On 7/17/20 5:49 PM, Jessica Clarke wrote: > The specification says: > > 0x00 TIME_LOW R: Get current time, then return low-order 32-bits. > 0x04 TIME_HIGH R: Return high 32-bits from previous TIME_LOW read. > > ... > > To read the value, the kernel must perform an IO_READ(TIME_LOW), > which returns an unsigned 32-bit value, before an IO_READ(TIME_HIGH), > which returns a signed 32-bit value, corresponding to the higher half > of the full value. > > However, we were just returning the current time for both. If the guest > is unlucky enough to read TIME_LOW and TIME_HIGH either side of an > overflow of the lower half, it will see time be in the future, before > jumping backwards on the next read, and Linux currently relies on the > atomicity guaranteed by the spec so is affected by this. Fix this > violation of the spec by caching the correct value for TIME_HIGH > whenever TIME_LOW is read, and returning that value for any TIME_HIGH > read. > > Signed-off-by: Jessica Clarke <jrt...@jrtc27.com> > --- > Changes since v1: > > * Add time_high to goldfish_rtc_vmstate and increment version. > > hw/rtc/goldfish_rtc.c | 17 ++++++++++++++--- > include/hw/rtc/goldfish_rtc.h | 1 + > 2 files changed, 15 insertions(+), 3 deletions(-)
Reviewed-by: Richard Henderson <richard.hender...@linaro.org> r~
