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

[Catalin Marinas]

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