linux-kernel - Re: [PATCH v3 06/23] kvm: arm64: Add kvm-arm.protected early kernel parameter

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Message-ID: <20201201131913.u7m2eifvtus74dra@google.com>
Date:   Tue, 1 Dec 2020 13:19:13 +0000
From:   David Brazdil <dbrazdil@...gle.com>
To:     Sudeep Holla <sudeep.holla@....com>
Cc:     kvmarm@...ts.cs.columbia.edu, Jonathan Corbet <corbet@....net>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>, Marc Zyngier <maz@...nel.org>,
        James Morse <james.morse@....com>,
        Julien Thierry <julien.thierry.kdev@...il.com>,
        Suzuki K Poulose <suzuki.poulose@....com>,
        Dennis Zhou <dennis@...nel.org>, Tejun Heo <tj@...nel.org>,
        Christoph Lameter <cl@...ux.com>,
        Mark Rutland <mark.rutland@....com>,
        Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, kernel-team@...roid.com
Subject: Re: [PATCH v3 06/23] kvm: arm64: Add kvm-arm.protected early kernel
 parameter

Hey Sudeep,

> > diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
> > index 526d65d8573a..06c89975c29c 100644
> > --- a/Documentation/admin-guide/kernel-parameters.txt
> > +++ b/Documentation/admin-guide/kernel-parameters.txt
> > @@ -2259,6 +2259,11 @@
> >  			for all guests.
> >  			Default is 1 (enabled) if in 64-bit or 32-bit PAE mode.
> >  
> > +	kvm-arm.protected=
> > +			[KVM,ARM] Allow spawning protected guests whose state
> > +			is kept private from the host. Only valid for non-VHE.
> > +			Default is 0 (disabled).
> > +
> 
> Sorry for being pedantic. Can we reword this to say valid for
> !CONFIG_ARM64_VHE ? I read this as valid only for non-VHE hardware, it may
> be just me, but if you agree please update so that it doesn't give remote
> idea that it is not valid on VHE enabled hardware.
> 
> I was trying to run this on the hardware and was trying to understand the
> details on how to do that.

I see what you're saying, but !CONFIG_ARM64_VHE isn't accurate either. The
option makes sense if:
  1) all cores booted in EL2
     == is_hyp_mode_available()
  2) ID_AA64MMFR1_EL1.VH=0 or !CONFIG_ARM64_VHE
     == !is_kernel_in_hyp_mode()

The former feels implied for KVM, the latter could be 'Valid if the kernel
is running in EL1'? WDYT?

-David