linux-kernel - Re: [PATCHv4 15/28] x86/vdso: Add offsets page in vvar

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Message-ID: <cc38a049-aa49-4290-d721-e0adc5d25491@gmail.com>
Date:   Sun, 16 Jun 2019 18:49:47 +0100
From:   Dmitry Safonov <0x7f454c46@...il.com>
To:     Thomas Gleixner <tglx@...utronix.de>,
        Dmitry Safonov <dima@...sta.com>
Cc:     linux-kernel@...r.kernel.org, Andrei Vagin <avagin@...nvz.org>,
        Adrian Reber <adrian@...as.de>,
        Andy Lutomirski <luto@...nel.org>,
        Arnd Bergmann <arnd@...db.de>,
        Christian Brauner <christian.brauner@...ntu.com>,
        Cyrill Gorcunov <gorcunov@...nvz.org>,
        "Eric W. Biederman" <ebiederm@...ssion.com>,
        "H. Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...hat.com>,
        Jann Horn <jannh@...gle.com>, Jeff Dike <jdike@...toit.com>,
        Oleg Nesterov <oleg@...hat.com>,
        Pavel Emelyanov <xemul@...tuozzo.com>,
        Shuah Khan <shuah@...nel.org>,
        Vincenzo Frascino <vincenzo.frascino@....com>,
        containers@...ts.linux-foundation.org, criu@...nvz.org,
        linux-api@...r.kernel.org, x86@...nel.org,
        Andrei Vagin <avagin@...il.com>
Subject: Re: [PATCHv4 15/28] x86/vdso: Add offsets page in vvar

On 6/14/19 2:58 PM, Thomas Gleixner wrote:
> On Wed, 12 Jun 2019, Dmitry Safonov wrote:
>>  
>> +#ifdef CONFIG_TIME_NS
>> +notrace static __always_inline void clk_to_ns(clockid_t clk, struct timespec *ts)
>> +{
>> +	struct timens_offsets *timens = (struct timens_offsets *) &timens_page;
>> +	struct timespec64 *offset64;
>> +
>> +	switch (clk) {
>> +	case CLOCK_MONOTONIC:
>> +	case CLOCK_MONOTONIC_COARSE:
>> +	case CLOCK_MONOTONIC_RAW:
>> +		offset64 = &timens->monotonic;
>> +		break;
>> +	case CLOCK_BOOTTIME:
>> +		offset64 = &timens->boottime;
>> +	default:
>> +		return;
>> +	}
>> +
>> +	ts->tv_nsec += offset64->tv_nsec;
>> +	ts->tv_sec += offset64->tv_sec;
>> +	if (ts->tv_nsec >= NSEC_PER_SEC) {
>> +		ts->tv_nsec -= NSEC_PER_SEC;
>> +		ts->tv_sec++;
>> +	}
>> +	if (ts->tv_nsec < 0) {
>> +		ts->tv_nsec += NSEC_PER_SEC;
>> +		ts->tv_sec--;
>> +	}
> 
> I had to think twice why adding the offset (which can be negative) can
> never result in negative time being returned. A comment explaining this
> would be appreciated.
> 
> As I'm planning to merge Vincezos VDSO consolidation into 5.3, can you
> please start to work on top of his series, which should be available as
> final v7 next week hopefully.

Yes, will rebase on the top of his series.

Thanks much,
          Dmitry