Re: [RFCv2 14/16] KVM: Handle protected memory in __kvm_map_gfn()/__kvm_unmap_gfn()

[Kirill A. Shutemov]

On Wed, Oct 21, 2020 at 06:50:28PM +0000, Edgecombe, Rick P wrote:
> On Tue, 2020-10-20 at 09:18 +0300, Kirill A. Shutemov wrote:
> > @@ -467,7 +477,7 @@ void iounmap(volatile void __iomem *addr)
> >  	p = find_vm_area((void __force *)addr);
> >  
> >  	if (!p) {
> > -		printk(KERN_ERR "iounmap: bad address %p\n", addr);
> > +		printk(KERN_ERR "iounmap: bad address %px\n", addr);
> 
> Unintentional?

Yep. Will fix.

> > @@ -2162,15 +2178,20 @@ static int __kvm_map_gfn(struct kvm_memslots
> > *slots, gfn_t gfn,
> >  			kvm_cache_gfn_to_pfn(slot, gfn, cache, gen);
> >  		}
> >  		pfn = cache->pfn;
> > +		protected = cache->protected;
> >  	} else {
> >  		if (atomic)
> >  			return -EAGAIN;
> > -		pfn = gfn_to_pfn_memslot(slot, gfn);
> > +		pfn = gfn_to_pfn_memslot_protected(slot, gfn,
> > &protected);
> >  	}
> >  	if (is_error_noslot_pfn(pfn))
> >  		return -EINVAL;
> >  
> > -	if (pfn_valid(pfn)) {
> > +	if (protected) {
> > +		if (atomic)
> > +			return -EAGAIN;
> > +		hva = ioremap_cache_force(pfn_to_hpa(pfn), PAGE_SIZE);
> > +	} else if (pfn_valid(pfn)) {
> >  		page = pfn_to_page(pfn);
> >  		if (atomic)
> >  			hva = kmap_atomic(page);
> 
> I think the page could have got unmapped since the gup via the
> hypercall on another CPU. It could be an avenue for the guest to crash
> the host.

Hm.. I'm not sure I follow. Could you elaborate on what scenario you have
in mind?

-- 
 Kirill A. Shutemov