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[Qemu-devel] [PULL 1/3] ppc: fix setting of compat mode

From: David Gibson
Subject: [Qemu-devel] [PULL 1/3] ppc: fix setting of compat mode
Date: Wed, 8 Nov 2017 19:12:30 +1100

From: Greg Kurz <address@hidden>

While trying to make KVM PR usable again, commit 5dfaa532ae introduced a
regression: the current compat_pvr value is passed to KVM instead of the
new one. This means that we always pass 0 instead of the max-cpu-compat
PVR during the initial machine reset. And at CAS time, we either pass
the PVR from the command line or even don't call kvmppc_set_compat() at
all, ie, the PCR will not be set as expected.

For example if we start a big endian fedora26 guest in power7 compat
mode on a POWER8 host, we get this in the guest:

$ cat /proc/cpuinfo
processor       : 0
cpu             : POWER7 (architected), altivec supported
clock           : 4024.000000MHz
revision        : 2.0 (pvr 004d 0200)

timebase        : 512000000
platform        : pSeries
model           : IBM pSeries (emulated by qemu)
machine         : CHRP IBM pSeries (emulated by qemu)
MMU             : Hash

but the guest can still execute POWER8 instructions, and the following
program succeeds:

int main()
        asm("vncipher 0,0,0"); // ISA 2.07 instruction

Let's pass the new compat_pvr to kvmppc_set_compat() and the program fails
with SIGILL as expected.

Reported-by: Nageswara R Sastry <address@hidden>
Signed-off-by: Greg Kurz <address@hidden>
Signed-off-by: David Gibson <address@hidden>
 target/ppc/compat.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/target/ppc/compat.c b/target/ppc/compat.c
index f8729fe46d..ad8f93c064 100644
--- a/target/ppc/compat.c
+++ b/target/ppc/compat.c
@@ -141,7 +141,7 @@ void ppc_set_compat(PowerPCCPU *cpu, uint32_t compat_pvr, 
Error **errp)
     if (kvm_enabled() && cpu->compat_pvr != compat_pvr) {
-        int ret = kvmppc_set_compat(cpu, cpu->compat_pvr);
+        int ret = kvmppc_set_compat(cpu, compat_pvr);
         if (ret < 0) {
             error_setg_errno(errp, -ret,
                              "Unable to set CPU compatibility mode in KVM");

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