Commit 8bb93c6f authored by Alex Bennée's avatar Alex Bennée Committed by Gerd Hoffmann
Browse files

ui/console: ensure graphic updates don't race with TCG vCPUs 



Commit 8d04fb55..

  tcg: drop global lock during TCG code execution

..broke the assumption that updates to the GUI couldn't happen at the
same time as TCG vCPUs where running. As a result the TCG vCPU could
still be updating a directly mapped frame-buffer while the display
side was updating. This would cause artefacts to appear when the
update code assumed that memory block hadn't changed.

The simplest solution is to ensure the two things can't happen at the
same time like the old BQL locking scheme. Here we use the solution
introduced for MTTCG and schedule the update as async_safe_work when
we know no vCPUs can be running.

Reported-by: default avatarMark Cave-Ayland <mark.cave-ayland@ilande.co.uk>
Signed-off-by: default avatarAlex Bennée <alex.bennee@linaro.org>
Message-id: 20170315144825.3108-1-alex.bennee@linaro.org
Cc: BALATON Zoltan <balaton@eik.bme.hu>
Cc: Gerd Hoffmann <kraxel@redhat.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: default avatarAlex Bennée <alex.bennee@linaro.org>

[ kraxel: updated comment clarifying the display adapters are buggy
          and this is a temporary workaround ]

Signed-off-by: default avatarGerd Hoffmann <kraxel@redhat.com>
parent 272d7dee

ui/console.c

+20 −1
Original line number Diff line number Diff line
@@ -1575,16 +1575,35 @@ bool dpy_gfx_check_format(QemuConsole *con, 
    return true;

}



/*

 * Safe DPY refresh for TCG guests. This runs when the TCG vCPUs are

 * quiescent so we can avoid races between dirty page tracking for

 * direct frame-buffer access by the guest.

 *

 * This is a temporary stopgap until we've fixed the dirty tracking

 * races in display adapters.

 */

static void do_safe_dpy_refresh(CPUState *cpu, run_on_cpu_data opaque)

{

    DisplayChangeListener *dcl = opaque.host_ptr;

    dcl->ops->dpy_refresh(dcl);

}



static void dpy_refresh(DisplayState *s)

{

    DisplayChangeListener *dcl;



    QLIST_FOREACH(dcl, &s->listeners, next) {

        if (dcl->ops->dpy_refresh) {

            if (tcg_enabled()) {

                async_safe_run_on_cpu(first_cpu, do_safe_dpy_refresh,

                                      RUN_ON_CPU_HOST_PTR(dcl));

            } else {

                dcl->ops->dpy_refresh(dcl);

            }

        }

    }

}



void dpy_text_cursor(QemuConsole *con, int x, int y)

{