linux-kernel - Re: [PATCH] arm64: KVM: VHE: save and restore some PSTATE bits

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Date:   Wed, 6 Sep 2017 09:17:41 +0100
From:   Marc Zyngier <marc.zyngier@....com>
To:     gengdongjiu <gengdongjiu@...wei.com>,
        "christoffer.dall@...aro.org" <christoffer.dall@...aro.org>,
        "pbonzini@...hat.com" <pbonzini@...hat.com>,
        "rkrcmar@...hat.com" <rkrcmar@...hat.com>,
        "vladimir.murzin@....com" <vladimir.murzin@....com>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "kvmarm@...ts.cs.columbia.edu" <kvmarm@...ts.cs.columbia.edu>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Cc:     James Morse <James.Morse@....com>
Subject: Re: [PATCH] arm64: KVM: VHE: save and restore some PSTATE bits

On 05/09/17 19:58, gengdongjiu wrote:
> when exit from guest, some host PSTATE bits may be lost, such as
> PSTATE.PAN or PSTATE.UAO. It is because host and hypervisor all run
> in the EL2, host PSTATE value cannot be saved and restored via
> SPSR_EL2. So if guest has changed the PSTATE, host continues with
> a wrong value guest has set.
> 
> Signed-off-by: Dongjiu Geng <gengdongjiu@...wei.com>
> Signed-off-by: Haibin Zhang <zhanghaibin7@...wei.com>
> ---
>  arch/arm64/include/asm/kvm_host.h |  8 +++++++
>  arch/arm64/include/asm/kvm_hyp.h  |  2 ++
>  arch/arm64/include/asm/sysreg.h   | 23 +++++++++++++++++++
>  arch/arm64/kvm/hyp/entry.S        |  2 --
>  arch/arm64/kvm/hyp/switch.c       | 24 ++++++++++++++++++--
>  arch/arm64/kvm/hyp/sysreg-sr.c    | 48 ++++++++++++++++++++++++++++++++++++---
>  6 files changed, 100 insertions(+), 7 deletions(-)
> 
> diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
> index e923b58..cba7d3e 100644
> --- a/arch/arm64/include/asm/kvm_host.h
> +++ b/arch/arm64/include/asm/kvm_host.h
> @@ -193,6 +193,12 @@ struct kvm_cpu_context {
>  	};
>  };
>  
> +struct kvm_cpu_host_pstate {
> +	u64 daif;
> +	u64 uao;
> +	u64 pan;
> +};

I love it. This is the most expensive way of saving/restoring a single
32bit value.

More seriously, please see the discussion between James and Christoffer
there[1]. I expect James to address the PAN/UAO states together with the
debug state in the next iteration of his patch.

Thanks,

	M.

[1] https://www.spinics.net/lists/arm-kernel/msg599798.html
-- 
Jazz is not dead. It just smells funny...