| Message ID | 1303984323-3203-3-git-send-email-gleb@redhat.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
Hi Gleb, Thats a neat idea. On Thu, Apr 28, 2011 at 12:52:03PM +0300, Gleb Natapov wrote: > KVM does not hold any references to rcu protected data when it switches > CPU into a guest mode. In fact switching to a guest mode is very similar > to exiting to userspase from rcu point of view. In addition CPU may stay > in a guest mode for quite a long time (up to one time slice). Lets treat > guest mode as quiescent state, just like we do with user-mode execution. > > Signed-off-by: Gleb Natapov <gleb@redhat.com> > --- > include/linux/kvm_host.h | 1 + > 1 files changed, 1 insertions(+), 0 deletions(-) > > diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h > index 0bc3d37..a347bce 100644 > --- a/include/linux/kvm_host.h > +++ b/include/linux/kvm_host.h > @@ -593,6 +593,7 @@ static inline void kvm_guest_enter(void) > { > account_system_vtime(current); > current->flags |= PF_VCPU; > + rcu_note_context_switch(smp_processor_id()); > } > > static inline void kvm_guest_exit(void) > -- > 1.7.2.3 Please have it in x86's vcpu_enter_guest, then its more explicit (uncertain about the context of kvm_guest_enter call in other arches). -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
On 05/03/2011 04:13 PM, Marcelo Tosatti wrote: > Please have it in x86's vcpu_enter_guest, then its more explicit > (uncertain about the context of kvm_guest_enter call in other arches). We do need it for other archs, don't we?
On Tue, May 03, 2011 at 10:13:17AM -0300, Marcelo Tosatti wrote: > Hi Gleb, > > Thats a neat idea. > > On Thu, Apr 28, 2011 at 12:52:03PM +0300, Gleb Natapov wrote: > > KVM does not hold any references to rcu protected data when it switches > > CPU into a guest mode. In fact switching to a guest mode is very similar > > to exiting to userspase from rcu point of view. In addition CPU may stay > > in a guest mode for quite a long time (up to one time slice). Lets treat > > guest mode as quiescent state, just like we do with user-mode execution. > > > > Signed-off-by: Gleb Natapov <gleb@redhat.com> > > --- > > include/linux/kvm_host.h | 1 + > > 1 files changed, 1 insertions(+), 0 deletions(-) > > > > diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h > > index 0bc3d37..a347bce 100644 > > --- a/include/linux/kvm_host.h > > +++ b/include/linux/kvm_host.h > > @@ -593,6 +593,7 @@ static inline void kvm_guest_enter(void) > > { > > account_system_vtime(current); > > current->flags |= PF_VCPU; > > + rcu_note_context_switch(smp_processor_id()); > > } > > > > static inline void kvm_guest_exit(void) > > -- > > 1.7.2.3 > > Please have it in x86's vcpu_enter_guest, then its more explicit > (uncertain about the context of kvm_guest_enter call in other arches). > I checked all of them and kvm_guest_enter() is always called with local irq disabled. Paul confirmed that rcu_note_context_switch() can be called in such context. -- Gleb. -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
On Tue, May 03, 2011 at 04:21:23PM +0300, Gleb Natapov wrote: > On Tue, May 03, 2011 at 10:13:17AM -0300, Marcelo Tosatti wrote: > > Hi Gleb, > > > > Thats a neat idea. > > > > On Thu, Apr 28, 2011 at 12:52:03PM +0300, Gleb Natapov wrote: > > > KVM does not hold any references to rcu protected data when it switches > > > CPU into a guest mode. In fact switching to a guest mode is very similar > > > to exiting to userspase from rcu point of view. In addition CPU may stay > > > in a guest mode for quite a long time (up to one time slice). Lets treat > > > guest mode as quiescent state, just like we do with user-mode execution. > > > > > > Signed-off-by: Gleb Natapov <gleb@redhat.com> > > > --- > > > include/linux/kvm_host.h | 1 + > > > 1 files changed, 1 insertions(+), 0 deletions(-) > > > > > > diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h > > > index 0bc3d37..a347bce 100644 > > > --- a/include/linux/kvm_host.h > > > +++ b/include/linux/kvm_host.h > > > @@ -593,6 +593,7 @@ static inline void kvm_guest_enter(void) > > > { > > > account_system_vtime(current); > > > current->flags |= PF_VCPU; > > > + rcu_note_context_switch(smp_processor_id()); > > > } > > > > > > static inline void kvm_guest_exit(void) > > > -- > > > 1.7.2.3 > > > > Please have it in x86's vcpu_enter_guest, then its more explicit > > (uncertain about the context of kvm_guest_enter call in other arches). > > > I checked all of them and kvm_guest_enter() is always called with local > irq disabled. Paul confirmed that rcu_note_context_switch() can be > called in such context. OK then. Perhaps have an assert to verify interrupts are disabled? -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
On Tue, May 03, 2011 at 10:29:52AM -0300, Marcelo Tosatti wrote: > On Tue, May 03, 2011 at 04:21:23PM +0300, Gleb Natapov wrote: > > On Tue, May 03, 2011 at 10:13:17AM -0300, Marcelo Tosatti wrote: > > > Hi Gleb, > > > > > > Thats a neat idea. > > > > > > On Thu, Apr 28, 2011 at 12:52:03PM +0300, Gleb Natapov wrote: > > > > KVM does not hold any references to rcu protected data when it switches > > > > CPU into a guest mode. In fact switching to a guest mode is very similar > > > > to exiting to userspase from rcu point of view. In addition CPU may stay > > > > in a guest mode for quite a long time (up to one time slice). Lets treat > > > > guest mode as quiescent state, just like we do with user-mode execution. > > > > > > > > Signed-off-by: Gleb Natapov <gleb@redhat.com> > > > > --- > > > > include/linux/kvm_host.h | 1 + > > > > 1 files changed, 1 insertions(+), 0 deletions(-) > > > > > > > > diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h > > > > index 0bc3d37..a347bce 100644 > > > > --- a/include/linux/kvm_host.h > > > > +++ b/include/linux/kvm_host.h > > > > @@ -593,6 +593,7 @@ static inline void kvm_guest_enter(void) > > > > { > > > > account_system_vtime(current); > > > > current->flags |= PF_VCPU; > > > > + rcu_note_context_switch(smp_processor_id()); > > > > } > > > > > > > > static inline void kvm_guest_exit(void) > > > > -- > > > > 1.7.2.3 > > > > > > Please have it in x86's vcpu_enter_guest, then its more explicit > > > (uncertain about the context of kvm_guest_enter call in other arches). > > > > > I checked all of them and kvm_guest_enter() is always called with local > > irq disabled. Paul confirmed that rcu_note_context_switch() can be > > called in such context. > > OK then. Perhaps have an assert to verify interrupts are disabled? Yes. Can add BUG_ON(preemptible()). -- Gleb. -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
On Tue, May 03, 2011 at 04:39:01PM +0300, Gleb Natapov wrote: > > > > On Thu, Apr 28, 2011 at 12:52:03PM +0300, Gleb Natapov wrote: > > > > > KVM does not hold any references to rcu protected data when it switches > > > > > CPU into a guest mode. In fact switching to a guest mode is very similar > > > > > to exiting to userspase from rcu point of view. In addition CPU may stay > > > > > in a guest mode for quite a long time (up to one time slice). Lets treat > > > > > guest mode as quiescent state, just like we do with user-mode execution. > > > > > > > > > > Signed-off-by: Gleb Natapov <gleb@redhat.com> > > > > > --- > > > > > include/linux/kvm_host.h | 1 + > > > > > 1 files changed, 1 insertions(+), 0 deletions(-) > > > > > > > > > > diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h > > > > > index 0bc3d37..a347bce 100644 > > > > > --- a/include/linux/kvm_host.h > > > > > +++ b/include/linux/kvm_host.h > > > > > @@ -593,6 +593,7 @@ static inline void kvm_guest_enter(void) > > > > > { > > > > > account_system_vtime(current); > > > > > current->flags |= PF_VCPU; > > > > > + rcu_note_context_switch(smp_processor_id()); > > > > > } > > > > > > > > > > static inline void kvm_guest_exit(void) > > > > > -- > > > > > 1.7.2.3 > > > > > > > > Please have it in x86's vcpu_enter_guest, then its more explicit > > > > (uncertain about the context of kvm_guest_enter call in other arches). > > > > > > > I checked all of them and kvm_guest_enter() is always called with local > > > irq disabled. Paul confirmed that rcu_note_context_switch() can be > > > called in such context. > > > > OK then. Perhaps have an assert to verify interrupts are disabled? > Yes. Can add BUG_ON(preemptible()). Also please add a comment to explain whats going on. The commit message above seems appropriate. -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h index 0bc3d37..a347bce 100644 --- a/include/linux/kvm_host.h +++ b/include/linux/kvm_host.h @@ -593,6 +593,7 @@ static inline void kvm_guest_enter(void) { account_system_vtime(current); current->flags |= PF_VCPU; + rcu_note_context_switch(smp_processor_id()); } static inline void kvm_guest_exit(void)
KVM does not hold any references to rcu protected data when it switches CPU into a guest mode. In fact switching to a guest mode is very similar to exiting to userspase from rcu point of view. In addition CPU may stay in a guest mode for quite a long time (up to one time slice). Lets treat guest mode as quiescent state, just like we do with user-mode execution. Signed-off-by: Gleb Natapov <gleb@redhat.com> --- include/linux/kvm_host.h | 1 + 1 files changed, 1 insertions(+), 0 deletions(-)