[PATCH v4 17/21] KVM: arm64: Convert user_mem_abort() to generic page-table API

[Will Deacon]

On Wed, Sep 09, 2020 at 06:12:29PM +0100, Marc Zyngier wrote:
> On 2020-09-09 15:20, Alexandru Elisei wrote:
> > On 9/7/20 4:23 PM, Will Deacon wrote:
> > > @@ -1610,62 +1605,31 @@ 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 (writable)
> > > +	if (writable) {
> > > +		prot |= KVM_PGTABLE_PROT_W;
> > >  		kvm_set_pfn_dirty(pfn);
> > > +		mark_page_dirty(kvm, gfn);
> > 
> > The previous code called mark_page_dirty() only if the vma_pagesize ==
> > PAGE_SIZE
> > (and writable was true, obviously). Is this supposed to fix a bug?
> 
> No, this is actually introducing one. mark_page_dirty() checks that there is
> an
> associated bitmap, and thus only happens when writing to a single page, but
> we
> shouldn't do it for R/O memslots, which the current code avoids. It should
> be
> guarded by logging_active.

gfn_to_pfn_prot() will set "writable" to false for R/O memslots, so I think
we're good here.

Will