linux-kernel - Re: [PATCH v2] x86/kvm: Disable KVM_ASYNC_PF_SEND

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Date:   Wed, 8 Apr 2020 11:32:35 +0200
From:   Borislav Petkov <bp@...en8.de>
To:     Andy Lutomirski <luto@...capital.net>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Vivek Goyal <vgoyal@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Andy Lutomirski <luto@...nel.org>,
        Paolo Bonzini <pbonzini@...hat.com>,
        LKML <linux-kernel@...r.kernel.org>, X86 ML <x86@...nel.org>,
        kvm list <kvm@...r.kernel.org>, stable <stable@...r.kernel.org>
Subject: Re: [PATCH v2] x86/kvm: Disable KVM_ASYNC_PF_SEND_ALWAYS

On Tue, Apr 07, 2020 at 09:48:02PM -0700, Andy Lutomirski wrote:
> I’m fine with the flow being different. do_machine_check() could
> have entirely different logic to decide the error in PV.

Nope, do_machine_check() is already as ugly as it gets. I don't want any
more crap in it.

> But I think we should reuse the overall flow: kernel gets #MC with
> RIP pointing to the offending instruction. If there’s an extable
> entry that can handle memory failure, handle it. If it’s a user
> access, handle it. If it’s an unrecoverable error because it was a
> non-extable kernel access, oops or panic.
>
> The actual PV part could be extremely simple: the host just needs to
> tell the guest “this #MC is due to memory failure at this guest
> physical address”. No banks, no DIMM slot, no rendezvous crap
> (LMCE), no other nonsense. It would be nifty if the host also told the
> guest what the guest virtual address was if the host knows it.

It better be a whole different path and a whole different vector. If you
wanna keep it simple and apart from all of the other nonsense, then you
can just as well use a completely different vector.

Thx.

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette