[Xen-devel] [PATCH] x86: don't clear high 32 bits of RAX on sub-word guest I/O port reads

["Jan Beulich" <JBeulich@xxxxxxxx>]

1- or 2-byte operations never alter the high halves of registers.

Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>

--- a/xen/arch/x86/traps.c
+++ b/xen/arch/x86/traps.c
@@ -2234,7 +2234,7 @@ static int emulate_privileged_op(struct 
             if ( op_bytes == 4 )
                 regs->eax = 0;
             else
-                regs->eax &= ~((1u << (op_bytes * 8)) - 1);
+                regs->eax &= ~((1 << (op_bytes * 8)) - 1);
             regs->eax |= guest_io_read(port, op_bytes, v, regs);
         }
         bpmatch = check_guest_io_breakpoint(v, port, op_bytes);

Attachment: x86-PV-IO-read-high-bits.patch
Description: Text document

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