Re: [PATCH] target/i386: Clear xsave pkru bit when KVM XCR0 not support

[Paolo Bonzini]

On 5/17/23 12:55, Yuchen wrote:
Migrating guest from Intel new CPU (as Gold 6230) to old CPU (as
E5-2650 v4) will pause on the destination host. Because old CPU
not support xsave pkru feature, and KVM KVM_SET_XSAVE ioctl
return EINVAL.
This kernel commit introduces the problem:

ea4d6938d4c0 x86/fpu: Replace KVMs home brewed FPU copy from user

Signed-off-by: YuChen <yu.c...@h3c.com>

Would this work instead?

diff --git a/target/i386/xsave_helper.c b/target/i386/xsave_helper.c
index 996e9f3bfef5..d3e5edad2ecd 100644
--- a/target/i386/xsave_helper.c
+++ b/target/i386/xsave_helper.c
@@ -47,7 +47,7 @@ void x86_cpu_xsave_all_areas(X86CPU *cpu, void *buf, uint32_t 
buflen)
         stq_p(xmm + 8, env->xmm_regs[i].ZMM_Q(1));
     }
 
-    header->xstate_bv = env->xstate_bv;
+    header->xstate_bv = env->xstate_bv & x86_cpu_xsave_xcr0_components(cpu);
 
     e = &x86_ext_save_areas[XSTATE_YMM_BIT];
     if (e->size && e->offset) {

Paolo