[Xen-changelog] [xen staging] x86emul: adjust MOVSXD source operand handling

[patchbot@xxxxxxx]

commit 89a854301e815a6f43a695605a5a261d964fcc6b
Author:     Jan Beulich <jbeulich@xxxxxxxx>
AuthorDate: Fri Oct 4 17:57:03 2019 +0200
Commit:     Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Fri Oct 4 17:57:03 2019 +0200

    x86emul: adjust MOVSXD source operand handling
    
    XED commit 1b2fd94425 ("Update MOVSXD to modern behavior") points out
    that as of SDM rev 064 MOVSXD is specified to read only 16 bits from
    memory (or register) when used without REX.W and with operand size
    override. Since the upper 16 bits of the value read won't be used
    anyway in this case, make the emulation uniformly follow this more
    compatible behavior when not emulating an AMD-like CPU, at the risk
    of missing an exception when emulating on/for older hardware (the
    boundary at SandyBridge noted in said commit looks questionable - I've
    observed the "new" behavior also on Westmere, and a discussion there
    lead to Mark finding that even Merom has this behavior already).
    
    Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
    Acked-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
    Release-acked-by: Juergen Gross <jgross@xxxxxxxx>
---
 xen/arch/x86/x86_emulate/x86_emulate.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/xen/arch/x86/x86_emulate/x86_emulate.c 
b/xen/arch/x86/x86_emulate/x86_emulate.c
index 22c29b8280..8f50a4f2de 100644
--- a/xen/arch/x86/x86_emulate/x86_emulate.c
+++ b/xen/arch/x86/x86_emulate/x86_emulate.c
@@ -4051,8 +4051,12 @@ x86_emulate(
             /* movsxd */
             if ( ea.type == OP_REG )
                 src.val = *ea.reg;
-            else if ( (rc = read_ulong(ea.mem.seg, ea.mem.off,
-                                       &src.val, 4, ctxt, ops)) )
+            else if ( (rc = read_ulong(ea.mem.seg, ea.mem.off, &src.val,
+                                       (op_bytes == 2 &&
+                                        !(ctxt->cpuid->x86_vendor &
+                                          (X86_VENDOR_AMD | X86_VENDOR_HYGON))
+                                        ? 2 : 4),
+                                       ctxt, ops)) )
                 goto done;
             dst.val = (int32_t)src.val;
         }
--
generated by git-patchbot for /home/xen/git/xen.git#staging

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