linux-kernel - Re: [patch 0/7] x86/kvmclock: Remove memblock dependency and further cleanups

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Message-ID: <f4071613-e151-90ff-7298-1ebc6e94c152@redhat.com>
Date:   Fri, 6 Jul 2018 19:47:24 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Thomas Gleixner <tglx@...utronix.de>,
        LKML <linux-kernel@...r.kernel.org>
Cc:     Radim Krcmar <rkrcmar@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Juergen Gross <jgross@...e.com>,
        Pavel Tatashin <pasha.tatashin@...cle.com>,
        steven.sistare@...cle.com, daniel.m.jordan@...cle.com,
        x86@...nel.org, kvm@...r.kernel.org
Subject: Re: [patch 0/7] x86/kvmclock: Remove memblock dependency and further
 cleanups

On 06/07/2018 18:13, Thomas Gleixner wrote:
> To allow early utilization of kvmclock it is required to remove the
> memblock dependency. memblock is currently used to allocate the per
> cpu data for kvmclock.
> 
> The first patch replaces the memblock with a static array sized 64bytes *
> NR_CPUS and was posted by Pavel. That patch allocates everything statically
> which is a waste when kvmclock is not used.
> 
> The rest of the series cleans up the code and converts it to per cpu
> variables but does not put the kvmclock data into the per cpu area as that
> has an issue vs. mapping the boot cpu data into the VDSO (leaks arbitrary
> data, unless page sized).
> 
> The per cpu data consists of pointers to the actual data. For the boot cpu
> a page sized array is statically allocated which can be mapped into the
> VDSO. That array is used for initializing the first 64 CPU pointers. If
> there are more CPUs the pvclock data is allocated during CPU bringup.
> 
> So this still will have some overhead when kvmclock is not in use, but
> bringing it down to zero would be a massive trainwreck and even more
> indirections.
> 
> Thanks,
> 
> 	tglx
> 
> 8<--------------
>  a/arch/x86/include/asm/kvm_guest.h |    7 
>  arch/x86/include/asm/kvm_para.h    |    1 
>  arch/x86/kernel/kvm.c              |   14 -
>  arch/x86/kernel/kvmclock.c         |  262 ++++++++++++++-----------------------
>  arch/x86/kernel/setup.c            |    4 
>  5 files changed, 105 insertions(+), 183 deletions(-)
> 
> 
> 
> 

Thanks, this is really nice.  With the small changes from my review,

Acked-by: Paolo Bonzini <pbonzini@...hat.com>

Paolo