Reading from the E9 port if the emergency console is active should return 0xe9 according to the documentation from Bochs:
https://bochs.sourceforge.io/doc/docbook/user/bochsrc.html See `port_e9_hack` section description. Fix Xen so it also returns the port address. OSes can use it to detect whether the emergency console is available or not. Fixes: d1bd157fbc9b ("Big merge the HVM full-virtualisation abstractions.") Signed-off-by: Roger Pau Monné <[email protected]> --- xen/arch/x86/hvm/hvm.c | 12 +++++++++--- 1 file changed, 9 insertions(+), 3 deletions(-) diff --git a/xen/arch/x86/hvm/hvm.c b/xen/arch/x86/hvm/hvm.c index 23bd7f078a1d..0c60faa39d7b 100644 --- a/xen/arch/x86/hvm/hvm.c +++ b/xen/arch/x86/hvm/hvm.c @@ -567,9 +567,15 @@ static int cf_check hvm_print_line( ASSERT(bytes == 1 && port == XEN_HVM_DEBUGCONS_IOPORT); - /* Deny any input requests. */ - if ( dir != IOREQ_WRITE ) - return X86EMUL_UNHANDLEABLE; + if ( dir == IOREQ_READ ) + { + /* + * According to Bochs documentation, reading from the E9 port should + * return 0xE9 if the "port E9 hack" is implemented. + */ + *val = XEN_HVM_DEBUGCONS_IOPORT; + return X86EMUL_OKAY; + } if ( !is_console_printable(c) ) return X86EMUL_OKAY; -- 2.51.0
