linux-kernel - Re: [PATCH] x86: convert x86_platform

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Message-ID: <ae24f18e-9a48-b6c0-9073-95121a444b53@oracle.com>
Date:   Fri, 13 Oct 2017 16:45:27 -0400
From:   Boris Ostrovsky <boris.ostrovsky@...cle.com>
To:     Arnd Bergmann <arnd@...db.de>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>, x86@...nel.org
Cc:     y2038@...ts.linaro.org, Paolo Bonzini <pbonzini@...hat.com>,
        Radim Krčmář <rkrcmar@...hat.com>,
        Juergen Gross <jgross@...e.com>,
        Marcos Paulo de Souza <marcos.souza.org@...il.com>,
        Dmitry Torokhov <dmitry.torokhov@...il.com>,
        John Stultz <john.stultz@...aro.org>,
        linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        xen-devel@...ts.xenproject.org
Subject: Re: [PATCH] x86: convert x86_platform_ops to timespec64

On 10/13/2017 02:37 PM, Arnd Bergmann wrote:
> The x86 platform operations are fairly isolated, so we can
> change them from using timespec to timespec64. I checked that
> All the users and callers are safe, and there is only one
> critical function that is broken beyond 2106:
>
> pvclock_read_wallclock() uses a 32-bit number of seconds since
> the epoch to communicate the boot time between host and guest
> in a virtual environment. This will work until 2106, but we
> should ideally find a replacement anyway. I've added a comment
> about it there.
>
> Signed-off-by: Arnd Bergmann <arnd@...db.de>
> ---
>  arch/x86/include/asm/intel_mid_vrtc.h        |  4 ++--
>  arch/x86/include/asm/mc146818rtc.h           |  4 ++--
>  arch/x86/include/asm/pvclock.h               |  2 +-
>  arch/x86/include/asm/x86_init.h              |  6 +++---
>  arch/x86/kernel/kvmclock.c                   |  4 ++--
>  arch/x86/kernel/pvclock.c                    | 12 +++++++++---
>  arch/x86/kernel/rtc.c                        | 16 ++++++++--------
>  arch/x86/platform/intel-mid/intel_mid_vrtc.c | 10 +++++-----
>  arch/x86/xen/time.c                          | 10 +++++-----
>  9 files changed, 37 insertions(+), 31 deletions(-)

Xen bits:
Reviewed-by: Boris Ostrovsky <boris.ostrovsky@...cle.com>

with a couple of nits:

> @@ -136,11 +136,17 @@ void pvclock_read_wallclock(struct pvclock_wall_clock *wall_clock,
>  		rmb();		/* fetch time before checking version */
>  	} while ((wall_clock->version & 1) || (version != wall_clock->version));
>  
> +	/*
> +	 * Note: wall_clock->sec is a u32 value, so it can only store dates
> +	 * between 1970 and 2106. To allow times beyond that, we need to
> +	 * create a new hypercall interface with an extended pvclock_wall_clock
> +	 * structure like ARM has.
> +	 */

I think this comment block should be moved up above 'now.tv_sec  =
wall_clock->sec;'


>  	delta = pvclock_clocksource_read(vcpu_time);	/* time since system boot */
>  	delta += now.tv_sec * (u64)NSEC_PER_SEC + now.tv_nsec;

Now that tv_sec is a 64-bit quantity the cast can be dropped.

-boris

>  
>  	now.tv_nsec = do_div(delta, NSEC_PER_SEC);
>  	now.tv_sec = delta;
>  
> -	set_normalized_timespec(ts, now.tv_sec, now.tv_nsec);
> +	set_normalized_timespec64(ts, now.tv_sec, now.tv_nsec);
>  }
>