Re: [PATCH v4 2/2] arm64: kvm: Introduce MTE VCPU feature

[Catalin Marinas]

Hi Steven,

On Mon, Oct 26, 2020 at 03:57:27PM +0000, Steven Price wrote:
> diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c
> index 19aacc7d64de..38fe25310ca1 100644
> --- a/arch/arm64/kvm/mmu.c
> +++ b/arch/arm64/kvm/mmu.c
> @@ -862,6 +862,26 @@ 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);
> +
> +     /*
> +      * The otherwise redundant test for system_supports_mte() allows the
> +      * code to be compiled out when CONFIG_ARM64_MTE is not present.
> +      */
> +     if (system_supports_mte() && kvm->arch.mte_enabled && pfn_valid(pfn)) {
> +             /*
> +              * VM will be able to see the page's tags, so we must ensure
> +              * they have been initialised.
> +              */
> +             struct page *page = pfn_to_page(pfn);
> +             long i, nr_pages = compound_nr(page);
> +
> +             /* if PG_mte_tagged is set, tags have already been initialised 
> */
> +             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 this page was swapped out and mapped back in, where does the
restoring from swap happen?

I may have asked in the past, is user_mem_abort() the only path for
mapping Normal pages into stage 2?

-- 
Catalin