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

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Message-ID: <cd56eb8a-fbec-e81f-9c14-d1256a193b68@redhat.com>
Date:   Fri, 20 Nov 2020 16:33:44 +0100
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Daniel Vetter <daniel.vetter@...ll.ch>,
        DRI Development <dri-devel@...ts.freedesktop.org>,
        LKML <linux-kernel@...r.kernel.org>
Cc:     kvm@...r.kernel.org, linux-mm@...ck.org,
        linux-arm-kernel@...ts.infradead.org,
        linux-samsung-soc@...r.kernel.org, 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 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.

But it's not a big deal, and the rationale at least makes sense.  So,

Acked-by: Paolo Bonzini <pbonzini@...hat.com>

Paolo