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

From	Marc Zyngier <marc.zyngier@arm.com>
Newsgroups	linux.kernel
Subject	Re: [PATCH] arm64: KVM: VHE: reset PSTATE.UAO when switch to host
Date	2017-09-07 12:20 +0200
Message-ID	<un24G-71m-25@gated-at.bofh.it> (permalink)
References	<umXHH-3QW-3@gated-at.bofh.it> <un1ii-6qW-5@gated-at.bofh.it> <un1UZ-6Xn-5@gated-at.bofh.it>
Organization	ARM Ltd

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On 07/09/17 11:05, gengdongjiu wrote:
> Hi James,
> 
> On 2017/9/7 17:20, James Morse wrote:
>> Hi Dongjiu Geng,
>>
>> On 07/09/17 06:54, Dongjiu Geng wrote:
>>> In VHE mode, host kernel runs in the EL2 and can enable
>>> 'User Access Override' when fs==KERNEL_DS so that it can
>>> access kernel memory. However, PSTATE.UAO is set to 0 on
>>> an exception taken from EL1 to EL2. Thus when VHE is used
>>> and exception taken from a guest UAO will be disabled and
>>> host will use the incorrect PSTATE.UAO. So check and reset
>>> the PSTATE.UAO when switching to host.
>>
>> This would only be a problem if KVM were calling into world-switch with
>> fs==KERNEL_DS. I can't see where this happens.
>  Not only KVM, may also kernel sets the fs == KERNEL_DS before calling into world-switch

How? Please describe the exact sequence of event that lead to this
situation with the current code base.

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

Thread

[PATCH] arm64: KVM: VHE: reset PSTATE.UAO when switch to host Dongjiu Geng <gengdongjiu@huawei.com> - 2017-09-07 07:40 +0200
  Re: [PATCH] arm64: KVM: VHE: reset PSTATE.UAO when switch to host James Morse <james.morse@arm.com> - 2017-09-07 11:30 +0200
    Re: [PATCH] arm64: KVM: VHE: reset PSTATE.UAO when switch to host gengdongjiu <gengdongjiu@huawei.com> - 2017-09-07 12:10 +0200
      Re: [PATCH] arm64: KVM: VHE: reset PSTATE.UAO when switch to host Marc Zyngier <marc.zyngier@arm.com> - 2017-09-07 12:20 +0200
        Re: [PATCH] arm64: KVM: VHE: reset PSTATE.UAO when switch to host gengdongjiu <gengdongjiu@huawei.com> - 2017-09-07 14:00 +0200
          Re: [PATCH] arm64: KVM: VHE: reset PSTATE.UAO when switch to host Marc Zyngier <marc.zyngier@arm.com> - 2017-09-07 14:10 +0200

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