linux-kernel - Re: [PATCH v6 16/17] RFC: kvm: pass kvm argument to follow

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Date:   Fri, 20 Nov 2020 16:44:59 +0100
From:   Daniel Vetter <daniel.vetter@...ll.ch>
To:     Paolo Bonzini <pbonzini@...hat.com>
Cc:     DRI Development <dri-devel@...ts.freedesktop.org>,
        LKML <linux-kernel@...r.kernel.org>,
        KVM list <kvm@...r.kernel.org>, Linux MM <linux-mm@...ck.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        linux-samsung-soc <linux-samsung-soc@...r.kernel.org>,
        "open list:DMA BUFFER SHARING FRAMEWORK" 
        <linux-media@...r.kernel.org>,
        Daniel Vetter <daniel.vetter@...el.com>,
        Christoph Hellwig <hch@...radead.org>,
        Jason Gunthorpe <jgg@...pe.ca>,
        Kees Cook <keescook@...omium.org>,
        Dan Williams <dan.j.williams@...el.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        John Hubbard <jhubbard@...dia.com>,
        Jérôme Glisse <jglisse@...hat.com>,
        Jan Kara <jack@...e.cz>
Subject: Re: [PATCH v6 16/17] RFC: kvm: pass kvm argument to follow_pfn callsites

On Fri, Nov 20, 2020 at 4:33 PM Paolo Bonzini <pbonzini@...hat.com> wrote:
>
> On 19/11/20 15:41, Daniel Vetter wrote:
> > Both Christoph Hellwig and Jason Gunthorpe suggested that usage of
> > follow_pfn by modules should be locked down more. To do so callers
> > need to be able to pass the mmu_notifier subscription corresponding
> > to the mm_struct to follow_pfn().
> >
> > This patch does the rote work of doing that in the kvm subsystem. In
> > most places this is solved by passing struct kvm * down the call
> > stacks as an additional parameter, since that contains the
> > mmu_notifier.
> >
> > Compile tested on all affected arch.
>
> It's a bit of a pity, it's making an API more complex (the point of
> gfn_to_pfn_memslot vs gfn_to_pfn is exactly that you don't need a
> "struct kvm*" and it's clear that you've already done the lookup into
> that struct kvm.

Yeah I noticed that, I think pushing the lookups down should work, but
that's a fairly large-scale change. I didn't want to do that for the
RFC since it would distract from the actual change/goal.
-Daniel

> But it's not a big deal, and the rationale at least makes sense.  So,
>
> Acked-by: Paolo Bonzini <pbonzini@...hat.com>
>
> Paolo



-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch