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Message-ID: <ZFWopeCUzrQxBrUh@yzhao56-desk.sh.intel.com>
Date: Sat, 6 May 2023 09:08:53 +0800
From: Yan Zhao <yan.y.zhao@...el.com>
To: Sean Christopherson <seanjc@...gle.com>
CC: <kvm@...r.kernel.org>, <intel-gfx@...ts.freedesktop.org>,
<linux-kernel@...r.kernel.org>,
Zhenyu Wang <zhenyuw@...ux.intel.com>,
"Ben Gardon" <bgardon@...gle.com>,
Paolo Bonzini <pbonzini@...hat.com>,
<intel-gvt-dev@...ts.freedesktop.org>,
Zhi Wang <zhi.a.wang@...el.com>
Subject: Re: [PATCH v2 20/27] KVM: x86/mmu: Use page-track notifiers iff
there are external users
On Thu, May 04, 2023 at 12:54:40PM -0700, Sean Christopherson wrote:
> On Wed, Mar 15, 2023, Sean Christopherson wrote:
> > On Wed, Mar 15, 2023, Yan Zhao wrote:
> > > On Fri, Mar 10, 2023 at 04:22:51PM -0800, Sean Christopherson wrote:
> > > > Disable the page-track notifier code at compile time if there are no
> > > > external users, i.e. if CONFIG_KVM_EXTERNAL_WRITE_TRACKING=n. KVM itself
> > > > now hooks emulated writes directly instead of relying on the page-track
> > > > mechanism.
> > > >
> > > > Signed-off-by: Sean Christopherson <seanjc@...gle.com>
> > > > ---
> > > > arch/x86/include/asm/kvm_host.h | 2 ++
> > > > arch/x86/include/asm/kvm_page_track.h | 2 ++
> > > > arch/x86/kvm/mmu/page_track.c | 9 ++++-----
> > > > arch/x86/kvm/mmu/page_track.h | 29 +++++++++++++++++++++++----
> > > > 4 files changed, 33 insertions(+), 9 deletions(-)
> > > >
> > > > diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
> > > > index 1a4225237564..a3423711e403 100644
> > > > --- a/arch/x86/include/asm/kvm_host.h
> > > > +++ b/arch/x86/include/asm/kvm_host.h
> > > > @@ -1265,7 +1265,9 @@ struct kvm_arch {
> > > > * create an NX huge page (without hanging the guest).
> > > > */
> > > > struct list_head possible_nx_huge_pages;
> > > > +#ifdef CONFIG_KVM_EXTERNAL_WRITE_TRACKING
> > > > struct kvm_page_track_notifier_head track_notifier_head;
> > > > +#endif
> > > > /*
> > > > * Protects marking pages unsync during page faults, as TDP MMU page
> > > > * faults only take mmu_lock for read. For simplicity, the unsync
> > > > diff --git a/arch/x86/include/asm/kvm_page_track.h b/arch/x86/include/asm/kvm_page_track.h
> > > > index deece45936a5..53c2adb25a07 100644
> > > > --- a/arch/x86/include/asm/kvm_page_track.h
> > > > +++ b/arch/x86/include/asm/kvm_page_track.h
> > > The "#ifdef CONFIG_KVM_EXTERNAL_WRITE_TRACKING" can be moved to the
> > > front of this file?
> > > All the structures are only exposed for external users now.
> >
> > Huh. I've no idea why I didn't do that. IIRC, the entire reason past me wrapped
> > track_notifier_head in an #ifdef was to allow this change in kvm_page_track.h.
> >
> > I'll do this in the next version unless I discover an edge case I'm overlooking.
>
> Ah, deja vu. I tried this first time around, and got yelled at by the kernel test
> robot. Unsuprisingly, my second attempt yielded the same result :-)
>
> HDRTEST drivers/gpu/drm/i915/gvt/gvt.h
> In file included from <command-line>:
> gpu/drivers/gpu/drm/i915/gvt/gvt.h:236:45: error: field ‘track_node’ has incomplete type
> 236 | struct kvm_page_track_notifier_node track_node;
> | ^~~~~~~~~~
>
> The problem is direct header inclusion. Nothing in the kernel includes gvt.h
> when CONFIG_DRM_I915_GVT=n, but the header include guard tests include headers
> directly on the command line. I think I'll define a "stub" specifically to play
> nice with this sort of testing. Guarding the guts of gvt.h with CONFIG_DRM_I915_GVT
> would just propagate the problem, and guarding the node definition in "struct
> intel_vgpu" would be confusing since the guard would be dead code for all intents
> and purposes.
>
> The obvious alternative would be to leave kvm_page_track_notifier_node outside of
> the #ifdef, but I really want to bury kvm_page_track_notifier_head for KVM's sake,
> and having "head" buried but not "node" would also be weird and confusing.
>
> diff --git a/arch/x86/include/asm/kvm_page_track.h b/arch/x86/include/asm/kvm_page_track.h
> index 33f087437209..3d040741044b 100644
> --- a/arch/x86/include/asm/kvm_page_track.h
> +++ b/arch/x86/include/asm/kvm_page_track.h
> @@ -51,6 +51,12 @@ void kvm_page_track_unregister_notifier(struct kvm *kvm,
>
> int kvm_write_track_add_gfn(struct kvm *kvm, gfn_t gfn);
> int kvm_write_track_remove_gfn(struct kvm *kvm, gfn_t gfn);
> +#else
> +/*
> + * Allow defining a node in a structure even if page tracking is disabled, e.g.
> + * to play nice with testing headers via direct inclusion from the command line.
> + */
> +struct kvm_page_track_notifier_node {};
> #endif /* CONFIG_KVM_EXTERNAL_WRITE_TRACKING */
>
> #endif
>
Or check CONFIG_KVM_EXTERNAL_WRITE_TRACKING in gvt.h ?
e.g.
diff --git a/drivers/gpu/drm/i915/gvt/gvt.h b/drivers/gpu/drm/i915/gvt/gvt.h
index 53a0a42a50db..005cdc4fb66a 100644
--- a/drivers/gpu/drm/i915/gvt/gvt.h
+++ b/drivers/gpu/drm/i915/gvt/gvt.h
@@ -233,7 +233,9 @@ struct intel_vgpu {
unsigned long nr_cache_entries;
struct mutex cache_lock;
+#ifdef CONFIG_KVM_EXTERNAL_WRITE_TRACKING
struct kvm_page_track_notifier_node track_node;
+#endif
#define NR_BKT (1 << 18)
struct hlist_head ptable[NR_BKT];
#undef NR_BKT
The justification is that gvt.h can be include without kvmgt, e.g. xengt
previously.
But given currently there's no such case, I'm fine with both way :)
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