linux-kernel - Re: [PATCH] arm64: KVM: VHE: reset PSTATE.UAO when switch to host

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Date:   Fri, 8 Sep 2017 13:33:06 +0000
From:   gengdongjiu <gengdongjiu@...wei.com>
To:     Marc Zyngier <marc.zyngier@....com>
CC:     James Morse <james.morse@....com>,
        "christoffer.dall@...aro.org" <christoffer.dall@...aro.org>,
        "vladimir.murzin@....com" <vladimir.murzin@....com>,
        "rkrcmar@...hat.com" <rkrcmar@...hat.com>,
        "catalin.marinas@....com" <catalin.marinas@....com>,
        "shankerd@...eaurora.org" <shankerd@...eaurora.org>,
        "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>,
        "Zhanghaibin (Euler)" <zhanghaibin7@...wei.com>,
        Huangshaoyu <huangshaoyu@...wei.com>
Subject: Re: [PATCH] arm64: KVM: VHE: reset PSTATE.UAO when switch to host

Hi Marc,

> 
> On 08/09/17 10:05, gengdongjiu wrote:
> > Marc,
> >    Thanks for reply.
> >
> > On 2017/9/8 16:21, Marc Zyngier wrote:
> >>> Marc,
> >>>
> >>> sorry I have another question for the PAN.
[...]
> There cannot be any userspace mapping at EL2 when non-VHE, so there cannot be any valid PAN setting. I repeat: there is not such thing as
> PAN at EL2 when HCR_EL2.E2H==0. This bit *has no effect*. Just read the documentation (ARM DDI 0487B.a, D4.4.2).

Thanks Marc's comments, I completely agree with you, I understand the architecture, in non-VHE, user space mapping only exists at EL1 and pointed by the ttbr0_el1.
In the EL1, it uses ttbr0_el1 to point userspace page table, uses ttbr1_el1 to point kernel mapping.
In the EL2, it uses ttbr0_el2 or vttbr_el2 for address translation, cannot use the ttbr0_el1. 

> 
> If you're going to change this kind of code, please start by understanding the architecture.

OK, so I plant to remove the PAN setting at EL2 in non-VHE.

> 
> 	M.
> --
> Jazz is not dead. It just smells funny...