From db5a3c31a650d3fb0945f77f8ceda133412b5ce0 Mon Sep 17 00:00:00 2001 From: Roger Pau Monne Date: Thu, 2 Oct 2025 11:44:09 +0200 Subject: [PATCH] x86/hvm: fix reading from 0xe9 IO port if port E9 hack is active MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit 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 Reviewed-by: Andrew Cooper --- 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 23bd7f078a..0c60faa39d 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;