linux-kernel - Re: [PATCH 1/2] KVM: MMU: Do not treat ZONE

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Message-ID: <20191106174652.GE16249@linux.intel.com>
Date:   Wed, 6 Nov 2019 09:46:52 -0800
From:   Sean Christopherson <sean.j.christopherson@...el.com>
To:     Paolo Bonzini <pbonzini@...hat.com>
Cc:     Radim Krčmář <rkrcmar@...hat.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org, Adam Borowski <kilobyte@...band.pl>,
        David Hildenbrand <david@...hat.com>,
        Dan Williams <dan.j.williams@...el.com>
Subject: Re: [PATCH 1/2] KVM: MMU: Do not treat ZONE_DEVICE pages as being
 reserved

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.