From 67f85346ca9305d9fb3254ceff735ceaadeb0911 Mon Sep 17 00:00:00 2001 From: Nicholas Piggin Date: Tue, 27 Jun 2023 16:14:06 +1000 Subject: [PATCH] icount: don't adjust virtual time backwards after warp The icount-based QEMU_CLOCK_VIRTUAL runs ahead of the RT clock at times. When warping, it is possible it is still ahead at the end of the warp, which causes icount adaptive mode to adjust it backward. This can result in the machine observing time going backwards. Prevent this by clamping adaptive adjustment to 0 at minimum. Signed-off-by: Nicholas Piggin Message-ID: <20230627061406.241847-1-npiggin@gmail.com> Cc: qemu-stable@nongnu.org Signed-off-by: Paolo Bonzini --- softmmu/icount.c | 9 +++++++-- 1 file changed, 7 insertions(+), 2 deletions(-) diff --git a/softmmu/icount.c b/softmmu/icount.c index 4504433e16..a5cef9c60a 100644 --- a/softmmu/icount.c +++ b/softmmu/icount.c @@ -259,11 +259,16 @@ static void icount_warp_rt(void) warp_delta = clock - timers_state.vm_clock_warp_start; if (icount_enabled() == 2) { /* - * In adaptive mode, do not let QEMU_CLOCK_VIRTUAL run too - * far ahead of real time. + * In adaptive mode, do not let QEMU_CLOCK_VIRTUAL run too far + * ahead of real time (it might already be ahead so careful not + * to go backwards). */ int64_t cur_icount = icount_get_locked(); int64_t delta = clock - cur_icount; + + if (delta < 0) { + delta = 0; + } warp_delta = MIN(warp_delta, delta); } qatomic_set_i64(&timers_state.qemu_icount_bias,