linux-kernel - Re: [PATCH] kvm: x86: fix kvmclock update protocol

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Message-ID: <20150423152405.GA1927@potion.brq.redhat.com>
Date:	Thu, 23 Apr 2015 17:24:05 +0200
From:	Radim Krčmář <rkrcmar@...hat.com>
To:	Paolo Bonzini <pbonzini@...hat.com>
Cc:	linux-kernel@...r.kernel.org, kvm@...r.kernel.org, luto@...nel.org,
	mtosatti@...hat.com
Subject: Re: [PATCH] kvm: x86: fix kvmclock update protocol

2015-04-23 13:46+0200, Paolo Bonzini:
> From: Radim Krčmář <rkrcmar@...hat.com>
> 
> The kvmclock spec says that the host will increment a version field to
> an odd number, then update stuff, then increment it to an even number.
> The host is buggy and doesn't do this, and the result is observable
> when one vcpu reads another vcpu's kvmclock data.
> 
> There's no good way for a guest kernel to keep its vdso from reading
> a different vcpu's kvmclock data, but we don't need to care about
> changing VCPUs as long as we read a consistent data from kvmclock.
> (VCPU can change outside of this loop too, so it doesn't matter if we
> return a value not fit for this VCPU.)
> 
> Based on a patch by Radim Krčmář.
> 
> Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>
> ---

Nice,

Reviewed-by: Radim Krčmář <rkrcmar@...hat.com>
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