linux-kernel - Re: [PATCH v7 9/10] KVM: arm64: docs: document KVM support of pointer authentication

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Date:   Thu, 28 Mar 2019 15:43:07 +0530
From:   Amit Daniel Kachhap <amit.kachhap@....com>
To:     Dave Martin <Dave.Martin@....com>
Cc:     Kristina Martsenko <kristina.martsenko@....com>,
        Marc Zyngier <marc.zyngier@....com>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will.deacon@....com>,
        linux-kernel@...r.kernel.org,
        Ramana Radhakrishnan <ramana.radhakrishnan@....com>,
        kvmarm@...ts.cs.columbia.edu, linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v7 9/10] KVM: arm64: docs: document KVM support of pointer
 authentication

Hi Dave,

On 3/27/19 7:20 PM, Dave Martin wrote:
> On Wed, Mar 27, 2019 at 05:19:28PM +0530, Amit Daniel Kachhap wrote:
>> Hi,
>>
>> On 3/27/19 4:14 PM, Dave Martin wrote:
>>> On Mon, Mar 25, 2019 at 08:05:49PM +0000, Kristina Martsenko wrote:
>>>> On 19/03/2019 08:30, Amit Daniel Kachhap wrote:
>>>>> This adds sections for KVM API extension for pointer authentication.
>>>>> A brief description about usage of pointer authentication for KVM guests
>>>>> is added in the arm64 documentations.
>>>>>
>>>>> Signed-off-by: Amit Daniel Kachhap <amit.kachhap@....com>
>>>>> Cc: Mark Rutland <mark.rutland@....com>
>>>>> Cc: Christoffer Dall <christoffer.dall@....com>
>>>>> Cc: Marc Zyngier <marc.zyngier@....com>
>>>>> Cc: kvmarm@...ts.cs.columbia.edu
>>>>
>>>> I think it makes sense to also update the Kconfig symbol description for
>>>> CONFIG_ARM64_PTR_AUTH, since it currently only mentions userspace
>>>> support, but now the option also enables KVM guest support.
>>>>
>>>> It's also worth mentioning that CONFIG_ARM64_VHE=y is required for guest
>>>> support.
>>>
>>> Is it worth making this dependency explicit in Kconfig?
>> Currently there is discrepancy that userspace supports ptrauth in both
>> nVHE/VHE mode and KVM guest only in VHE mode. I suppose adding explicit
>> dependency flag here makes both of them similar.
> 
> Looking at the history, for SVE this Kconfig restriction has always been
> present.  Since ptrauth initially upstreamed without an equivalent
> restriction in Kconfig, adding it now could be seen as a regression.
ok it makes sense to keep it this way.
> 
> So, maybe it's not worth it here.
> 
> You could add a separate option, say
> 
> config ARM64_PTR_AUTH_KVM
> 	bool "Pointer authentication support for KVM guests"
> 	default y
> 	depends on ARM64_PTR_AUTH && ARM64_VHE && KVM
> 
> ...but that may be overkill.
I was thinking for adding some details for this in virtualization 
section in Documentation/arm64/pointer-authentication.txt along with 
brief comment in arch/arm64/Kconfig.

Thanks,
Amit D
> 
> Cheers,
> ---Dave
>