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

[Yuchen <yu.chen@h3c.com>]

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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.chen@h3c.com>
---
target/i386/xsave_helper.c | 8 ++++++++
1 file changed, 8 insertions(+)

diff --git a/target/i386/xsave_helper.c b/target/i386/xsave_helper.c
index 996e9f3bfe..64e2b969fe 100644
--- a/target/i386/xsave_helper.c
+++ b/target/i386/xsave_helper.c
@@ -6,6 +6,8 @@
 #include "cpu.h"
+static bool has_xsave_pkru;
+
void x86_cpu_xsave_all_areas(X86CPU *cpu, void *buf, uint32_t buflen)
{
     CPUX86State *env = &cpu->env;
@@ -47,6 +49,9 @@ void x86_cpu_xsave_all_areas(X86CPU *cpu, void *buf, uint32_t buflen)
         stq_p(xmm + 8, env->xmm_regs[i].ZMM_Q(1));
     }
+    if (!has_xsave_pkru) {
+        env->xstate_bv &= ~XSTATE_PKRU_MASK;
+    }
     header->xstate_bv = env->xstate_bv;
     e = &x86_ext_save_areas[XSTATE_YMM_BIT];
@@ -181,6 +186,9 @@ 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);
     }
+    if (xsave->header.xstate_bv & XSTATE_PKRU_MASK) {
+        has_xsave_pkru = true;
+    }
     env->xstate_bv = header->xstate_bv;
     e = &x86_ext_save_areas[XSTATE_YMM_BIT];
--
2.34.1
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