Re: [PATCH v6 1/4] kvm: arm64: introduce new flag for non-cacheable IO memory

From: Will Deacon <will@kernel.org>
To: ankita@nvidia.com
Cc: jgg@nvidia.com, maz@kernel.org, oliver.upton@linux.dev,
	james.morse@arm.com, suzuki.poulose@arm.com,
	yuzenghui@huawei.com, reinette.chatre@intel.com,
	surenb@google.com, stefanha@redhat.com, brauner@kernel.org,
	catalin.marinas@arm.com, mark.rutland@arm.com,
	alex.williamson@redhat.com, kevin.tian@intel.com,
	yi.l.liu@intel.com, ardb@kernel.org, akpm@linux-foundation.org,
	andreyknvl@gmail.com, wangjinchao@xfusion.com, gshan@redhat.com,
	ricarkol@google.com, linux-mm@kvack.org, lpieralisi@kernel.org,
	rananta@google.com, ryan.roberts@arm.com, aniketa@nvidia.com,
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	vsethi@nvidia.com, acurrid@nvidia.com, apopple@nvidia.com,
	jhubbard@nvidia.com, danw@nvidia.com, kvmarm@lists.linux.dev,
	mochs@nvidia.com, zhiw@nvidia.com, kvm@vger.kernel.org,
	linux-kernel@vger.kernel.org,
	linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH v6 1/4] kvm: arm64: introduce new flag for non-cacheable IO memory
Date: Thu, 8 Feb 2024 13:19:39 +0000	[thread overview]
Message-ID: <20240208131938.GB23428@willie-the-truck> (raw)
In-Reply-To: <20240207204652.22954-2-ankita@nvidia.com>

On Thu, Feb 08, 2024 at 02:16:49AM +0530, ankita@nvidia.com wrote:
> diff --git a/arch/arm64/kvm/hyp/pgtable.c b/arch/arm64/kvm/hyp/pgtable.c
> index c651df904fe3..2a893724ee9b 100644
> --- a/arch/arm64/kvm/hyp/pgtable.c
> +++ b/arch/arm64/kvm/hyp/pgtable.c
> @@ -717,15 +717,28 @@ void kvm_tlb_flush_vmid_range(struct kvm_s2_mmu *mmu,
>  static int stage2_set_prot_attr(struct kvm_pgtable *pgt, enum kvm_pgtable_prot prot,
>  				kvm_pte_t *ptep)
>  {
> -	bool device = prot & KVM_PGTABLE_PROT_DEVICE;
> -	kvm_pte_t attr = device ? KVM_S2_MEMATTR(pgt, DEVICE_nGnRE) :
> -			    KVM_S2_MEMATTR(pgt, NORMAL);
> +	kvm_pte_t attr;
>  	u32 sh = KVM_PTE_LEAF_ATTR_LO_S2_SH_IS;
>  
> +	switch (prot & (KVM_PGTABLE_PROT_DEVICE |
> +			KVM_PGTABLE_PROT_NORMAL_NC)) {
> +	case 0:
> +		attr = KVM_S2_MEMATTR(pgt, NORMAL);
> +		break;
> +	case KVM_PGTABLE_PROT_DEVICE:
> +		if (prot & KVM_PGTABLE_PROT_X)
> +			return -EINVAL;
> +		attr = KVM_S2_MEMATTR(pgt, DEVICE_nGnRE);
> +		break;
> +	case KVM_PGTABLE_PROT_NORMAL_NC:
> +		attr = KVM_S2_MEMATTR(pgt, NORMAL_NC);
> +		break;
> +	default:
> +		WARN_ON_ONCE(1);
> +	}

Cosmetic nit, but I'd find this a little easier to read if the normal
case was the default (i.e. drop 'case 0') and we returned an error for
DEVICE | NC.

Will