linux-kernel - Re: [PATCH v4 05/10] KVM: arm64: Support stolen time reporting via shared structure

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Date:   Tue, 3 Sep 2019 17:14:18 +0800
From:   Zenghui Yu <yuzenghui@...wei.com>
To:     Steven Price <steven.price@....com>, Marc Zyngier <maz@...nel.org>,
        "Will Deacon" <will@...nel.org>,
        <linux-arm-kernel@...ts.infradead.org>,
        <kvmarm@...ts.cs.columbia.edu>
CC:     <linux-kernel@...r.kernel.org>, <kvm@...r.kernel.org>,
        Catalin Marinas <catalin.marinas@....com>,
        <linux-doc@...r.kernel.org>, Russell King <linux@...linux.org.uk>,
        Paolo Bonzini <pbonzini@...hat.com>
Subject: Re: [PATCH v4 05/10] KVM: arm64: Support stolen time reporting via
 shared structure

On 2019/8/30 16:42, Steven Price wrote:
> Implement the service call for configuring a shared structure between a
> VCPU and the hypervisor in which the hypervisor can write the time
> stolen from the VCPU's execution time by other tasks on the host.
> 
> The hypervisor allocates memory which is placed at an IPA chosen by user
> space.

It seems that no allocation happens in the hypervisor code.  User space
will do it instead?

> The hypervisor then updates the shared structure using
> kvm_put_guest() to ensure single copy atomicity of the 64-bit value
> reporting the stolen time in nanoseconds.
> 
> Whenever stolen time is enabled by the guest, the stolen time counter is
> reset.
> 
> The stolen time itself is retrieved from the sched_info structure
> maintained by the Linux scheduler code. We enable SCHEDSTATS when
> selecting KVM Kconfig to ensure this value is meaningful.
> 
> Signed-off-by: Steven Price <steven.price@....com>

Thanks,
zenghui