[xen staging] libxenguest/x86: ensure CPUID[1].EBX[32:16] is non-zero for HVM

[patchbot@xxxxxxx]

commit daaf007eb3467f900a2e20fadbc4c6f3bfcaa356
Author:     Jan Beulich <jbeulich@xxxxxxxx>
AuthorDate: Mon Aug 30 15:19:31 2021 +0200
Commit:     Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Mon Aug 30 15:19:31 2021 +0200

    libxenguest/x86: ensure CPUID[1].EBX[32:16] is non-zero for HVM
    
    We unconditionally set HTT, so merely doubling the value read from
    hardware isn't going to be correct if that value is zero.
    
    Reported-by: Julien Grall <julien@xxxxxxx>
    Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
    Tested-by: Julien Grall <julien@xxxxxxx>
    Acked-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
---
 tools/libs/guest/xg_cpuid_x86.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/tools/libs/guest/xg_cpuid_x86.c b/tools/libs/guest/xg_cpuid_x86.c
index 0c9c4fefc1..198892ebdf 100644
--- a/tools/libs/guest/xg_cpuid_x86.c
+++ b/tools/libs/guest/xg_cpuid_x86.c
@@ -594,7 +594,9 @@ int xc_cpuid_apply_policy(xc_interface *xch, uint32_t 
domid, bool restore,
          * Update to reflect vLAPIC_ID = vCPU_ID * 2, but make sure to avoid
          * overflow.
          */
-        if ( !(p->basic.lppp & 0x80) )
+        if ( !p->basic.lppp )
+            p->basic.lppp = 2;
+        else if ( !(p->basic.lppp & 0x80) )
             p->basic.lppp *= 2;
 
         switch ( p->x86_vendor )
--
generated by git-patchbot for /home/xen/git/xen.git#staging