linux-kernel - Re: [PATCH v2] x86/kvm: Handle async page faults directly through do_page

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Message-ID: <328119b6-38a3-8b74-9e89-629977316ff4@redhat.com>
Date:   Mon, 2 Mar 2020 11:41:20 +0100
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Nadav Amit <nadav.amit@...il.com>,
        Andy Lutomirski <luto@...nel.org>
Cc:     LKML <linux-kernel@...r.kernel.org>, x86 <x86@...nel.org>,
        kvm list <kvm@...r.kernel.org>
Subject: Re: [PATCH v2] x86/kvm: Handle async page faults directly through
 do_page_fault()

On 02/03/20 10:28, Nadav Amit wrote:
> 
> Yet, this might be a slippery slope, making Linux optimized to run on KVM
> (and maybe Xen). In other words, I wonder whether a similar change was
> acceptable for a paravirtual feature that is only supported by a proprietary
> hypervisor, such as Hyper-V or VMware.

Your concern is understandable.  I think in this case Andy's patch makes
sense since there is a hooking mechanism that is used in exactly one
case and there are no performance issues in removing it.  In fact if
more hypervisors implemented a #PF extension I would keep the static
branch, but use it to choose between a pvop and the default case; this
would be a much more localized change, so arguably better than trap_init.

Paolo