On Thu, Oct 02, 2025 at 04:02:00PM +0200, Alejandro Vallejo wrote: > On Thu Oct 2, 2025 at 3:38 PM CEST, Roger Pau Monné wrote: > > On Thu, Oct 02, 2025 at 11:37:36AM +0100, Andrew Cooper wrote: > >> 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? > > > > I came across the documentation above and I didn't remember Xen > > returning any value for reads, which sadly was indeed true. > > > > This was because I had the intention to suggest Alejandro to (also?) use > > the port 0xe9 hack for printing from XTF, which should work for both > > Xen and QEMU. > > QEMU doesn't support 0xE9 though?
AFAICT it does: https://wiki.osdev.org/QEMU#The_debug_console However when running QEMU on Xen as a device model writes to 0xe9 are handled in the hypervisor, and never forwarded to any device model. Regards, Roger.
