linux-kernel - Re: [PATCH v6 3/4] kvm: arm64: set io memory s2 pte as normalnc for vfio pci device

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Message-ID: <ZcTWnDBfAtMriXqp@linux.dev>
Date: Thu, 8 Feb 2024 13:26:52 +0000
From: Oliver Upton <oliver.upton@...ux.dev>
To: ankita@...dia.com
Cc: jgg@...dia.com, maz@...nel.org, james.morse@....com,
	suzuki.poulose@....com, yuzenghui@...wei.com,
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	linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v6 3/4] kvm: arm64: set io memory s2 pte as normalnc for
 vfio pci device

On Thu, Feb 08, 2024 at 02:16:51AM +0530, ankita@...dia.com wrote:
> @@ -1557,10 +1559,18 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
>  	if (exec_fault)
>  		prot |= KVM_PGTABLE_PROT_X;
>  
> -	if (device)
> -		prot |= KVM_PGTABLE_PROT_DEVICE;
> -	else if (cpus_have_final_cap(ARM64_HAS_CACHE_DIC))
> +	if (device) {
> +		/*
> +		 * To provide VM with the ability to get device IO memory
> +		 * with NormalNC property, map device MMIO as NormalNC in S2.
> +		 */

nit: the comment doesn't provide anything of value, the logic is rather
straightforward here.

> +		if (vfio_allow_wc)
> +			prot |= KVM_PGTABLE_PROT_NORMAL_NC;
> +		else
> +			prot |= KVM_PGTABLE_PROT_DEVICE;
> +	} else if (cpus_have_final_cap(ARM64_HAS_CACHE_DIC)) {
>  		prot |= KVM_PGTABLE_PROT_X;
> +	}
>  
>  	/*
>  	 * Under the premise of getting a FSC_PERM fault, we just need to relax
> -- 
> 2.34.1
>

-- 
Thanks,
Oliver