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

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Message-ID: <a063d76e-940c-5c68-bfca-fc0d99305411@redhat.com>
Date:   Thu, 15 Sep 2016 08:22:35 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     "Raslan, KarimAllah" <karahmed@...zon.de>
Cc:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "x86@...nel.org" <x86@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H . Peter Anvin" <hpa@...or.com>,
        Radim Krčmář <rkrcmar@...hat.com>,
        Borislav Petkov <bp@...e.de>,
        Denys Vlasenko <dvlasenk@...hat.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Toshi Kani <toshi.kani@....com>,
        Tony Luck <tony.luck@...el.com>
Subject: Re: [PATCH] kvm, x86: Properly check whether a pfn is an MMIO or not



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.

Paolo