linux-kernel - Re: [PATCH 02/16] KVM: arm64: Don't issue CMOs when the physical address is invalid

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Date:   Tue, 27 Jul 2021 19:10:45 +0100
From:   Will Deacon <will@...nel.org>
To:     Marc Zyngier <maz@...nel.org>
Cc:     linux-arm-kernel@...ts.infradead.org, kvmarm@...ts.cs.columbia.edu,
        kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        qperret@...gle.com, dbrazdil@...gle.com,
        Srivatsa Vaddagiri <vatsa@...eaurora.org>,
        Shanker R Donthineni <sdonthineni@...dia.com>,
        James Morse <james.morse@....com>,
        Suzuki K Poulose <suzuki.poulose@....com>,
        Alexandru Elisei <alexandru.elisei@....com>,
        kernel-team@...roid.com
Subject: Re: [PATCH 02/16] KVM: arm64: Don't issue CMOs when the physical
 address is invalid

On Thu, Jul 15, 2021 at 05:31:45PM +0100, Marc Zyngier wrote:
> Make sure we don't issue CMOs when mapping something that
> is not a memory address in the S2 page tables.
> 
> Signed-off-by: Marc Zyngier <maz@...nel.org>
> ---
>  arch/arm64/kvm/hyp/pgtable.c | 16 ++++++++++------
>  1 file changed, 10 insertions(+), 6 deletions(-)
> 
> diff --git a/arch/arm64/kvm/hyp/pgtable.c b/arch/arm64/kvm/hyp/pgtable.c
> index 05321f4165e3..a5874ebd0354 100644
> --- a/arch/arm64/kvm/hyp/pgtable.c
> +++ b/arch/arm64/kvm/hyp/pgtable.c
> @@ -619,12 +619,16 @@ static int stage2_map_walker_try_leaf(u64 addr, u64 end, u32 level,
>  	}
>  
>  	/* Perform CMOs before installation of the guest stage-2 PTE */
> -	if (mm_ops->dcache_clean_inval_poc && stage2_pte_cacheable(pgt, new))
> -		mm_ops->dcache_clean_inval_poc(kvm_pte_follow(new, mm_ops),
> -						granule);
> -
> -	if (mm_ops->icache_inval_pou && stage2_pte_executable(new))
> -		mm_ops->icache_inval_pou(kvm_pte_follow(new, mm_ops), granule);
> +	if (kvm_phys_is_valid(phys)) {
> +		if (mm_ops->dcache_clean_inval_poc &&
> +		    stage2_pte_cacheable(pgt, new))
> +			mm_ops->dcache_clean_inval_poc(kvm_pte_follow(new,
> +								      mm_ops),
> +						       granule);
> +		if (mm_ops->icache_inval_pou && stage2_pte_executable(new))
> +			mm_ops->icache_inval_pou(kvm_pte_follow(new, mm_ops),
> +						 granule);
> +	}

Given that this check corresponds to checking the validity of 'new', I
wonder whether we'd be better off pushing the validity checks down into
stage2_pte_{cacheable,executable}()?

I.e. have stage2_pte_cacheable() return false if !kvm_pte_valid()

Will