linux-kernel - Re: [PATCH] [v3] x86: Convert x86_platform

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Date:   Fri, 27 Apr 2018 23:21:29 +0100
From:   Joao Martins <joao.m.martins@...cle.com>
To:     Arnd Bergmann <arnd@...db.de>
Cc:     Thomas Gleixner <tglx@...utronix.de>, y2038@...ts.linaro.org,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>, x86@...nel.org,
        Jan Kiszka <jan.kiszka@...mens.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Radim Krčmář <rkrcmar@...hat.com>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Juergen Gross <jgross@...e.com>,
        "Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Borislav Petkov <bp@...e.de>,
        Andy Lutomirski <luto@...nel.org>,
        John Stultz <john.stultz@...aro.org>,
        linux-kernel@...r.kernel.org, jailhouse-dev@...glegroups.com,
        kvm@...r.kernel.org, xen-devel@...ts.xenproject.org
Subject: Re: [PATCH] [v3] x86: Convert x86_platform_ops to timespec64

On 04/27/2018 09:13 PM, Arnd Bergmann wrote:
> diff --git a/arch/x86/kernel/pvclock.c b/arch/x86/kernel/pvclock.c
> index 761f6af6efa5..637982efecd8 100644
> --- a/arch/x86/kernel/pvclock.c
> +++ b/arch/x86/kernel/pvclock.c
> @@ -123,28 +123,35 @@ u64 pvclock_clocksource_read(struct pvclock_vcpu_time_info *src)
>  
>  void pvclock_read_wallclock(struct pvclock_wall_clock *wall_clock,
>  			    struct pvclock_vcpu_time_info *vcpu_time,
> -			    struct timespec *ts)
> +			    struct timespec64 *ts)
>  {
>  	u32 version;
>  	u64 delta;
> -	struct timespec now;
> +	struct timespec64 now;
>  
>  	/* get wallclock at system boot */
>  	do {
>  		version = wall_clock->version;
>  		rmb();		/* fetch version before time */
> +		/*
> +		 * 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.
> +		 */
>  		now.tv_sec  = wall_clock->sec;

IIUC the interface you're probably speaking about is common to both ARM and x86
on Xen[*] (since Xen 4.6) i.e.

	now.tv_sec  = ((uint64_t)s->wc_sec_hi << 32) | s->wc_sec;

s representing struct shared_info like on ARM (there's a 32-bit hole where
wc_sec_hi is placed on x86_64/ARM). Except on x86 32-bit guests wc_sec_hi is
located elsewhere.

	Joao

[*]
https://xenbits.xen.org/docs/4.6-testing/hypercall/x86_64/include,public,xen.h.html#incontents_startofday_shared