[PATCH v5 1/5] KVM: PPC: e500mc: Revert "add load inst fixup"

Mihai Caraman mihai.caraman at freescale.com
Thu Jul 17 21:22:24 EST 2014

The commit 1d628af7 "add load inst fixup" made an attempt to handle
failures generated by reading the guest current instruction. The fixup
code that was added works by chance hiding the real issue.

Load external pid (lwepx) instruction, used by KVM to read guest
instructions, is executed in a subsituted guest translation context
(EPLC[EGS] = 1). In consequence lwepx's TLB error and data storage
interrupts need to be handled by KVM, even though these interrupts
are generated from host context (MSR[GS] = 0) where lwepx is executed.

Currently, KVM hooks only interrupts generated from guest context
(MSR[GS] = 1), doing minimal checks on the fast path to avoid host
performance degradation. As a result, the host kernel handles lwepx
faults searching the faulting guest data address (loaded in DEAR) in
its own Logical Partition ID (LPID) 0 context. In case a host translation
is found the execution returns to the lwepx instruction instead of the
fixup, the host ending up in an infinite loop.

Revert the commit "add load inst fixup". lwepx issue will be addressed
in a subsequent patch without needing fixup code.

Signed-off-by: Mihai Caraman <mihai.caraman at freescale.com>
 - no change

 arch/powerpc/kvm/bookehv_interrupts.S | 26 +-------------------------
 1 file changed, 1 insertion(+), 25 deletions(-)

diff --git a/arch/powerpc/kvm/bookehv_interrupts.S b/arch/powerpc/kvm/bookehv_interrupts.S
index a1712b8..6ff4480 100644
--- a/arch/powerpc/kvm/bookehv_interrupts.S
+++ b/arch/powerpc/kvm/bookehv_interrupts.S
@@ -29,7 +29,6 @@
 #include <asm/asm-compat.h>
 #include <asm/asm-offsets.h>
 #include <asm/bitsperlong.h>
-#include <asm/thread_info.h>
 #ifdef CONFIG_64BIT
 #include <asm/exception-64e.h>
@@ -164,32 +163,9 @@
 	PPC_STL	r30, VCPU_GPR(R30)(r4)
 	PPC_STL	r31, VCPU_GPR(R31)(r4)
 	mtspr	SPRN_EPLC, r8
-	/* disable preemption, so we are sure we hit the fixup handler */
-	li	r7, 1
-	stw	r7, TI_PREEMPT(r8)
-	/*
-	 * In case the read goes wrong, we catch it and write an invalid value
-	 * in LAST_INST instead.
-	 */
-1:	lwepx	r9, 0, r5
-.section .fixup, "ax"
-	b	2b
-.section __ex_table,"a"
-	PPC_LONG 1b,3b
+	lwepx   r9, 0, r5
 	mtspr	SPRN_EPLC, r3
-	li	r7, 0
-	stw	r7, TI_PREEMPT(r8)
 	stw	r9, VCPU_LAST_INST(r4)

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