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Date:   Mon, 23 Nov 2020 18:01:13 +0000
Message-ID: <878sas54wm.wl-maz@kernel.org>
From:   Marc Zyngier <maz@kernel.org>
To:     David Brazdil <dbrazdil@google.com>
Cc:     kvmarm@lists.cs.columbia.edu, linux-arm-kernel@lists.infradead.org,
        linux-kernel@vger.kernel.org, James Morse <james.morse@arm.com>,
        Julien Thierry <julien.thierry.kdev@gmail.com>,
        Suzuki K Poulose <suzuki.poulose@arm.com>,
        Catalin Marinas <catalin.marinas@arm.com>,
        Will Deacon <will@kernel.org>, Dennis Zhou <dennis@kernel.org>,
        Tejun Heo <tj@kernel.org>, Christoph Lameter <cl@linux.com>,
        Mark Rutland <mark.rutland@arm.com>,
        Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>,
        Quentin Perret <qperret@google.com>,
        Andrew Scull <ascull@google.com>,
        Andrew Walbran <qwandor@google.com>, kernel-team@android.com,
        Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>,
        Sudeep Holla <sudeep.holla@arm.com>
Subject: Re: [PATCH v2 00/24] Opt-in always-on nVHE hypervisor
In-Reply-To: <20201116204318.63987-1-dbrazdil@google.com>
References: <20201116204318.63987-1-dbrazdil@google.com>
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Hi David,

On Mon, 16 Nov 2020 20:42:54 +0000,
David Brazdil <dbrazdil@google.com> wrote:
> 
> As we progress towards being able to keep guest state private to the
> host running nVHE hypervisor, this series allows the hypervisor to
> install itself on newly booted CPUs before the host is allowed to run
> on them.
> 
> All functionality described below is opt-in, guarded by an early param
> 'kvm-arm.protected'. Future patches specific to the new "protected" mode
> should be hidden behind the same param.
> 
> The hypervisor starts trapping host SMCs and intercepting host's PSCI
> CPU_ON/SUSPEND calls. It replaces the host's entry point with its own,
> initializes the EL2 state of the new CPU and installs the nVHE hyp vector
> before ERETing to the host's entry point.
> 
> The kernel checks new cores' features against the finalized system
> capabilities. To avoid the need to move this code/data to EL2, the
> implementation only allows to boot cores that were online at the time of
> KVM initialization and therefore had been checked already.
> 
> Other PSCI SMCs are forwarded to EL3, though only the known set of SMCs
> implemented in the kernel is allowed. Non-PSCI SMCs are also forwarded
> to EL3. Future changes will need to ensure the safety of all SMCs wrt.
> private guests.
> 
> The host is still allowed to reset EL2 back to the stub vector, eg. for
> hibernation or kexec, but will not disable nVHE when there are no VMs.

I have now been through the whole series, and I don't think there is
anything really major (although I haven't tried it yet).

I think it would benefit from being rebased on top of kvmarm/queue, as
it'd give you the opportunity to replace a number of per-CPU state
fields with global function pointers. Another thing is that we seem to
have diverging interpretations of the PSCI spec when it comes to
CPU_SUSPEND.

Finally, please include the PSCI maintainers in your next posting, as
I'll need their Ack to pick the first few patches.

Thanks,

	M.

-- 
Without deviation from the norm, progress is not possible.