linux-kernel - Re: [PATCH v9 6/6] KVM: x86/mmu: Handle non-refcounted pages

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Message-ID: <CAD=HUj62vdy9CmqHWsAQi4S6i1ZH8uUE81p8Wu67pQd5vNRr+w@mail.gmail.com>
Date:   Tue, 19 Sep 2023 11:31:20 +0900
From:   David Stevens <stevensd@...omium.org>
To:     Dmitry Osipenko <dmitry.osipenko@...labora.com>
Cc:     Sean Christopherson <seanjc@...gle.com>,
        Yu Zhang <yu.c.zhang@...ux.intel.com>,
        Isaku Yamahata <isaku.yamahata@...il.com>,
        Zhi Wang <zhi.wang.linux@...il.com>, kvmarm@...ts.linux.dev,
        linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Subject: Re: [PATCH v9 6/6] KVM: x86/mmu: Handle non-refcounted pages

On Mon, Sep 18, 2023 at 6:58 PM Dmitry Osipenko
<dmitry.osipenko@...labora.com> wrote:
>
> On 9/11/23 05:16, David Stevens wrote:
> > From: David Stevens <stevensd@...omium.org>
> >
> > Handle non-refcounted pages in __kvm_faultin_pfn. This allows the host
> > to map memory into the guest that is backed by non-refcounted struct
> > pages - for example, the tail pages of higher order non-compound pages
> > allocated by the amdgpu driver via ttm_pool_alloc_page.
> >
> > The bulk of this change is tracking the is_refcounted_page flag so that
> > non-refcounted pages don't trigger page_count() == 0 warnings. This is
> > done by storing the flag in an unused bit in the sptes. There are no
> > bits available in PAE SPTEs, so non-refcounted pages can only be handled
> > on TDP and x86-64.
> >
> > Signed-off-by: David Stevens <stevensd@...omium.org>
> > ---
> >  arch/x86/kvm/mmu/mmu.c          | 52 +++++++++++++++++++++++----------
> >  arch/x86/kvm/mmu/mmu_internal.h |  1 +
> >  arch/x86/kvm/mmu/paging_tmpl.h  |  8 +++--
> >  arch/x86/kvm/mmu/spte.c         |  4 ++-
> >  arch/x86/kvm/mmu/spte.h         | 12 +++++++-
> >  arch/x86/kvm/mmu/tdp_mmu.c      | 22 ++++++++------
> >  include/linux/kvm_host.h        |  3 ++
> >  virt/kvm/kvm_main.c             |  6 ++--
> >  8 files changed, 76 insertions(+), 32 deletions(-)
>
> Could you please tell which kernel tree you used for the base of this
> series? This patch #6 doesn't apply cleanly to stable/mainline/next/kvm
>
> error: sha1 information is lacking or useless (arch/x86/kvm/mmu/mmu.c).
> error: could not build fake ancestor

This series is based on the kvm next branch (i.e.
https://git.kernel.org/pub/scm/virt/kvm/kvm.git/log/?h=next). The
specific hash is d011151616e73de20c139580b73fa4c7042bd861.

-David