linux-kernel - Re: [RFC KVM 24/27] kvm/isolation: KVM page fault handler

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Message-Id: <8DBEACE9-AB4C-4891-8522-A474CA59E325@amacapital.net>
Date:   Tue, 14 May 2019 08:43:44 -0700
From:   Andy Lutomirski <luto@...capital.net>
To:     Alexandre Chartre <alexandre.chartre@...cle.com>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Andy Lutomirski <luto@...nel.org>,
        Liran Alon <liran.alon@...cle.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Radim Krcmar <rkrcmar@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        kvm list <kvm@...r.kernel.org>, X86 ML <x86@...nel.org>,
        Linux-MM <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
        jan.setjeeilers@...cle.com, Jonathan Adams <jwadams@...gle.com>
Subject: Re: [RFC KVM 24/27] kvm/isolation: KVM page fault handler



> On May 14, 2019, at 8:36 AM, Alexandre Chartre <alexandre.chartre@...cle.com> wrote:
> 
> 
>> On 5/14/19 9:21 AM, Peter Zijlstra wrote:
>>> On Mon, May 13, 2019 at 07:02:30PM -0700, Andy Lutomirski wrote:
>>> This sounds like a great use case for static_call().  PeterZ, do you
>>> suppose we could wire up static_call() with the module infrastructure
>>> to make it easy to do "static_call to such-and-such GPL module symbol
>>> if that symbol is in a loaded module, else nop"?
>> You're basically asking it to do dynamic linking. And I suppose that is
>> technically possible.
>> However, I'm really starting to think kvm (or at least these parts of it
>> that want to play these games) had better not be a module anymore.
> 
> Maybe we can use an atomic notifier (e.g. page_fault_notifier)?
> 
> 

IMO that’s worse. I want to be able to read do_page_fault() and understand what happens and in what order.

Having do_page_fault run with the wrong CR3 is so fundamental to its operation that it needs to be very obvious what’s happening.