Re: [PATCH v10 2/6] arm64: kvm: Introduce MTE VM feature

[Catalin Marinas <catalin.marinas@arm.com>]

On Fri, Mar 12, 2021 at 03:18:58PM +0000, Steven Price wrote:
> diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c
> index 77cb2d28f2a4..b31b7a821f90 100644
> --- a/arch/arm64/kvm/mmu.c
> +++ b/arch/arm64/kvm/mmu.c
> @@ -879,6 +879,22 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
>  	if (vma_pagesize == PAGE_SIZE && !force_pte)
>  		vma_pagesize = transparent_hugepage_adjust(memslot, hva,
>  							   &pfn, &fault_ipa);
> +
> +	if (fault_status != FSC_PERM && kvm_has_mte(kvm) && pfn_valid(pfn)) {

This pfn_valid() check may be problematic. Following commit eeb0753ba27b
("arm64/mm: Fix pfn_valid() for ZONE_DEVICE based memory"), it returns
true for ZONE_DEVICE memory but such memory is allowed not to support
MTE.

I now wonder if we can get a MAP_ANONYMOUS mapping of ZONE_DEVICE pfn
even without virtualisation.

> +		/*
> +		 * VM will be able to see the page's tags, so we must ensure
> +		 * they have been initialised. if PG_mte_tagged is set, tags
> +		 * have already been initialised.
> +		 */
> +		struct page *page = pfn_to_page(pfn);
> +		unsigned long i, nr_pages = vma_pagesize >> PAGE_SHIFT;
> +
> +		for (i = 0; i < nr_pages; i++, page++) {
> +			if (!test_and_set_bit(PG_mte_tagged, &page->flags))
> +				mte_clear_page_tags(page_address(page));
> +		}
> +	}
> +
>  	if (writable)
>  		prot |= KVM_PGTABLE_PROT_W;
>  

-- 
Catalin