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Date: Sun, 6 Jul 2025 19:52:50 -0500
From: Catalin Marinas <catalin.marinas@arm.com>
To: ankita@nvidia.com
Cc: jgg@nvidia.com, maz@kernel.org, oliver.upton@linux.dev,
	joey.gouly@arm.com, suzuki.poulose@arm.com, yuzenghui@huawei.com,
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	kvmarm@lists.linux.dev, linux-kernel@vger.kernel.org,
	linux-arm-kernel@lists.infradead.org, maobibo@loongson.cn
Subject: Re: [PATCH v10 2/6] KVM: arm64: Update the check to detect device
 memory
Message-ID: <aGsaYlZXvpU0Cngg@arm.com>
References: <20250705071717.5062-1-ankita@nvidia.com>
 <20250705071717.5062-3-ankita@nvidia.com>
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In-Reply-To: <20250705071717.5062-3-ankita@nvidia.com>

On Sat, Jul 05, 2025 at 07:17:13AM +0000, ankita@nvidia.com wrote:
> From: Ankit Agrawal <ankita@nvidia.com>
> 
> Currently, the kvm_is_device_pfn() detects if the memory is kernel
> mapped through pfn_is_map_memory. It thus implies whether KVM can
> use Cache Maintenance Operations (CMOs) on that PFN. It is a bit
> of a misnomer as it does not necessarily detect whether a PFN
> is for a device memory. Moreover, the function is only used at
> one place.
> 
> It would be better to directly call pfn_is_map_memory. Moreover
> we should restrict this call to VM_PFNMAP or VM_MIXEDMAP. Non PFMAP
> or MIXEDMAP VMA's must always contain normal pages which are
> struct page backed, have KVA's and are cachable. So we should always
> be able to go from phys to KVA to do a CMO.
> 
> Suggested-by: Jason Gunthorpe <jgg@nvidia.com>
> Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>
> Reviewed-by: David Hildenbrand <david@redhat.com>
> Tested-by: Donald Dutile <ddutile@redhat.com>
> Signed-off-by: Ankit Agrawal <ankita@nvidia.com>

Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>