lkml.org 
[lkml]   [2021]   [Jan]   [26]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
SubjectRe: [patch 1/8] rtc: mc146818: Prevent reading garbage - bug
From
Date
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@linutronix.de>
> 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@digikod.net>
> Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
> ---
> 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@linux.microsoft.com>

\
 
 \ /
  Last update: 2021-01-26 15:23    [W:0.087 / U:1.300 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site