Re: [PATCH v9 2/6] KVM: arm64: Update the check to detect device memory

David Hildenbrand
2025-07-04T14:18:47Z

On 21.06.25 06:21, 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. Otherwise
> the VMA has struct pages in it and mapped in the kernel VA.
>
> Suggested-by: Jason Gunthorpe <jgg@nvidia.com>
> Signed-off-by: Ankit Agrawal <ankita@nvidia.com>
> ---
> arch/arm64/kvm/mmu.c | 10 ++++------
> 1 file changed, 4 insertions(+), 6 deletions(-)
>
> diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c
> index 1601ab9527d4..5fe24f30999d 100644
> --- a/arch/arm64/kvm/mmu.c
> +++ b/arch/arm64/kvm/mmu.c
> @@ -193,11 +193,6 @@ int kvm_arch_flush_remote_tlbs_range(struct kvm *kvm,
> return 0;
> }
>
> -static bool kvm_is_device_pfn(unsigned long pfn)
> -{
> - return !pfn_is_map_memory(pfn);
> -}
> -
> static void *stage2_memcache_zalloc_page(void *arg)
> {
> struct kvm_mmu_memory_cache *mc = arg;
> @@ -1492,6 +1487,7 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
> enum kvm_pgtable_prot prot = KVM_PGTABLE_PROT_R;
> struct kvm_pgtable *pgt;
> struct page *page;
> + vm_flags_t vm_flags;
> enum kvm_pgtable_walk_flags flags = KVM_PGTABLE_WALK_HANDLE_FAULT | KVM_PGTABLE_WALK_SHARED;
>
> if (fault_is_perm)
> @@ -1619,6 +1615,8 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
>
> vfio_allow_any_uc = vma->vm_flags & VM_ALLOW_ANY_UNCACHED;
>
> + vm_flags = vma->vm_flags;
> +
> /* Don't use the VMA after the unlock -- it may have vanished */
> vma = NULL;
>
> @@ -1642,7 +1640,7 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
> if (is_error_noslot_pfn(pfn))
> return -EFAULT;
>
> - if (kvm_is_device_pfn(pfn)) {
> + if (vm_flags & (VM_PFNMAP | VM_MIXEDMAP) && !pfn_is_map_memory(pfn)) {

Reviewed-by: David Hildenbrand <david@redhat.com>

--
Cheers,

David / dhildenb