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From:   Andy Lutomirski <luto@kernel.org>
Date:   Mon, 13 May 2019 19:02:30 -0700
Message-ID: <CALCETrUcR=3nfOtFW2qt3zaa7CnNJWJLqRY8AS9FTJVHErjhfg@mail.gmail.com>
Subject: Re: [RFC KVM 24/27] kvm/isolation: KVM page fault handler
To:     Liran Alon <liran.alon@oracle.com>
Cc:     Peter Zijlstra <peterz@infradead.org>,
        Alexandre Chartre <alexandre.chartre@oracle.com>,
        Paolo Bonzini <pbonzini@redhat.com>,
        Radim Krcmar <rkrcmar@redhat.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
        "H. Peter Anvin" <hpa@zytor.com>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        Andrew Lutomirski <luto@kernel.org>,
        kvm list <kvm@vger.kernel.org>, X86 ML <x86@kernel.org>,
        Linux-MM <linux-mm@kvack.org>,
        LKML <linux-kernel@vger.kernel.org>,
        Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>,
        jan.setjeeilers@oracle.com, Jonathan Adams <jwadams@google.com>
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On Mon, May 13, 2019 at 2:26 PM Liran Alon <liran.alon@oracle.com> wrote:
>
>
>
> > On 13 May 2019, at 18:15, Peter Zijlstra <peterz@infradead.org> wrote:
> >
> > On Mon, May 13, 2019 at 04:38:32PM +0200, Alexandre Chartre wrote:
> >> diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c
> >> index 46df4c6..317e105 100644
> >> --- a/arch/x86/mm/fault.c
> >> +++ b/arch/x86/mm/fault.c
> >> @@ -33,6 +33,10 @@
> >> #define CREATE_TRACE_POINTS
> >> #include <asm/trace/exceptions.h>
> >>
> >> +bool (*kvm_page_fault_handler)(struct pt_regs *regs, unsigned long error_code,
> >> +                           unsigned long address);
> >> +EXPORT_SYMBOL(kvm_page_fault_handler);
> >
> > NAK NAK NAK NAK
> >
> > This is one of the biggest anti-patterns around.
>
> I agree.
> I think that mm should expose a mm_set_kvm_page_fault_handler() or something (give it a better name).
> Similar to how arch/x86/kernel/irq.c have kvm_set_posted_intr_wakeup_handler().
>
> -Liran
>

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"?