cpu/i386: update xsave components after CPUID filtering

[Huanyu Zhai]

From: NikoZHAI <huanyu.zhai@outlook.com>

On i386 platform, CPUID data are setup through three consecutive steps: CPU 
model definition, expansion and filtering.
XSAVE components are enabled during the expansion stage, by checking if they 
are enabled in CPUID. However, it is still
probable that some XSAVE features will be enabled/disabled during the filtering 
stage and the XSAVE components left unchanged.
Inconsistency between XSAVE features and enabled XSAVE components can lead to 
problems on some Linux guests in the absence of
the following patch in the kernel:

https://www.mail-archive.com/linux-kernel@vger.kernel.org/msg1452368.html

A simple case to reproduce this problem is to start a SUSE 12 SP3 guest with 
cpu model set to Skylake-Server:
$ qemu-system-x86_64 -cpu Skylake-Server ...

In the SUSE 12 SP3 guest, one can observe that PKRU will be enabled without 
Intel PKU's presence.
That's because on platform with Skylake-Server cpus, Intel PKU is disabled 
during x86_cpu_filter_features(),
but the XSAVE PKRU bit was enabled by x86_cpu_expand_features().

Signed-off-by: Huanyu Zhai <huanyu.zhai@outlook.com>
Co-authored-by: Wang Xin <wangxinxin.wang@huawei.com>
---
 target/i386/cpu.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/target/i386/cpu.c b/target/i386/cpu.c
index 1242bd541a..1f6424bd80 100644
--- a/target/i386/cpu.c
+++ b/target/i386/cpu.c
@@ -6901,6 +6901,9 @@ static void x86_cpu_filter_features(X86CPU *cpu, bool 
verbose)
             mark_unavailable_features(cpu, FEAT_7_0_EBX, 
CPUID_7_0_EBX_INTEL_PT, prefix);
         }
     }
+
+    /* Update XSAVE components again based on the filtered CPU feature flags */
+    x86_cpu_enable_xsave_components(cpu);
 }
 
 static void x86_cpu_hyperv_realize(X86CPU *cpu)
-- 
2.39.3