Re: [PATCH v2 14/24] KVM: arm64: Add pcpu fixmap infrastructure at EL2

From: Vincent Donnefort <vdonnefort@google.com>
To: Will Deacon <will@kernel.org>
Cc: kvmarm@lists.cs.columbia.edu, Ard Biesheuvel <ardb@kernel.org>,
	Sean Christopherson <seanjc@google.com>,
	Alexandru Elisei <alexandru.elisei@arm.com>,
	Andy Lutomirski <luto@amacapital.net>,
	Catalin Marinas <catalin.marinas@arm.com>,
	James Morse <james.morse@arm.com>,
	Chao Peng <chao.p.peng@linux.intel.com>,
	Quentin Perret <qperret@google.com>,
	Suzuki K Poulose <suzuki.poulose@arm.com>,
	Michael Roth <michael.roth@amd.com>,
	Mark Rutland <mark.rutland@arm.com>,
	Fuad Tabba <tabba@google.com>,
	Oliver Upton <oliver.upton@linux.dev>,
	Marc Zyngier <maz@kernel.org>,
	kernel-team@android.com, kvm@vger.kernel.org,
	linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH v2 14/24] KVM: arm64: Add pcpu fixmap infrastructure at EL2
Date: Tue, 19 Jul 2022 14:30:16 +0100	[thread overview]
Message-ID: <Ytax6L2BUt5ON1Dp@google.com> (raw)
In-Reply-To: <20220630135747.26983-15-will@kernel.org>

>  static struct hyp_pool host_s2_pool;
> diff --git a/arch/arm64/kvm/hyp/nvhe/mm.c b/arch/arm64/kvm/hyp/nvhe/mm.c
> index d3a3b47181de..17d689483ec4 100644
> --- a/arch/arm64/kvm/hyp/nvhe/mm.c
> +++ b/arch/arm64/kvm/hyp/nvhe/mm.c
> @@ -14,6 +14,7 @@
>  #include <nvhe/early_alloc.h>
>  #include <nvhe/gfp.h>
>  #include <nvhe/memory.h>
> +#include <nvhe/mem_protect.h>
>  #include <nvhe/mm.h>
>  #include <nvhe/spinlock.h>
>  
> @@ -24,6 +25,7 @@ struct memblock_region hyp_memory[HYP_MEMBLOCK_REGIONS];
>  unsigned int hyp_memblock_nr;
>  
>  static u64 __io_map_base;
> +static DEFINE_PER_CPU(void *, hyp_fixmap_base);
>  
>  static int __pkvm_create_mappings(unsigned long start, unsigned long size,
>  				  unsigned long phys, enum kvm_pgtable_prot prot)
> @@ -212,6 +214,76 @@ int hyp_map_vectors(void)
>  	return 0;
>  }
>  
> +void *hyp_fixmap_map(phys_addr_t phys)
> +{
> +	void *addr = *this_cpu_ptr(&hyp_fixmap_base);
> +	int ret = kvm_pgtable_hyp_map(&pkvm_pgtable, (u64)addr, PAGE_SIZE,
> +				      phys, PAGE_HYP);
> +	return ret ? NULL : addr;
> +}
> +
> +int hyp_fixmap_unmap(void)
> +{
> +	void *addr = *this_cpu_ptr(&hyp_fixmap_base);
> +	int ret = kvm_pgtable_hyp_unmap(&pkvm_pgtable, (u64)addr, PAGE_SIZE);
> +
> +	return (ret != PAGE_SIZE) ? -EINVAL : 0;
> +}
> +

I probably missed something but as the pagetable pages for this mapping are
pined, it seems impossible (currently) for this call to fail. Maybe a WARN_ON
would be more appropriate, especially the callers in the subsequent patches do
not seem to check for this function return value?

[...]

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