Thread (47 messages) flat view 47 messages, 4 authors, 2012-07-24

Re: [PATCH -V3 11/11] arch/powerpc: Add 64TB support

From: Aneesh Kumar K.V <hidden>
Date: 2012-07-24 09:15:11
Subsystem: linux for powerpc (32-bit and 64-bit), the rest · Maintainers: Madhavan Srinivasan, Linus Torvalds 

"Aneesh Kumar K.V" [off-list ref] writes:

Paul Mackerras [off-list ref] writes:
quoted
On Mon, Jul 23, 2012 at 03:52:05PM +0530, Aneesh Kumar K.V wrote:
quoted
Paul Mackerras [off-list ref] writes:
quoted
On Mon, Jul 09, 2012 at 06:43:41PM +0530, Aneesh Kumar K.V wrote:
quoted
-#define USER_ESID_BITS		16
-#define USER_ESID_BITS_1T	4
+#define USER_ESID_BITS		18
+#define USER_ESID_BITS_1T	6
You also need to change the proto-VSID generation for kernel addresses
when you do this.  If you don't you'll end up with some user processes
using the same VSIDs as we use for the kernel addresses, meaning that
those processes won't run very well...
Can you explain this more. right now we generate vsid as below

vsid_scramble(ea >> SID_SHIFT, 256M) for kernel

vsid_scramble((context << USER_ESID_BITS) | (ea >> SID_SHIFT), 256M);
for user

what changes are you suggesting ?
Think about it.  With the current values of USER_ESID_BITS and
CONTEXT_BITS, and the addresses we use for kernel mappings, there are
no values of context, user_ea and kernel_ea for which

kernel_ea >> SID_SHIFT == (context << USER_ESID_BITS) | (user_ea >> SID_SHIFT)

If you increase USER_ESID_BITS, then there will be some context values
for which that equation becomes true.  For example, if you increase
USER_ESID_BITS to 18, then context 0x30000 will generate the same
proto-VSIDs as the kernel linear mapping.  Since we can hand out
contexts up to 0x7ffff (with CONTEXT_BITS = 19), there is a collision.

In other words, the proto-VSID space (the space of values that are
input to vsid_scramble) is currently divided into two mutually
exclusive regions: from 0 to 2^35 - 1 for user processes, and from
2^35 to 2^36 - 1 for kernel addresses.  You are wanting to expand the
amount of proto-VSID space that user processes can use, but you need
either to move the kernel portion of the space, or to make sure that
the context allocator doesn't hand out context values that would
collide with the kernel portion of the space (or both).
How about this ?. There is a FIXME in there which is not related.
Updated one with both the fixes. Let me know what you think

From f04a505be381b9c162fa41bda5df4a1a9edfdeb9 Mon Sep 17 00:00:00 2001
From: "Aneesh Kumar K.V" <redacted>
Date: Tue, 24 Jul 2012 14:22:15 +0530
Subject: [PATCH 1/2] arch/powerpc: properly offset the context bits for 1T
 segemnts

We should do rldimi r10,r9,USER_ESID_BITS,0 only after populating
r10 with ESID bits.

Signed-off-by: Aneesh Kumar K.V <redacted>
---
 arch/powerpc/mm/slb_low.S |   12 ++++++++----
 1 file changed, 8 insertions(+), 4 deletions(-)

diff --git a/arch/powerpc/mm/slb_low.S b/arch/powerpc/mm/slb_low.S
index db2cb3f..7bd8438 100644
--- a/arch/powerpc/mm/slb_low.S
+++ b/arch/powerpc/mm/slb_low.S
@@ -59,6 +59,7 @@ _GLOBAL(slb_miss_kernel_load_linear)
 BEGIN_FTR_SECTION
 	b	slb_finish_load
 END_MMU_FTR_SECTION_IFCLR(MMU_FTR_1T_SEGMENT)
+	srdi	r10,r10,40-28		/* get 1T ESID */
 	b	slb_finish_load_1T
 
 1:
@@ -88,6 +89,7 @@ _GLOBAL(slb_miss_kernel_load_vmemmap)
 BEGIN_FTR_SECTION
 	b	slb_finish_load
 END_MMU_FTR_SECTION_IFCLR(MMU_FTR_1T_SEGMENT)
+	srdi	r10,r10,40-28		/* get 1T ESID */
 	b	slb_finish_load_1T
 
 0:	/* user address: proto-VSID = context << 15 | ESID. First check
@@ -155,13 +157,16 @@ END_MMU_FTR_SECTION_IFCLR(MMU_FTR_1T_SEGMENT)
 	ld	r9,PACACONTEXTID(r13)
 BEGIN_FTR_SECTION
 	cmpldi	r10,0x1000
+	bge	9f
 END_MMU_FTR_SECTION_IFSET(MMU_FTR_1T_SEGMENT)
 	rldimi	r10,r9,USER_ESID_BITS,0
+	b	slb_finish_load
 BEGIN_FTR_SECTION
-	bge	slb_finish_load_1T
+9:
+	srdi	r10,r10,40-28		/* get 1T ESID */
+	rldimi	r10,r9,USER_ESID_BITS,0
+	b	slb_finish_load_1T
 END_MMU_FTR_SECTION_IFSET(MMU_FTR_1T_SEGMENT)
-	b	slb_finish_load
-
 8:	/* invalid EA */
 	li	r10,0			/* BAD_VSID */
 	li	r11,SLB_VSID_USER	/* flags don't much matter */
@@ -292,7 +297,6 @@ _GLOBAL(slb_compare_rr_to_size)
  * r3 = EA, r10 = proto-VSID, r11 = flags, clobbers r9
  */
 slb_finish_load_1T:
-	srdi	r10,r10,40-28		/* get 1T ESID */
 	ASM_VSID_SCRAMBLE(r10,r9,1T)
 	/*
 	 * bits above VSID_BITS_1T need to be ignored from r10
-- 
1.7.10


>From 43792d9e2c394370c71623f2769d11ff98090918 Mon Sep 17 00:00:00 2001
From: "Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com>
Date: Tue, 24 Jul 2012 11:40:29 +0530
Subject: [PATCH 2/2] arch/powerpc: properly isolate kernel and user
 proto-VSID

The proto-VSID space is divided into two class
User: 0 to 2^(CONTEXT_BITS + USER_ESID_BITS) -1
kernel: 2^(CONTEXT_BITS + USER_ESID_BITS) to 2^(VSID_BITS) - 1

This patch does above isolation

Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
---
 arch/powerpc/include/asm/mmu-hash64.h |   32 ++++++++++++++++++++++++--------
 arch/powerpc/kernel/exceptions-64s.S  |    4 +++-
 arch/powerpc/mm/slb_low.S             |   10 ++++++++++
 3 files changed, 37 insertions(+), 9 deletions(-)

diff --git a/arch/powerpc/include/asm/mmu-hash64.h b/arch/powerpc/include/asm/mmu-hash64.h
index daa3e4b..736df15 100644
--- a/arch/powerpc/include/asm/mmu-hash64.h
+++ b/arch/powerpc/include/asm/mmu-hash64.h
@@ -516,9 +516,19 @@ typedef struct {
 /* This is only valid for addresses >= PAGE_OFFSET */
 static inline unsigned long get_kernel_vsid(unsigned long ea, int ssize)
 {
-	if (ssize == MMU_SEGSIZE_256M)
-		return vsid_scramble(ea >> SID_SHIFT, 256M);
-	return vsid_scramble(ea >> SID_SHIFT_1T, 1T);
+	unsigned long proto_vsid;
+	/*
+	 * We need to make sure proto_vsid for the kernel is
+	 * >= 2^(CONTEXT_BITS + USER_ESID_BITS[_1T])
+	 */
+	if (ssize == MMU_SEGSIZE_256M) {
+		proto_vsid = ea >> SID_SHIFT;
+		proto_vsid |= (1UL << (CONTEXT_BITS + USER_ESID_BITS));
+		return vsid_scramble(proto_vsid, 256M);
+	}
+	proto_vsid = ea >> SID_SHIFT_1T;
+	proto_vsid |= (1UL << (CONTEXT_BITS + USER_ESID_BITS_1T));
+	return vsid_scramble(proto_vsid, 1T);
 }
 
 /* Returns the segment size indicator for a user address */
@@ -534,11 +544,17 @@ static inline int user_segment_size(unsigned long addr)
 static inline unsigned long get_vsid(unsigned long context, unsigned long ea,
 				     int ssize)
 {
-	if (ssize == MMU_SEGSIZE_256M)
-		return vsid_scramble((context << USER_ESID_BITS)
-				     | (ea >> SID_SHIFT), 256M);
-	return vsid_scramble((context << USER_ESID_BITS_1T)
-			     | (ea >> SID_SHIFT_1T), 1T);
+	unsigned long proto_vsid;
+	if (ssize == MMU_SEGSIZE_256M) {
+		proto_vsid = ((context << USER_ESID_BITS) |(ea >> SID_SHIFT));
+		/* truncate this to 37 bits */
+		proto_vsid &= (1UL << (CONTEXT_BITS + USER_ESID_BITS)) - 1;
+		return vsid_scramble(proto_vsid, 256M);
+	}
+	proto_vsid = ((context << USER_ESID_BITS_1T) | (ea >> SID_SHIFT_1T));
+	/* truncate this to 25 bits */
+	proto_vsid &= (1UL << (CONTEXT_BITS + USER_ESID_BITS_1T)) - 1;
+	return vsid_scramble( proto_vsid, 1T);
 }
 
 #endif /* __ASSEMBLY__ */
diff --git a/arch/powerpc/kernel/exceptions-64s.S b/arch/powerpc/kernel/exceptions-64s.S
index 1c06d29..40ed208 100644
--- a/arch/powerpc/kernel/exceptions-64s.S
+++ b/arch/powerpc/kernel/exceptions-64s.S
@@ -958,7 +958,9 @@ _GLOBAL(do_stab_bolted)
 	rldimi	r10,r11,7,52	/* r10 = first ste of the group */
 
 	/* Calculate VSID */
-	/* This is a kernel address, so protovsid = ESID */
+	/* This is a kernel address, so protovsid = ESID | 1 << 37 */
+	li	r9,0x1
+	rldimi  r11,r9,(CONTEXT_BITS + USER_ESID_BITS),0
 	ASM_VSID_SCRAMBLE(r11, r9, 256M)
 	rldic	r9,r11,12,16	/* r9 = vsid << 12 */
 
diff --git a/arch/powerpc/mm/slb_low.S b/arch/powerpc/mm/slb_low.S
index 7bd8438..e6bace3 100644
--- a/arch/powerpc/mm/slb_low.S
+++ b/arch/powerpc/mm/slb_low.S
@@ -57,9 +57,13 @@ _GLOBAL(slb_allocate_realmode)
 _GLOBAL(slb_miss_kernel_load_linear)
 	li	r11,0
 BEGIN_FTR_SECTION
+	li	r9,0x1
+	rldimi  r10,r9,(CONTEXT_BITS + USER_ESID_BITS),0
 	b	slb_finish_load
 END_MMU_FTR_SECTION_IFCLR(MMU_FTR_1T_SEGMENT)
 	srdi	r10,r10,40-28		/* get 1T ESID */
+	li	r9,0x1
+	rldimi  r10,r9,(CONTEXT_BITS + USER_ESID_BITS_1T),0
 	b	slb_finish_load_1T
 
 1:
@@ -87,9 +91,13 @@ _GLOBAL(slb_miss_kernel_load_vmemmap)
 	li	r11,0
 6:
 BEGIN_FTR_SECTION
+	li	r9,0x1
+	rldimi  r10,r9,(CONTEXT_BITS + USER_ESID_BITS),0
 	b	slb_finish_load
 END_MMU_FTR_SECTION_IFCLR(MMU_FTR_1T_SEGMENT)
 	srdi	r10,r10,40-28		/* get 1T ESID */
+	li	r9,0x1
+	rldimi  r10,r9,(CONTEXT_BITS + USER_ESID_BITS_1T),0
 	b	slb_finish_load_1T
 
 0:	/* user address: proto-VSID = context << 15 | ESID. First check
@@ -160,11 +168,13 @@ BEGIN_FTR_SECTION
 	bge	9f
 END_MMU_FTR_SECTION_IFSET(MMU_FTR_1T_SEGMENT)
 	rldimi	r10,r9,USER_ESID_BITS,0
+	clrldi	r10,r10,(64 - (CONTEXT_BITS + USER_ESID_BITS))
 	b	slb_finish_load
 BEGIN_FTR_SECTION
 9:
 	srdi	r10,r10,40-28		/* get 1T ESID */
 	rldimi	r10,r9,USER_ESID_BITS,0
+	clrldi	r10,r10,(64 - (CONTEXT_BITS + USER_ESID_BITS_1T))
 	b	slb_finish_load_1T
 END_MMU_FTR_SECTION_IFSET(MMU_FTR_1T_SEGMENT)
 8:	/* invalid EA */
-- 
1.7.10
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