[PATCH] powerpc/64s: Remove EXSLB interrupt save area

[PATCH] powerpc/64s: Remove EXSLB interrupt save area

[Nicholas Piggin]

SLB faults should not be taken while the PACA save areas are live, all
memory accesses should be fetches from the kernel text, and access to
PACA and the current stack, before C code is called or any other
accesses are made.

All of these have pinned SLBs so will not take a SLB fault. Therefore
EXSLB is not be required.

Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
---
 arch/powerpc/include/asm/paca.h      | 3 +--
 arch/powerpc/kernel/asm-offsets.c    | 1 -
 arch/powerpc/kernel/exceptions-64s.S | 5 -----
 3 files changed, 1 insertion(+), 8 deletions(-)

diff --git a/arch/powerpc/include/asm/paca.h b/arch/powerpc/include/asm/paca.h
index 9454d29ff4b4..be0b00cb9fbb 100644
--- a/arch/powerpc/include/asm/paca.h
+++ b/arch/powerpc/include/asm/paca.h
@@ -108,8 +108,7 @@ struct paca_struct {
 	 */
 	/* used for most interrupts/exceptions */
 	u64 exgen[EX_SIZE] __attribute__((aligned(0x80)));
-	u64 exslb[EX_SIZE];	/* used for SLB/segment table misses
- 				 * on the linear mapping */
+
 	/* SLB related definitions */
 	u16 vmalloc_sllp;
 	u8 slb_cache_ptr;
diff --git a/arch/powerpc/kernel/asm-offsets.c b/arch/powerpc/kernel/asm-offsets.c
index b12d7c049bfe..31edd9bbce75 100644
--- a/arch/powerpc/kernel/asm-offsets.c
+++ b/arch/powerpc/kernel/asm-offsets.c
@@ -255,7 +255,6 @@ int main(void)
 #endif /* CONFIG_PPC_MM_SLICES */
 	OFFSET(PACA_EXGEN, paca_struct, exgen);
 	OFFSET(PACA_EXMC, paca_struct, exmc);
-	OFFSET(PACA_EXSLB, paca_struct, exslb);
 	OFFSET(PACA_EXNMI, paca_struct, exnmi);
 #ifdef CONFIG_PPC_PSERIES
 	OFFSET(PACALPPACAPTR, paca_struct, lppaca_ptr);
diff --git a/arch/powerpc/kernel/exceptions-64s.S b/arch/powerpc/kernel/exceptions-64s.S
index dad35b59bcfb..27fa80248406 100644
--- a/arch/powerpc/kernel/exceptions-64s.S
+++ b/arch/powerpc/kernel/exceptions-64s.S
@@ -1392,13 +1392,9 @@ ALT_MMU_FTR_SECTION_END_IFCLR(MMU_FTR_TYPE_RADIX)
  *   on user-handler data structures.
  *
  *   KVM: Same as 0x300, DSLB must test for KVM guest.
- *
- * A dedicated save area EXSLB is used (XXX: but it actually need not be
- * these days, we could use EXGEN).
  */
 INT_DEFINE_BEGIN(data_access_slb)
 	IVEC=0x380
-	IAREA=PACA_EXSLB
 	IDAR=1
 	IKVM_SKIP=1
 	IKVM_REAL=1
@@ -1481,7 +1477,6 @@ ALT_MMU_FTR_SECTION_END_IFCLR(MMU_FTR_TYPE_RADIX)
  */
 INT_DEFINE_BEGIN(instruction_access_slb)
 	IVEC=0x480
-	IAREA=PACA_EXSLB
 	IISIDE=1
 	IDAR=1
 #ifdef CONFIG_KVM_BOOK3S_PR_POSSIBLE
-- 
2.23.0

Re: [PATCH] powerpc/64s: Remove EXSLB interrupt save area

[Michael Ellerman]

On Mon, 8 Feb 2021 16:34:06 +1000, Nicholas Piggin wrote:
> SLB faults should not be taken while the PACA save areas are live, all
> memory accesses should be fetches from the kernel text, and access to
> PACA and the current stack, before C code is called or any other
> accesses are made.
> 
> All of these have pinned SLBs so will not take a SLB fault. Therefore
> EXSLB is not be required.

Applied to powerpc/next.

[1/1] powerpc/64s: Remove EXSLB interrupt save area
      https://git.kernel.org/powerpc/c/ac7c5e9b08acdb54ef3525abcad24bdb3ed05551

cheers