libxc/x86: Report consistent initial APIC value for PV guests

Currently hypervisor provides PV guest's CPUID(1).EBX[31:24] (initial
APIC ID) with contents of that field on the processor that launched
the guest. This results in the guest reporting different initial
APIC IDs across runs.

We should be consistent in how this value is reported, let's set
it to 0 (which is also what Linux guests expect).

Signed-off-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>
Acked-by: Wei Liu <wei.liu2@citrix.com>
[ wei: remove trailing whitespace in comment ]
Signed-off-by: Wei Liu <wei.liu2@citrix.com>
Release-acked-by: Wei Liu <wei.liu2@citrix.com>

diff --git a/tools/libxc/xc_cpuid_x86.c b/tools/libxc/xc_cpuid_x86.c
index d761805da06a147f85987d5c7eebbf60ce1ea855..2ad9aebfce66689369215174c1579264c951132e 100644 (file)
--- a/tools/libxc/xc_cpuid_x86.c
+++ b/tools/libxc/xc_cpuid_x86.c
@@ -618,6 +618,12 @@ static void xc_cpuid_pv_policy(xc_interface *xch,
         /* Host topology exposed to PV guest.  Provide host value. */
         bool host_htt = regs[3] & bitmaskof(X86_FEATURE_HTT);
 
+        /*
+         * Don't pick host's Initial APIC ID which can change from run
+         * to run.
+         */
+        regs[1] &= 0x00ffffffu;
+
         regs[2] = info->featureset[featureword_of(X86_FEATURE_SSE3)];
         regs[3] = (info->featureset[featureword_of(X86_FEATURE_FPU)] &
                    ~bitmaskof(X86_FEATURE_HTT));