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

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Date: Thu, 8 Feb 2024 13:19:39 +0000
From: Will Deacon <will@...nel.org>
To: ankita@...dia.com
Cc: jgg@...dia.com, maz@...nel.org, oliver.upton@...ux.dev,
	james.morse@....com, suzuki.poulose@....com, yuzenghui@...wei.com,
	reinette.chatre@...el.com, surenb@...gle.com, stefanha@...hat.com,
	brauner@...nel.org, catalin.marinas@....com, mark.rutland@....com,
	alex.williamson@...hat.com, kevin.tian@...el.com,
	yi.l.liu@...el.com, ardb@...nel.org, akpm@...ux-foundation.org,
	andreyknvl@...il.com, wangjinchao@...sion.com, gshan@...hat.com,
	ricarkol@...gle.com, linux-mm@...ck.org, lpieralisi@...nel.org,
	rananta@...gle.com, ryan.roberts@....com, aniketa@...dia.com,
	cjia@...dia.com, kwankhede@...dia.com, targupta@...dia.com,
	vsethi@...dia.com, acurrid@...dia.com, apopple@...dia.com,
	jhubbard@...dia.com, danw@...dia.com, kvmarm@...ts.linux.dev,
	mochs@...dia.com, zhiw@...dia.com, kvm@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v6 1/4] kvm: arm64: introduce new flag for non-cacheable
 IO memory

On Thu, Feb 08, 2024 at 02:16:49AM +0530, ankita@...dia.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