[v2,20/27] KVM: x86/mmu: Use page-track notifiers iff there are external users
Commit Message
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@google.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(-)
Comments
Nit: there is a typo in the commit header: "iff" -> "if"
> -void kvm_page_track_write(struct kvm_vcpu *vcpu, gpa_t gpa, const u8 *new,
> - int bytes)
> +void __kvm_page_track_write(struct kvm *kvm, gpa_t gpa, const u8 *new, int bytes)
Line length is 81 characters. A little longer than 80 :)
> +static inline bool kvm_page_track_has_external_user(struct kvm *kvm) { return false; }
This line is also too long.
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@google.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.
> @@ -55,6 +55,7 @@ void kvm_slot_page_track_remove_page(struct kvm *kvm,
> struct kvm_memory_slot *slot, gfn_t gfn,
> enum kvm_page_track_mode mode);
>
> +#ifdef CONFIG_KVM_EXTERNAL_WRITE_TRACKING
> enum pg_level kvm_page_track_max_mapping_level(struct kvm *kvm, gfn_t gfn,
> enum pg_level max_level);
>
> @@ -64,5 +65,6 @@ kvm_page_track_register_notifier(struct kvm *kvm,
> void
> kvm_page_track_unregister_notifier(struct kvm *kvm,
> struct kvm_page_track_notifier_node *n);
> +#endif /* CONFIG_KVM_EXTERNAL_WRITE_TRACKING */
>
> #endif
On Wed, Mar 15, 2023, Yan Zhao wrote:
> Nit: there is a typo in the commit header: "iff" -> "if"
>
> > -void kvm_page_track_write(struct kvm_vcpu *vcpu, gpa_t gpa, const u8 *new,
> > - int bytes)
> > +void __kvm_page_track_write(struct kvm *kvm, gpa_t gpa, const u8 *new, int bytes)
> Line length is 81 characters. A little longer than 80 :)
>
> > +static inline bool kvm_page_track_has_external_user(struct kvm *kvm) { return false; }
> This line is also too long.
The 80 character limit is a "soft" limit these days, e.g. checkpatch only complains
if a line is 100+. In KVM x86, the preferred style is to treat the 80 char limit
as "firm", for lack of a better word. E.g. let a line run over if it's just a
char or two and there's no other wrapping in the declaration, but don't create long
lines just because checkpatch no longer yells.
There's obviously a fair bit of subjectivity, but the guideline has worked well
so far (hopefully I didn't just jinx us).
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@google.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.
Thanks yet again!
On Wed, Mar 15, 2023 at 09:21:34AM -0700, Sean Christopherson wrote:
> On Wed, Mar 15, 2023, Yan Zhao wrote:
> > Nit: there is a typo in the commit header: "iff" -> "if"
> >
> > > -void kvm_page_track_write(struct kvm_vcpu *vcpu, gpa_t gpa, const u8 *new,
> > > - int bytes)
> > > +void __kvm_page_track_write(struct kvm *kvm, gpa_t gpa, const u8 *new, int bytes)
> > Line length is 81 characters. A little longer than 80 :)
> >
> > > +static inline bool kvm_page_track_has_external_user(struct kvm *kvm) { return false; }
> > This line is also too long.
>
> The 80 character limit is a "soft" limit these days, e.g. checkpatch only complains
> if a line is 100+. In KVM x86, the preferred style is to treat the 80 char limit
> as "firm", for lack of a better word. E.g. let a line run over if it's just a
> char or two and there's no other wrapping in the declaration, but don't create long
> lines just because checkpatch no longer yells.
>
Got it. It's helpful to me!
> There's obviously a fair bit of subjectivity, but the guideline has worked well
> so far (hopefully I didn't just jinx us).
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@google.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
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@google.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 :)
@@ -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
@@ -55,6 +55,7 @@ void kvm_slot_page_track_remove_page(struct kvm *kvm,
struct kvm_memory_slot *slot, gfn_t gfn,
enum kvm_page_track_mode mode);
+#ifdef CONFIG_KVM_EXTERNAL_WRITE_TRACKING
enum pg_level kvm_page_track_max_mapping_level(struct kvm *kvm, gfn_t gfn,
enum pg_level max_level);
@@ -64,5 +65,6 @@ kvm_page_track_register_notifier(struct kvm *kvm,
void
kvm_page_track_unregister_notifier(struct kvm *kvm,
struct kvm_page_track_notifier_node *n);
+#endif /* CONFIG_KVM_EXTERNAL_WRITE_TRACKING */
#endif
@@ -194,6 +194,7 @@ bool kvm_slot_page_track_is_active(struct kvm *kvm,
return !!READ_ONCE(slot->arch.gfn_track[mode][index]);
}
+#ifdef CONFIG_KVM_EXTERNAL_WRITE_TRACKING
void kvm_page_track_cleanup(struct kvm *kvm)
{
struct kvm_page_track_notifier_head *head;
@@ -255,14 +256,13 @@ EXPORT_SYMBOL_GPL(kvm_page_track_unregister_notifier);
* The node should figure out if the written page is the one that node is
* interested in by itself.
*/
-void kvm_page_track_write(struct kvm_vcpu *vcpu, gpa_t gpa, const u8 *new,
- int bytes)
+void __kvm_page_track_write(struct kvm *kvm, gpa_t gpa, const u8 *new, int bytes)
{
struct kvm_page_track_notifier_head *head;
struct kvm_page_track_notifier_node *n;
int idx;
- head = &vcpu->kvm->arch.track_notifier_head;
+ head = &kvm->arch.track_notifier_head;
if (hlist_empty(&head->track_notifier_list))
return;
@@ -273,8 +273,6 @@ void kvm_page_track_write(struct kvm_vcpu *vcpu, gpa_t gpa, const u8 *new,
if (n->track_write)
n->track_write(gpa, new, bytes, n);
srcu_read_unlock(&head->track_srcu, idx);
-
- kvm_mmu_track_write(vcpu, gpa, new, bytes);
}
/*
@@ -317,3 +315,4 @@ enum pg_level kvm_page_track_max_mapping_level(struct kvm *kvm, gfn_t gfn,
return max_level;
}
EXPORT_SYMBOL_GPL(kvm_page_track_max_mapping_level);
+#endif
@@ -6,8 +6,6 @@
#include <asm/kvm_page_track.h>
-int kvm_page_track_init(struct kvm *kvm);
-void kvm_page_track_cleanup(struct kvm *kvm);
bool kvm_page_track_write_tracking_enabled(struct kvm *kvm);
int kvm_page_track_write_tracking_alloc(struct kvm_memory_slot *slot);
@@ -21,13 +19,36 @@ bool kvm_slot_page_track_is_active(struct kvm *kvm,
const struct kvm_memory_slot *slot,
gfn_t gfn, enum kvm_page_track_mode mode);
-void kvm_page_track_write(struct kvm_vcpu *vcpu, gpa_t gpa, const u8 *new,
- int bytes);
+#ifdef CONFIG_KVM_EXTERNAL_WRITE_TRACKING
+int kvm_page_track_init(struct kvm *kvm);
+void kvm_page_track_cleanup(struct kvm *kvm);
+
+void __kvm_page_track_write(struct kvm *kvm, gpa_t gpa, const u8 *new, int bytes);
void kvm_page_track_delete_slot(struct kvm *kvm, struct kvm_memory_slot *slot);
static inline bool kvm_page_track_has_external_user(struct kvm *kvm)
{
return hlist_empty(&kvm->arch.track_notifier_head.track_notifier_list);
}
+#else
+static inline int kvm_page_track_init(struct kvm *kvm) { return 0; }
+static inline void kvm_page_track_cleanup(struct kvm *kvm) { }
+
+static inline void __kvm_page_track_write(struct kvm *kvm, gpa_t gpa,
+ const u8 *new, int bytes) { }
+static inline void kvm_page_track_delete_slot(struct kvm *kvm,
+ struct kvm_memory_slot *slot) { }
+
+static inline bool kvm_page_track_has_external_user(struct kvm *kvm) { return false; }
+
+#endif /* CONFIG_KVM_EXTERNAL_WRITE_TRACKING */
+
+static inline void kvm_page_track_write(struct kvm_vcpu *vcpu, gpa_t gpa,
+ const u8 *new, int bytes)
+{
+ __kvm_page_track_write(vcpu->kvm, gpa, new, bytes);
+
+ kvm_mmu_track_write(vcpu, gpa, new, bytes);
+}
#endif /* __KVM_X86_PAGE_TRACK_H */