linux-kernel - Re: [PATCH v1 07/24] kvm: arm64: Create nVHE copy of cpu_logical

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Date:   Tue, 10 Nov 2020 15:24:52 +0000
From:   Marc Zyngier <maz@...nel.org>
To:     David Brazdil <dbrazdil@...gle.com>
Cc:     kvmarm@...ts.cs.columbia.edu, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org, James Morse <james.morse@....com>,
        Julien Thierry <julien.thierry.kdev@...il.com>,
        Suzuki K Poulose <suzuki.poulose@....com>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>, 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>,
        Quentin Perret <qperret@...gle.com>,
        Andrew Scull <ascull@...gle.com>,
        Andrew Walbran <qwandor@...gle.com>, kernel-team@...roid.com
Subject: Re: [PATCH v1 07/24] kvm: arm64: Create nVHE copy of cpu_logical_map

On 2020-11-09 11:32, David Brazdil wrote:
> When KVM starts validating host's PSCI requests, it will need to map
> MPIDR back to the CPU ID. To this end, copy cpu_logical_map into nVHE
> hyp memory when KVM is initialized.
> 
> Only copy the information for CPUs that are online at the point of KVM
> initialization so that KVM rejects CPUs whose features were not checked
> against the finalized capabilities.
> 
> Signed-off-by: David Brazdil <dbrazdil@...gle.com>
> ---
>  arch/arm64/kvm/arm.c             | 17 +++++++++++++++++
>  arch/arm64/kvm/hyp/nvhe/percpu.c | 16 ++++++++++++++++
>  2 files changed, 33 insertions(+)
> 
> diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c
> index 9ba9db2aa7f8..b85b4294b72d 100644
> --- a/arch/arm64/kvm/arm.c
> +++ b/arch/arm64/kvm/arm.c
> @@ -1481,6 +1481,21 @@ static inline void hyp_cpu_pm_exit(void)
>  }
>  #endif
> 
> +static void init_cpu_logical_map(void)
> +{
> +	extern u64 kvm_nvhe_sym(__cpu_logical_map)[NR_CPUS];
> +	int cpu;
> +
> +	/*
> +	 * Copy the MPIDR <-> logical CPU ID mapping to hyp.
> +	 * Only copy the set of online CPUs whose features have been chacked
> +	 * against the finalized system capabilities. The hypervisor will not
> +	 * allow any other CPUs from the `possible` set to boot.
> +	 */
> +	for_each_online_cpu(cpu)
> +		CHOOSE_NVHE_SYM(__cpu_logical_map)[cpu] = cpu_logical_map(cpu);
> +}
> +
>  static int init_common_resources(void)
>  {
>  	return kvm_set_ipa_limit();
> @@ -1659,6 +1674,8 @@ static int init_hyp_mode(void)
>  		}
>  	}
> 
> +	init_cpu_logical_map();
> +
>  	return 0;
> 
>  out_err:
> diff --git a/arch/arm64/kvm/hyp/nvhe/percpu.c 
> b/arch/arm64/kvm/hyp/nvhe/percpu.c
> index 5fd0c5696907..d0b9dbc2df45 100644
> --- a/arch/arm64/kvm/hyp/nvhe/percpu.c
> +++ b/arch/arm64/kvm/hyp/nvhe/percpu.c
> @@ -8,6 +8,22 @@
>  #include <asm/kvm_hyp.h>
>  #include <asm/kvm_mmu.h>
> 
> +/*
> + * nVHE copy of data structures tracking available CPU cores.
> + * Only entries for CPUs that were online at KVM init are populated.
> + * Other CPUs should not be allowed to boot because their features 
> were
> + * not checked against the finalized system capabilities.
> + */
> +u64 __ro_after_init __cpu_logical_map[NR_CPUS] = { [0 ... NR_CPUS-1]
> = INVALID_HWID };

I'm not sure what __ro_after_init means once we get S2 isolation.

> +
> +u64 cpu_logical_map(int cpu)

nit: is there any reason why "cpu" cannot be unsigned? The thought
of a negative CPU number makes me shiver...

> +{
> +	if (cpu < 0 || cpu >= ARRAY_SIZE(__cpu_logical_map))
> +		hyp_panic();
> +
> +	return __cpu_logical_map[cpu];
> +}
> +
>  unsigned long __hyp_per_cpu_offset(unsigned int cpu)
>  {
>  	unsigned long *cpu_base_array;

Overall, this patch would make more sense closer it its use case
(in patch 19). I also don't understand why this lives in percpu.c...

Thanks,

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