Do a runtime CPUID update for a vCPU if MSR_IA32_XSS is written, as the
size in bytes of the XSAVE area is affected by the states enabled in XSS.

Fixes: 20300099 ("kvm: vmx: add MSR logic for XSAVES")
Cc: stable@vger.kernel.org
Signed-off-by: NLike Xu <likexu@tencent.com>
[sean: split out as a separate patch, adjust Fixes tag]
Signed-off-by: NSean Christopherson <seanjc@google.com>
Message-Id: <20220126172226.2298529-3-seanjc@google.com>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>