Re: [PATCH 1/2] KVM: MMU: Do not treat ZONE_DEVICE pages as being reserved

From: Sean Christopherson <sean.j.christopherson@intel.com>
To: Paolo Bonzini <pbonzini@redhat.com>
Cc: "Radim Krčmář" <rkrcmar@redhat.com>,
	"Vitaly Kuznetsov" <vkuznets@redhat.com>,
	"Wanpeng Li" <wanpengli@tencent.com>,
	"Jim Mattson" <jmattson@google.com>,
	"Joerg Roedel" <joro@8bytes.org>,
	kvm@vger.kernel.org, linux-kernel@vger.kernel.org,
	"Adam Borowski" <kilobyte@angband.pl>,
	"David Hildenbrand" <david@redhat.com>,
	"Dan Williams" <dan.j.williams@intel.com>
Subject: Re: [PATCH 1/2] KVM: MMU: Do not treat ZONE_DEVICE pages as being reserved
Date: Wed, 6 Nov 2019 09:46:52 -0800	[thread overview]
Message-ID: <20191106174652.GE16249@linux.intel.com> (raw)
In-Reply-To: <8ba98630-9ca0-85c2-3c94-45d54a448fca@redhat.com>

On Wed, Nov 06, 2019 at 06:14:40PM +0100, Paolo Bonzini wrote:
> On 06/11/19 18:07, Sean Christopherson wrote:
> >  void kvm_get_pfn(kvm_pfn_t pfn)
> >  {
> > -	if (!kvm_is_reserved_pfn(pfn))
> > +	if (!kvm_is_reserved_pfn(pfn) && !WARN_ON(kvm_is_zone_device_pfn(pfn)))
> >  		get_page(pfn_to_page(pfn));
> >  }
> >  EXPORT_SYMBOL_GPL(kvm_get_pfn);
> 
> Can you call remap_pfn_range with a source address that is ZONE_DEVICE?
>  If so, you would get a WARN from the kvm_get_pfn call in
> hva_to_pfn_remapped.

I don't know, at a quick glance I'm guessing it's possible via /dev/mem?
But, get_page() isn't sufficient to properly grab a ZONE_DEVICE page, so
the WARN is a good thing and intentional.

So assuming the answer is "yes", perhaps hva_to_pfn_remapped() should
adds its own check on kvm_is_zone_device_pfn() and return -EINVAL or
something?  That'd likely end up kill the guest, but wouldn't break the
kernel.