File 634561f1-x86emul-respect-NSCB.patch of Package xen.26660

# Commit 87a20c98d9f0f422727fe9b4b9e22c2c43a5cd9c
# Date 2022-10-11 14:30:41 +0200
# Author Jan Beulich <jbeulich@suse.com>
# Committer Jan Beulich <jbeulich@suse.com>
x86emul: respect NSCB

protmode_load_seg() would better adhere to that "feature" of clearing
base (and limit) during NULL selector loads.

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>

--- a/xen/arch/x86/x86_emulate/x86_emulate.c
+++ b/xen/arch/x86/x86_emulate/x86_emulate.c
@@ -1970,6 +1970,7 @@ amd_like(const struct x86_emulate_ctxt *
 #define vcpu_has_tbm()         (ctxt->cpuid->extd.tbm)
 #define vcpu_has_clzero()      (ctxt->cpuid->extd.clzero)
 #define vcpu_has_wbnoinvd()    (ctxt->cpuid->extd.wbnoinvd)
+#define vcpu_has_nscb()        (ctxt->cpuid->extd.nscb)
 
 #define vcpu_has_bmi1()        (ctxt->cpuid->feat.bmi1)
 #define vcpu_has_hle()         (ctxt->cpuid->feat.hle)
@@ -2102,7 +2103,7 @@ protmode_load_seg(
         case x86_seg_tr:
             goto raise_exn;
         }
-        if ( !_amd_like(cp) || !ops->read_segment ||
+        if ( !_amd_like(cp) || vcpu_has_nscb() || !ops->read_segment ||
              ops->read_segment(seg, sreg, ctxt) != X86EMUL_OKAY )
             memset(sreg, 0, sizeof(*sreg));
         else