linux-kernel - Re: [PATCH] vfio/type1: check pfn valid before converting to struct page

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Message-ID: <ZGbQF57Jl+me7Gpy@yzhao56-desk.sh.intel.com>
Date:   Fri, 19 May 2023 09:25:43 +0800
From:   Yan Zhao <yan.y.zhao@...el.com>
To:     Sean Christopherson <seanjc@...gle.com>
CC:     <kvm@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <alex.williamson@...hat.com>, <kevin.tian@...el.com>,
        <jgg@...dia.com>
Subject: Re: [PATCH] vfio/type1: check pfn valid before converting to struct
 page

On Thu, May 18, 2023 at 11:07:09AM -0700, Sean Christopherson wrote:
> On Thu, May 18, 2023, Yan Zhao wrote:
> > On Wed, May 17, 2023 at 08:19:04AM -0700, Sean Christopherson wrote:
> > > On Tue, May 16, 2023, Yan Zhao wrote:
> > > > vfio_pin_page_external() can return a phys_pfn for vma with VM_PFNMAP,
> > > > e.g. for MMIO PFNs.
> > > > 
> > > > It's necessary to check if it's a valid pfn before calling pfn_to_page().
> > > > 
> > > > Fixes: 34a255e67615 ("vfio: Replace phys_pfn with pages for vfio_pin_pages()")
> > > 
> > > Might be worth adding a blurb to call out that this is _not_ ABI breakage.  Prior
> > Do you mean "_not_ ABI breakage" with
> > 34a255e67615 ("vfio: Replace phys_pfn with pages for vfio_pin_pages()")
> > or with this fix commit?
> 
> Mostly the former.  I brought it up because _if_ there was breakage in that commit,
> then this fix would be "wrong" in the sense that it wouldn't undo any breakage, and
> would likely make it harder to restore the previous behavior.

Ok. Let me post v2 to describe the problem and background clearly.

Thanks!