diff mbox series

[3/4] kvm: Add new pfn error KVM_PFN_ERR_INTR

Message ID 20220622213656.81546-4-peterx@redhat.com (mailing list archive)
State New
Headers show
Series kvm/mm: Allow GUP to respond to non fatal signals | expand

Commit Message

Peter Xu June 22, 2022, 9:36 p.m. UTC
Add one new PFN error type to show when we cannot finish fetching the PFN
due to interruptions.  For example, by receiving a generic signal.

This prepares KVM to be able to respond to SIGUSR1 (for QEMU that's the
SIGIPI) even during e.g. handling an userfaultfd page fault.

Signed-off-by: Peter Xu <peterx@redhat.com>
---
 include/linux/kvm_host.h | 11 +++++++++++
 1 file changed, 11 insertions(+)

Comments

Sean Christopherson June 23, 2022, 2:31 p.m. UTC | #1
On Wed, Jun 22, 2022, Peter Xu wrote:
> Add one new PFN error type to show when we cannot finish fetching the PFN
> due to interruptions.  For example, by receiving a generic signal.
> 
> This prepares KVM to be able to respond to SIGUSR1 (for QEMU that's the
> SIGIPI) even during e.g. handling an userfaultfd page fault.
> 
> Signed-off-by: Peter Xu <peterx@redhat.com>
> ---
>  include/linux/kvm_host.h | 11 +++++++++++
>  1 file changed, 11 insertions(+)
> 
> diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
> index b646b6fcaec6..4f84a442f67f 100644
> --- a/include/linux/kvm_host.h
> +++ b/include/linux/kvm_host.h
> @@ -96,6 +96,7 @@
>  #define KVM_PFN_ERR_FAULT	(KVM_PFN_ERR_MASK)
>  #define KVM_PFN_ERR_HWPOISON	(KVM_PFN_ERR_MASK + 1)
>  #define KVM_PFN_ERR_RO_FAULT	(KVM_PFN_ERR_MASK + 2)
> +#define KVM_PFN_ERR_INTR	(KVM_PFN_ERR_MASK + 3)
>  
>  /*
>   * error pfns indicate that the gfn is in slot but faild to
> @@ -106,6 +107,16 @@ static inline bool is_error_pfn(kvm_pfn_t pfn)
>  	return !!(pfn & KVM_PFN_ERR_MASK);
>  }
>  
> +/*
> + * When KVM_PFN_ERR_INTR is returned, it means we're interrupted during
> + * fetching the PFN (e.g. a signal might have arrived), so we may want to
> + * retry at some later point and kick the userspace to handle the signal.
> + */
> +static inline bool is_intr_pfn(kvm_pfn_t pfn)
> +{
> +	return pfn == KVM_PFN_ERR_INTR;

What about is_sigpending_pfn() and KVM_PFN_ERR_SIGPENDING?  "intr" is too close to
a real thing KVM will encounter, and I think knowing that KVM is effectively
responding to a pending signal is the most important detail for KVM developers
encountering this code for this first time.  E.g. from KVM_PFN_ERR_INTR alone, one
might think that any interrupt during GUP will trigger this.

> +}
> +
>  /*
>   * error_noslot pfns indicate that the gfn can not be
>   * translated to pfn - it is not in slot or failed to
> -- 
> 2.32.0
>
Peter Xu June 23, 2022, 7:32 p.m. UTC | #2
On Thu, Jun 23, 2022 at 02:31:47PM +0000, Sean Christopherson wrote:
> On Wed, Jun 22, 2022, Peter Xu wrote:
> > Add one new PFN error type to show when we cannot finish fetching the PFN
> > due to interruptions.  For example, by receiving a generic signal.
> > 
> > This prepares KVM to be able to respond to SIGUSR1 (for QEMU that's the
> > SIGIPI) even during e.g. handling an userfaultfd page fault.
> > 
> > Signed-off-by: Peter Xu <peterx@redhat.com>
> > ---
> >  include/linux/kvm_host.h | 11 +++++++++++
> >  1 file changed, 11 insertions(+)
> > 
> > diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
> > index b646b6fcaec6..4f84a442f67f 100644
> > --- a/include/linux/kvm_host.h
> > +++ b/include/linux/kvm_host.h
> > @@ -96,6 +96,7 @@
> >  #define KVM_PFN_ERR_FAULT	(KVM_PFN_ERR_MASK)
> >  #define KVM_PFN_ERR_HWPOISON	(KVM_PFN_ERR_MASK + 1)
> >  #define KVM_PFN_ERR_RO_FAULT	(KVM_PFN_ERR_MASK + 2)
> > +#define KVM_PFN_ERR_INTR	(KVM_PFN_ERR_MASK + 3)
> >  
> >  /*
> >   * error pfns indicate that the gfn is in slot but faild to
> > @@ -106,6 +107,16 @@ static inline bool is_error_pfn(kvm_pfn_t pfn)
> >  	return !!(pfn & KVM_PFN_ERR_MASK);
> >  }
> >  
> > +/*
> > + * When KVM_PFN_ERR_INTR is returned, it means we're interrupted during
> > + * fetching the PFN (e.g. a signal might have arrived), so we may want to
> > + * retry at some later point and kick the userspace to handle the signal.
> > + */
> > +static inline bool is_intr_pfn(kvm_pfn_t pfn)
> > +{
> > +	return pfn == KVM_PFN_ERR_INTR;
> 
> What about is_sigpending_pfn() and KVM_PFN_ERR_SIGPENDING?  "intr" is too close to
> a real thing KVM will encounter, and I think knowing that KVM is effectively
> responding to a pending signal is the most important detail for KVM developers
> encountering this code for this first time.  E.g. from KVM_PFN_ERR_INTR alone, one
> might think that any interrupt during GUP will trigger this.

Sounds good; INTR could be too general for KVM indeed.  Thanks,
diff mbox series

Patch

diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index b646b6fcaec6..4f84a442f67f 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -96,6 +96,7 @@ 
 #define KVM_PFN_ERR_FAULT	(KVM_PFN_ERR_MASK)
 #define KVM_PFN_ERR_HWPOISON	(KVM_PFN_ERR_MASK + 1)
 #define KVM_PFN_ERR_RO_FAULT	(KVM_PFN_ERR_MASK + 2)
+#define KVM_PFN_ERR_INTR	(KVM_PFN_ERR_MASK + 3)
 
 /*
  * error pfns indicate that the gfn is in slot but faild to
@@ -106,6 +107,16 @@  static inline bool is_error_pfn(kvm_pfn_t pfn)
 	return !!(pfn & KVM_PFN_ERR_MASK);
 }
 
+/*
+ * When KVM_PFN_ERR_INTR is returned, it means we're interrupted during
+ * fetching the PFN (e.g. a signal might have arrived), so we may want to
+ * retry at some later point and kick the userspace to handle the signal.
+ */
+static inline bool is_intr_pfn(kvm_pfn_t pfn)
+{
+	return pfn == KVM_PFN_ERR_INTR;
+}
+
 /*
  * error_noslot pfns indicate that the gfn can not be
  * translated to pfn - it is not in slot or failed to