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

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Message-ID: <2ca7f677-723e-b96d-64aa-e2d858df7930@redhat.com>
Date:   Thu, 15 Sep 2016 18:22:41 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     "Kani, Toshimitsu" <toshi.kani@....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 15/09/2016 18:04, Kani, Toshimitsu wrote:
> 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.

This one seems more generic but very slow.

Paolo