[PowerPC64LE] Work around qemu TCG bug in mtmsrd emulation.

The TCG implementation of mtmsrd in qemu blindly copies the entire register
to the MSR, instead of the specific bit positions listed in the ISA.

This means that qemu will prematurely switch endian out from under the
running code instead of waiting for the rfid, causing an immediate trap
as it attempts to interpret the next instruction in the wrong endianness.

To work around this, ensure PSL_LE is still set before doing the mtmsrd.

In the future, we may wish to just turn off translation and unconditionally
use rfid to switch to the ofmsr instead of quasi-switching to the ofmsr.

Add a new platform option so this can be disabled. (And so that we can
conditonalize additional QEMU-specific hacks in the platform code.)

Sponsored by:	Tag1 Consulting, Inc.

5 files changed, 24 insertions, 0 deletions

diff --git a/sys/conf/options.powerpc b/sys/conf/options.powerpc
index 6e9eb81ecaf0..1a22f931450a 100644
--- a/sys/conf/options.powerpc
+++ b/sys/conf/options.powerpc
@@ -29,6 +29,7 @@ MAMBO
 POWERNV			opt_platform.h
 PSERIES
 PSIM
+QEMU			opt_platform.h
 
 SC_OFWFB		opt_ofwfb.h
 
diff --git a/sys/powerpc/conf/GENERIC64 b/sys/powerpc/conf/GENERIC64
index a70cd0db605d..18eedb7f927a 100644
--- a/sys/powerpc/conf/GENERIC64
+++ b/sys/powerpc/conf/GENERIC64
@@ -30,6 +30,7 @@ makeoptions	WITH_CTF=1
 options 	POWERMAC		#NewWorld Apple PowerMacs
 options 	PS3			#Sony Playstation 3
 options 	MAMBO			#IBM Mambo Full System Simulator
+options		QEMU			#QEMU processor emulator
 options 	PSERIES			#PAPR-compliant systems (e.g. IBM p)
 options 	POWERNV			#Non-virtualized OpenPOWER systems
 
diff --git a/sys/powerpc/conf/NOTES b/sys/powerpc/conf/NOTES
index 74a03f2cedcd..c41a0a61184d 100644
--- a/sys/powerpc/conf/NOTES
+++ b/sys/powerpc/conf/NOTES
@@ -44,6 +44,7 @@ options 	POWERMAC		#NewWorld Apple PowerMacs
 #options	PS3			#Sony Playstation 3
 options 	PSIM			#GDB PSIM ppc simulator
 options 	MAMBO			#IBM Mambo Full System Simulator
+options		QEMU			#QEMU processor emulator
 
 # The cpufreq(4) driver provides support for CPU frequency control
 device		cpufreq
diff --git a/sys/powerpc/ofw/ofwcall64.S b/sys/powerpc/ofw/ofwcall64.S
index 481c109affd2..3230cdf79c37 100644
--- a/sys/powerpc/ofw/ofwcall64.S
+++ b/sys/powerpc/ofw/ofwcall64.S
@@ -32,6 +32,8 @@
 #include <machine/spr.h>
 #include <machine/asm.h>
 
+#include "opt_platform.h"
+
 #define	OFWSTKSZ	4096		/* 4K Open Firmware stack */
 
 /*
@@ -119,6 +121,10 @@ ASENTRY_NOPROF(ofwcall)
 	addis	%r5,%r2,TOC_REF(ofmsr)@ha
 	ld	%r5,TOC_REF(ofmsr)@l(%r5)
 	ld	%r5,0(%r5)
+#if defined(__LITTLE_ENDIAN__) && defined(QEMU)
+	/* QEMU hack: qemu does not emulate mtmsrd correctly! */
+	ori	%r5,%r5,1	/* Leave PSR_LE set */
+#endif
 	mtmsrd	%r5
 	isync
 
@@ -270,6 +276,10 @@ ASENTRY_NOPROF(rtascall)
 	addis	%r7,%r2,TOC_REF(rtasmsr)@ha
 	ld	%r7,TOC_REF(rtasmsr)@l(%r7)
 	ld	%r7,0(%r7)
+#ifdef	__LITTLE_ENDIAN__
+	/* QEMU hack: qemu does not emulate mtmsrd correctly! */
+	ori	%r7,%r7,1	/* Leave PSR_LE set */
+#endif
 	mtmsrd	%r7
 	isync
 
diff --git a/sys/powerpc/powernv/opalcall.S b/sys/powerpc/powernv/opalcall.S
index 1d1f60353ade..56ba5c7f1863 100644
--- a/sys/powerpc/powernv/opalcall.S
+++ b/sys/powerpc/powernv/opalcall.S
@@ -27,6 +27,8 @@
 
 #include <machine/asm.h>
 
+#include "opt_platform.h"
+
 GLOBAL(opal_entrypoint)
 	.llong	0
 GLOBAL(opal_data)
@@ -70,8 +72,17 @@ ASENTRY(opal_call)
 	ld	%r2,TOC_REF(opal_data)@l(%r2)
 	ld	%r2,0(%r2)
 
+
+#if defined(__LITTLE_ENDIAN__) && defined(QEMU)
+	/* QEMU hack: qemu does not emulate mtmsrd correctly! */
+	ori     %r3,%r3,1       /* Leave PSR_LE set */
+#endif
 	mtmsrd	%r3
 	isync
+#if defined(__LITTLE_ENDIAN__) && defined(QEMU)
+	/* Clean up from qemu hack */
+	xori	%r3,%r3,1
+#endif
 
 	/* Shift registers over */
 	mr	%r3,%r4