[PATCH v2] target-i386: fix losing XCR0 processor state component bits

[Wanpeng Li <kernellwp@gmail.com>]

From: Wanpeng Li <wanpeng.li@hotmail.com>

Commit 96193c22a "target-i386: Move xsave component mask to features array"
leverages features array to handle XCR0 processor state component bits, 
however, it introduces a regression:

warning: host doesn't support requested feature: CPUID.0DH:EAX [bit 0]
warning: host doesn't support requested feature: CPUID.0DH:EAX [bit 1]
warning: host doesn't support requested feature: CPUID.0DH:EAX [bit 2]

My desktop doesn't have enough advance features, so just X87,SSE,AVX 
warnings are splat when I boot a guest.

The get migratable flags logic in x86_cpu_filter_features() path will 
filter out the feature flags which are unsupported and unmigratable. 
However, the bits of XCR0 processor state component featureword don't 
have feat_names, and some features like SSE/AVX etc have feat_names in 
CPUID.01H:EDX, CPUID.01H:ECX, so they are treated as unsupported.

This patch fix it by don't filter out XCR0 processor state components 
bits though they don't have feat_names just as before commit 96193c22ab3.

Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Richard Henderson <rth@twiddle.net>
Cc: Eduardo Habkost <ehabkost@redhat.com>
Cc: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Wanpeng Li <wanpeng.li@hotmail.com>
---
v1 -> v2: 
 * move the check to x86_cpu_get_migratable_flags()

 target-i386/cpu.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/target-i386/cpu.c b/target-i386/cpu.c
index 333309b..cc929ca 100644
--- a/target-i386/cpu.c
+++ b/target-i386/cpu.c
@@ -602,7 +602,10 @@ static uint32_t x86_cpu_get_migratable_flags(FeatureWord w)
         uint32_t f = 1U << i;
         /* If the feature name is unknown, it is not supported by QEMU yet */
         if (!wi->feat_names[i]) {
-            continue;
+            if (w != FEAT_XSAVE_COMP_LO &&
+                w != FEAT_XSAVE_COMP_HI) {
+                continue;
+            }
         }
         /* Skip features known to QEMU, but explicitly marked as unmigratable */
         if (wi->unmigratable_flags & f) {
-- 
1.9.1