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

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Message-ID: <ZGZpTWnnbzAr+AwN@google.com>
Date:   Thu, 18 May 2023 11:07:09 -0700
From:   Sean Christopherson <seanjc@...gle.com>
To:     Yan Zhao <yan.y.zhao@...el.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, 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.