id of the address.
>
> For user processes max context id is limited to ((1ul << 19) - 6)
> for kernel space, we use the top 4 context ids to map address as below
> 0x7fffb -  [ 0xc000000000000000 - 0xcfffffffffffffff ]
> 0x7fffc -  [ 0xd000000000000000 - 0xdfffffffffffffff ]
> 0x7fffd -  [ 0xe000000000000000 - 0xefffffffffffffff ]
> 0x7fffe -  [ 0xf000000000000000 - 0xffffffffffffffff ]

I guess we can do this as below

 0x7fffc -  [ 0xc000000000000000 - 0xcfffffffffffffff ]
 0x7fffd -  [ 0xd000000000000000 - 0xdfffffffffffffff ]
 0x7fffe -  [ 0xe000000000000000 - 0xefffffffffffffff ]
 0x7ffff -  [ 0xf000000000000000 - 0xffffffffffffffff ]

Will update this as part of next revision after I get full review.

diff --git a/arch/powerpc/include/asm/mmu-hash64.h b/arch/powerpc/include/asm/mmu-hash64.h
index 3e297ea..71c69e6 100644
--- a/arch/powerpc/include/asm/mmu-hash64.h
+++ b/arch/powerpc/include/asm/mmu-hash64.h
@@ -355,10 +355,10 @@ extern void slb_set_size(u16 size);
  *
  * For user processes max context id is limited to ((1ul << 19) - 6)
  * for kernel space, we use the top 4 context ids to map address as below
- * 0x7fffb -  [ 0xc000000000000000 - 0xcfffffffffffffff ]
- * 0x7fffc -  [ 0xd000000000000000 - 0xdfffffffffffffff ]
- * 0x7fffd -  [ 0xe000000000000000 - 0xefffffffffffffff ]
- * 0x7fffe -  [ 0xf000000000000000 - 0xffffffffffffffff ]
+ * 0x7fffc -  [ 0xc000000000000000 - 0xcfffffffffffffff ]
+ * 0x7fffd -  [ 0xd000000000000000 - 0xdfffffffffffffff ]
+ * 0x7fffe -  [ 0xe000000000000000 - 0xefffffffffffffff ]
+ * 0x7ffff -  [ 0xf000000000000000 - 0xffffffffffffffff ]
  *
  * The proto-VSIDs are then scrambled into real VSIDs with the
  * multiplicative hash:
@@ -561,10 +561,10 @@ static inline unsigned long get_vsid(unsigned long context, unsigned long ea,
  * This is only valid for addresses >= PAGE_OFFSET
  *
  * For kernel space, we use the top 4 context ids to map address as below
- * 0x7fffb -  [ 0xc000000000000000 - 0xcfffffffffffffff ]
- * 0x7fffc -  [ 0xd000000000000000 - 0xdfffffffffffffff ]
- * 0x7fffd -  [ 0xe000000000000000 - 0xefffffffffffffff ]
- * 0x7fffe -  [ 0xf000000000000000 - 0xffffffffffffffff ]
+ * 0x7fffc -  [ 0xc000000000000000 - 0xcfffffffffffffff ]
+ * 0x7fffd -  [ 0xd000000000000000 - 0xdfffffffffffffff ]
+ * 0x7fffe -  [ 0xe000000000000000 - 0xefffffffffffffff ]
+ * 0x7ffff -  [ 0xf000000000000000 - 0xffffffffffffffff ]
  */
 static inline unsigned long get_kernel_vsid(unsigned long ea, int ssize)
 {
@@ -574,7 +574,7 @@ static inline unsigned long get_kernel_vsid(unsigned long ea, int ssize)
 	 * kernel take the top 4 context from the available range
 	 */
 	c_index =   ((ea >> 60) - 0xc);
-	context = (MAX_CONTEXT - 4) + c_index;
+	context = (MAX_CONTEXT - 3) + c_index;
 #ifdef CONFIG_DEBUG_VM
 	/*
 	 * Drop the c_index related bits from ea, so we get
diff --git a/arch/powerpc/kernel/exceptions-64s.S b/arch/powerpc/kernel/exceptions-64s.S
index d8f6804..cb6404b 100644
--- a/arch/powerpc/kernel/exceptions-64s.S
+++ b/arch/powerpc/kernel/exceptions-64s.S
@@ -1273,10 +1273,10 @@ _GLOBAL(do_stab_bolted)
 	/*
 	 * Calculate VSID:
 	 * This is the kernel vsid, we take the top for context from
-	 * the range. context = (MAX_CONTEXT - 4) + ((ea >> 60) - 0xc)
+	 * the range. context = (MAX_CONTEXT - 3) + ((ea >> 60) - 0xc)
 	 */
 	srdi	r9,r11,60
-	subi	r9,r9,(0xc + 4 + 1)
+	subi	r9,r9,(0xc + 3 + 1)
 	lis	r10,8
 	add	r9,r9,r10		/* context */
 
diff --git a/arch/powerpc/mm/mmu_context_hash64.c b/arch/powerpc/mm/mmu_context_hash64.c
index 9c84b16..59cd773 100644
--- a/arch/powerpc/mm/mmu_context_hash64.c
+++ b/arch/powerpc/mm/mmu_context_hash64.c
@@ -48,6 +48,7 @@ again:
 		return err;
 
 	if (index > (MAX_CONTEXT - 4)) {
+		/* Top 4 context id values are used for kernel */
 		spin_lock(&mmu_context_lock);
 		ida_remove(&mmu_context_ida, index);
 		spin_unlock(&mmu_context_lock);
diff --git a/arch/powerpc/mm/slb_low.S b/arch/powerpc/mm/slb_low.S
index 2a233cb..2c9524b 100644
--- a/arch/powerpc/mm/slb_low.S
+++ b/arch/powerpc/mm/slb_low.S
@@ -56,10 +56,10 @@ _GLOBAL(slb_allocate_realmode)
 _GLOBAL(slb_miss_kernel_load_linear)
 	li	r11,0
 	/*
-	 * context = (MAX_CONTEXT - 4) + ((ea >> 60) - 0xc)
+	 * context = (MAX_CONTEXT - 3) + ((ea >> 60) - 0xc)
 	 */
 	srdi	r9,r3,60
-	subi	r9,r9,(0xc + 4 + 1)
+	subi	r9,r9,(0xc + 3 + 1)
 	lis	r10, 8
 	add	r9,r9,r10
 	srdi	r10,r3,SID_SHIFT	/* get esid */
@@ -99,10 +99,10 @@ _GLOBAL(slb_miss_kernel_load_vmemmap)
 	li	r11,0
 6:
 	/*
-	 * context = (MAX_CONTEXT - 4) + ((ea >> 60) - 0xc)
+	 * context = (MAX_CONTEXT - 3) + ((ea >> 60) - 0xc)
 	 */
 	srdi	r9,r3,60
-	subi	r9,r9,(0xc + 4 + 1)
+	subi	r9,r9,(0xc + 3 + 1)
 	lis	r10,8
 	add	r9,r9,r10
 	srdi	r10,r3,28 /* FIXME!! doing it twice */