linux-kernel - Re: [PATCH] kvm, x86: Properly check whether a pfn is an MMIO or not

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Date:   Thu, 15 Sep 2016 16:04:18 +0000
From:   "Kani, Toshimitsu" <toshi.kani@....com>
To:     "pbonzini@...hat.com" <pbonzini@...hat.com>,
        "karahmed@...zon.de" <karahmed@...zon.de>
CC:     "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "bp@...e.de" <bp@...e.de>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "x86@...nel.org" <x86@...nel.org>,
        "akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
        "hpa@...or.com" <hpa@...or.com>,
        "mingo@...hat.com" <mingo@...hat.com>,
        "tony.luck@...el.com" <tony.luck@...el.com>,
        "dvlasenk@...hat.com" <dvlasenk@...hat.com>,
        "rkrcmar@...hat.com" <rkrcmar@...hat.com>
Subject: Re: [PATCH] kvm, x86: Properly check whether a pfn is an MMIO or not

On Thu, 2016-09-15 at 08:22 +0200, Paolo Bonzini wrote:
> 
> On 15/09/2016 07:54, Raslan, KarimAllah wrote:
> > 
> > 
> > > 
> > > On Jun 22, 2016, at 3:41 PM, Paolo Bonzini <pbonzini@...hat.com>
> > > wrote:
> > > 
> > > 
> > > 
> > > On 22/06/2016 04:34, KarimAllah Ahmed wrote:
> > > > 
> > > > pfn_valid check is not sufficient because it only checks if a
> > > > page has a struct page or not, if for example "mem=" was passed
> > > > to the kernel some valid pages won't have a struct page. This
> > > > means that if guests were assigned valid memory that lies after
> > > > the mem= boundary it will be passed uncached to the guest no
> > > > matter what the guest caching attributes are for this memory.
> > > 
> > > How can you pass memory after the mem= boundary to the guest?
> > 
> > Does my previous reply answer your question?
> 
> Yes, but I'm not sure it's the right way to do it.  Looking at the
> e820 memory map seems pretty hacky.

Can you use region_intersects() for this check?  See memremap() as an
example using this interface.

-Toshi