On 02/10/2025 11:22 am, Roger Pau Monne wrote: > 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]>
Reviewed-by: Andrew Cooper <[email protected]> That's been wrong for rather a long time. How did you find it? CC-ing Oleksii as you've tagged this for 4.21. > --- > 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;
