linux-kernel - Re: [PATCH] kvm: x86: use getboottime64

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Message-ID: <b54f1377-d7db-0b0c-7b27-e9a785491fc5@redhat.com>
Date:	Thu, 23 Jun 2016 19:15:15 +0200
From:	Paolo Bonzini <pbonzini@...hat.com>
To:	Arnd Bergmann <arnd@...db.de>,
	Radim Krčmář <rkrcmar@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>, x86@...nel.org
Cc:	y2038@...ts.linaro.org,
	Xiao Guangrong <guangrong.xiao@...ux.intel.com>,
	Andrey Smetanin <asmetanin@...tuozzo.com>,
	"Denis V. Lunev" <den@...nvz.org>,
	Haozhong Zhang <haozhong.zhang@...el.com>,
	Feng Wu <feng.wu@...el.com>,
	Steve Rutherford <srutherford@...gle.com>,
	Andy Lutomirski <luto@...nel.org>, kvm@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] kvm: x86: use getboottime64



On 17/06/2016 17:48, Arnd Bergmann wrote:
> KVM reads the current boottime value as a struct timespec in order to
> calculate the guest wallclock time, resulting in an overflow in 2038
> on 32-bit systems.
> 
> The data then gets passed as an unsigned 32-bit number to the guest,
> and that in turn overflows in 2106.
> 
> We cannot do much about the second overflow, which affects both 32-bit
> and 64-bit hosts, but we can ensure that they both behave the same
> way and don't overflow until 2106, by using getboottime64() to read
> a timespec64 value.
> 
> Signed-off-by: Arnd Bergmann <arnd@...db.de>
> ---
>  arch/x86/kvm/x86.c | 10 +++++-----
>  1 file changed, 5 insertions(+), 5 deletions(-)
> 
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 53241618e3c9..f79c86510408 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -1163,7 +1163,7 @@ static void kvm_write_wall_clock(struct kvm *kvm, gpa_t wall_clock)
>  	int version;
>  	int r;
>  	struct pvclock_wall_clock wc;
> -	struct timespec boot;
> +	struct timespec64 boot;
>  
>  	if (!wall_clock)
>  		return;
> @@ -1186,13 +1186,13 @@ static void kvm_write_wall_clock(struct kvm *kvm, gpa_t wall_clock)
>  	 * wall clock specified here.  guest system time equals host
>  	 * system time for us, thus we must fill in host boot time here.
>  	 */
> -	getboottime(&boot);
> +	getboottime64(&boot);
>  
>  	if (kvm->arch.kvmclock_offset) {
> -		struct timespec ts = ns_to_timespec(kvm->arch.kvmclock_offset);
> -		boot = timespec_sub(boot, ts);
> +		struct timespec64 ts = ns_to_timespec64(kvm->arch.kvmclock_offset);
> +		boot = timespec64_sub(boot, ts);
>  	}
> -	wc.sec = boot.tv_sec;
> +	wc.sec = (u32)boot.tv_sec; /* overflow in 2106 guest time */
>  	wc.nsec = boot.tv_nsec;
>  	wc.version = version;
>  
> 

Queued, thanks.

Paolo