[PATCH v1 1/1] target/i386: Mask xstate_bv based on the cpu enabled features

[Leonardo Bras]

The following steps describe a migration bug:
1 - Bring up a VM with -cpu EPYC on a host with EPYC-Milan cpu
2 - Migrate to a host with EPYC-Naples cpu

The guest kernel crashes shortly after the migration.

The crash happens due to a fault caused by XRSTOR:
A set bit in XSTATE_BV is not set in XCR0.
The faulting bit is FEATURE_PKRU (enabled in Milan, but not in Naples)

To avoid this kind of bug:
In kvm_get_xsave, mask-out from xstate_bv any bits that are not set in
current vcpu's features.

This keeps cpu->env->xstate_bv with feature bits compatible with any
host machine capable of running the vcpu model.

Signed-off-by: Leonardo Bras <leobras@redhat.com>
---
 target/i386/xsave_helper.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/target/i386/xsave_helper.c b/target/i386/xsave_helper.c
index ac61a96344..0628226234 100644
--- a/target/i386/xsave_helper.c
+++ b/target/i386/xsave_helper.c
@@ -167,7 +167,7 @@ void x86_cpu_xrstor_all_areas(X86CPU *cpu, const void *buf, 
uint32_t buflen)
         env->xmm_regs[i].ZMM_Q(1) = ldq_p(xmm + 8);
     }
 
-    env->xstate_bv = header->xstate_bv;
+    env->xstate_bv = header->xstate_bv & env->features[FEAT_XSAVE_COMP_LO];
 
     e = &x86_ext_save_areas[XSTATE_YMM_BIT];
     if (e->size && e->offset) {
-- 
2.34.1