Thanks for the fix! It boots now with a new message: rtc_cmos rtc_cmos: not accessible I tested with rtc=on and rtc=off (which didn't make a difference before this fix) on a microvm: https://github.com/qemu/qemu/blob/master/docs/system/i386/microvm.rst There is one issue with the memset though: On 26/01/2021 14:26, Thomas Gleixner wrote: > On Mon, Jan 25 2021 at 19:40, Mickaël Salaün wrote: >> After some bisecting, I found that commit 05a0302c3548 ("rtc: mc146818: >> Prevent reading garbage", this patch, introduced since v5.11-rc1) makes >> my VM hang at boot. Before this commit, I got this (and didn't notice) >> at every boot: >> rtc_cmos rtc_cmos: registered as rtc0 >> rtc_cmos rtc_cmos: hctosys: unable to read the hardware clock >> rtc_cmos rtc_cmos: alarms up to one day, 114 bytes nvram >> >> I notice that this patch creates infinite loops, which my VM falls into >> (cf. below). >>> + time->tm_sec = CMOS_READ(RTC_SECONDS); >>> + >>> + if (CMOS_READ(RTC_FREQ_SELECT) & RTC_UIP) { >>> + spin_unlock_irqrestore(&rtc_lock, flags); >>> + mdelay(1); >> >> My VM loops here. >> time->tm_sec is always 255. > > That means there is no RTC and therefore the CMOS_READ($REG) returns > 0xFF which makes the loop stuck because RTC_UIP is always set. > > Yet another proof that VIRT creates more problems than it solves. > > Fix below. > > Thanks, > > tglx > --- > Subject: rtc: mc146818: Detect and handle broken RTCs > From: Thomas Gleixner <tglx@xxxxxxxxxxxxx> > Date: Tue, 26 Jan 2021 11:38:40 +0100 > > The recent fix for handling the UIP bit unearthed another issue in the RTC > code. If the RTC is advertised but the readout is straight 0xFF because > it's not available, the old code just proceeded with crappy values, but the > new code hangs because it waits for the UIP bit to become low. > > Add a sanity check in the RTC CMOS probe function which reads the RTC_VALID > register (Register D) which should have bit 0-6 cleared. If that's not the > case then fail to register the CMOS. > > Add the same check to mc146818_get_time(), warn once when the condition > is true and invalidate the rtc_time data. > > Reported-by: Mickaël Salaün <mic@xxxxxxxxxxx> > Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx> > --- > drivers/rtc/rtc-cmos.c | 8 ++++++++ > drivers/rtc/rtc-mc146818-lib.c | 7 +++++++ > 2 files changed, 15 insertions(+) > > --- a/drivers/rtc/rtc-cmos.c > +++ b/drivers/rtc/rtc-cmos.c > @@ -805,6 +805,14 @@ cmos_do_probe(struct device *dev, struct > > spin_lock_irq(&rtc_lock); > > + /* Ensure that the RTC is accessible. Bit 0-6 must be 0! */ > + if ((CMOS_READ(RTC_VALID) & 0x7f) != 0) { > + spin_unlock_irq(&rtc_lock); > + dev_warn(dev, "not accessible\n"); > + retval = -ENXIO; > + goto cleanup1; > + } > + > if (!(flags & CMOS_RTC_FLAGS_NOFREQ)) { > /* force periodic irq to CMOS reset default of 1024Hz; > * > --- a/drivers/rtc/rtc-mc146818-lib.c > +++ b/drivers/rtc/rtc-mc146818-lib.c > @@ -21,6 +21,13 @@ unsigned int mc146818_get_time(struct rt > > again: > spin_lock_irqsave(&rtc_lock, flags); > + /* Ensure that the RTC is accessible. Bit 0-6 must be 0! */ > + if (WARN_ON_ONCE((CMOS_READ(RTC_VALID) & 0x7f) != 0)) { > + spin_unlock_irqrestore(&rtc_lock, flags); > + memset(time, 0xff, sizeof(time)); This should be: sizeof(*time) > + return 0; > + } > + > /* > * Check whether there is an update in progress during which the > * readout is unspecified. The maximum update time is ~2ms. Poll > Tested-by: Mickaël Salaün <mic@xxxxxxxxxxxxxxxxxxx>
