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

[Steven Price]

On 17/11/2020 16:07, Catalin Marinas wrote:
> 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?

Restoring from swap happens above this in the call to gfn_to_pfn_prot()

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

That is my understanding (and yes you asked before) and no one has 
corrected me! ;)

Steve