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To: "xen-devel@lists.xenproject.org" <xen-devel@lists.xenproject.org>
From: Jan Beulich <jbeulich@suse.com>
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Date: Thu, 14 Nov 2019 11:13:14 +0100
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Subject: [Xen-devel] [PATCH] x86emul: 16-bit XBEGIN does not truncate rIP
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Cc: Juergen Gross <jgross@suse.com>,
 Andrew Cooper <andrew.cooper3@citrix.com>, Wei Liu <wl@xen.org>,
	=?utf-8?q?Roger_Pau_Monn=C3=A9?= <roger.pau@citrix.com>
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SDM rev 071 points out this fact explicitly.

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
@@ -4246,10 +4246,12 @@ x86_emulate(
         {
             /*
              * xbegin unconditionally aborts, xabort is unconditionally
-             * a nop.
+             * a nop. It also does not truncate the destination address to
+             * 16 bits when 16-bit operand size is in effect.
              */
             if ( b & 1 )
             {
+                op_bytes = 4;
                 jmp_rel((int32_t)src.val);
                 _regs.r(ax) = 0;
             }