Add flags to "struct kvm_gfn_range" to let notifier events target only
shared and only private mappings, and write up the existing mmu_notifier
events to be shared-only (private memory is never associated with a
userspace virtual address, i.e. can't be reached via mmu_notifiers).

Add two flags so that KVM can handle the three possibilities (shared,
private, and shared+private) without needing something like a tri-state
enum.

Link: https://lore.kernel.org/all/ZJX0hk+KpQP0KUyB@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>
---
 include/linux/kvm_host.h | 2 ++
 virt/kvm/kvm_main.c      | 7 +++++++
 2 files changed, 9 insertions(+)

diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index 96aa930536b1..89c1a991a3b8 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -263,6 +263,8 @@ struct kvm_gfn_range {
 	gfn_t start;
 	gfn_t end;
 	union kvm_mmu_notifier_arg arg;
+	bool only_private;
+	bool only_shared;
 	bool may_block;
 };
 bool kvm_unmap_gfn_range(struct kvm *kvm, struct kvm_gfn_range *range);
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index cb9376833c18..302ccb87b4c1 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -635,6 +635,13 @@ static __always_inline kvm_mn_ret_t __kvm_handle_hva_range(struct kvm *kvm,
 			 * the second or later invocation of the handler).
 			 */
 			gfn_range.arg = range->arg;
+
+			/*
+			 * HVA-based notifications aren't relevant to private
+			 * mappings as they don't have a userspace mapping.
+			 */
+			gfn_range.only_private = false;
+			gfn_range.only_shared = true;
 			gfn_range.may_block = range->may_block;
 
 			/*
-- 
2.42.0.820.g83a721a137-goog

Hi,

On Fri, Oct 27, 2023 at 7:22 PM Sean Christopherson <seanjc@google.com> wrote:
>
> Add flags to "struct kvm_gfn_range" to let notifier events target only
> shared and only private mappings, and write up the existing mmu_notifier
> events to be shared-only (private memory is never associated with a
> userspace virtual address, i.e. can't be reached via mmu_notifiers).
>
> Add two flags so that KVM can handle the three possibilities (shared,
> private, and shared+private) without needing something like a tri-state
> enum.
>
> Link: https://lore.kernel.org/all/ZJX0hk+KpQP0KUyB@google.com
> Signed-off-by: Sean Christopherson <seanjc@google.com>
> ---
>  include/linux/kvm_host.h | 2 ++
>  virt/kvm/kvm_main.c      | 7 +++++++
>  2 files changed, 9 insertions(+)
>
> diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
> index 96aa930536b1..89c1a991a3b8 100644
> --- a/include/linux/kvm_host.h
> +++ b/include/linux/kvm_host.h
> @@ -263,6 +263,8 @@ struct kvm_gfn_range {
>         gfn_t start;
>         gfn_t end;
>         union kvm_mmu_notifier_arg arg;
> +       bool only_private;
> +       bool only_shared;

If these flags aren't used in this patch series, should this patch be
moved to the other series?

Also, if shared+private is a possibility, doesn't the prefix "only_"
confuse things a bit? I.e., what is shared+private, is it when both
are 0 or when both are 1? I assume it's the former (both are 0), but
it might be clearer.

Cheers,
/fuad

>         bool may_block;
>  };
>  bool kvm_unmap_gfn_range(struct kvm *kvm, struct kvm_gfn_range *range);
> diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> index cb9376833c18..302ccb87b4c1 100644
> --- a/virt/kvm/kvm_main.c
> +++ b/virt/kvm/kvm_main.c
> @@ -635,6 +635,13 @@ static __always_inline kvm_mn_ret_t __kvm_handle_hva_range(struct kvm *kvm,
>                          * the second or later invocation of the handler).
>                          */
>                         gfn_range.arg = range->arg;
> +
> +                       /*
> +                        * HVA-based notifications aren't relevant to private
> +                        * mappings as they don't have a userspace mapping.
> +                        */
> +                       gfn_range.only_private = false;
> +                       gfn_range.only_shared = true;
>                         gfn_range.may_block = range->may_block;
>
>                         /*
> --
> 2.42.0.820.g83a721a137-goog
>

On Thu, Nov 02, 2023, Fuad Tabba wrote:
> Hi,
> 
> On Fri, Oct 27, 2023 at 7:22 PM Sean Christopherson <seanjc@google.com> wrote:
> >
> > Add flags to "struct kvm_gfn_range" to let notifier events target only
> > shared and only private mappings, and write up the existing mmu_notifier
> > events to be shared-only (private memory is never associated with a
> > userspace virtual address, i.e. can't be reached via mmu_notifiers).
> >
> > Add two flags so that KVM can handle the three possibilities (shared,
> > private, and shared+private) without needing something like a tri-state
> > enum.
> >
> > Link: https://lore.kernel.org/all/ZJX0hk+KpQP0KUyB@google.com
> > Signed-off-by: Sean Christopherson <seanjc@google.com>
> > ---
> >  include/linux/kvm_host.h | 2 ++
> >  virt/kvm/kvm_main.c      | 7 +++++++
> >  2 files changed, 9 insertions(+)
> >
> > diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
> > index 96aa930536b1..89c1a991a3b8 100644
> > --- a/include/linux/kvm_host.h
> > +++ b/include/linux/kvm_host.h
> > @@ -263,6 +263,8 @@ struct kvm_gfn_range {
> >         gfn_t start;
> >         gfn_t end;
> >         union kvm_mmu_notifier_arg arg;
> > +       bool only_private;
> > +       bool only_shared;
> 
> If these flags aren't used in this patch series, should this patch be
> moved to the other series?

If *both* TDX and SNP need this patch, then I think it's probably worth applying
it now to make their lives easier.  But if only one needs the support, then I
completely agree this should be punted to whichever series needs it (this also
came up in v11, but we didn't force the issue).

Mike, Isaku?

> Also, if shared+private is a possibility, doesn't the prefix "only_"
> confuse things a bit? I.e., what is shared+private, is it when both
> are 0 or when both are 1? I assume it's the former (both are 0), but
> it might be clearer.

Heh, I was hoping that "only_private && only_shared" would be obviously nonsensical.

The only alternative I can think would be to add an enum, e.g.

	enum {
		PROCESS_PRIVATE_AND_SHARED,
		PROCESS_ONLY_PRIVATE,
		PROCESS_ONLY_SHARED,
	};

because every other way of expressing the flags either results in more confusion
or an unsafe default.  I.e. I want zapping only private or only shared to require
the caller to explicitly set a non-zero value, which is how I ended up with
"only_{private,shared}" as opposed to "process_{private,shared}".

On Thu, Nov 2, 2023 at 2:41 PM Sean Christopherson <seanjc@google.com> wrote:
>
> On Thu, Nov 02, 2023, Fuad Tabba wrote:
> > Hi,
> >
> > On Fri, Oct 27, 2023 at 7:22 PM Sean Christopherson <seanjc@google.com> wrote:
> > >
> > > Add flags to "struct kvm_gfn_range" to let notifier events target only
> > > shared and only private mappings, and write up the existing mmu_notifier
> > > events to be shared-only (private memory is never associated with a
> > > userspace virtual address, i.e. can't be reached via mmu_notifiers).
> > >
> > > Add two flags so that KVM can handle the three possibilities (shared,
> > > private, and shared+private) without needing something like a tri-state
> > > enum.
> > >
> > > Link: https://lore.kernel.org/all/ZJX0hk+KpQP0KUyB@google.com
> > > Signed-off-by: Sean Christopherson <seanjc@google.com>
> > > ---
> > >  include/linux/kvm_host.h | 2 ++
> > >  virt/kvm/kvm_main.c      | 7 +++++++
> > >  2 files changed, 9 insertions(+)
> > >
> > > diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
> > > index 96aa930536b1..89c1a991a3b8 100644
> > > --- a/include/linux/kvm_host.h
> > > +++ b/include/linux/kvm_host.h
> > > @@ -263,6 +263,8 @@ struct kvm_gfn_range {
> > >         gfn_t start;
> > >         gfn_t end;
> > >         union kvm_mmu_notifier_arg arg;
> > > +       bool only_private;
> > > +       bool only_shared;
> >
> > If these flags aren't used in this patch series, should this patch be
> > moved to the other series?
>
> If *both* TDX and SNP need this patch, then I think it's probably worth applying
> it now to make their lives easier.  But if only one needs the support, then I
> completely agree this should be punted to whichever series needs it (this also
> came up in v11, but we didn't force the issue).
>
> Mike, Isaku?
>
> > Also, if shared+private is a possibility, doesn't the prefix "only_"
> > confuse things a bit? I.e., what is shared+private, is it when both
> > are 0 or when both are 1? I assume it's the former (both are 0), but
> > it might be clearer.
>
> Heh, I was hoping that "only_private && only_shared" would be obviously nonsensical.
>
> The only alternative I can think would be to add an enum, e.g.
>
>         enum {
>                 PROCESS_PRIVATE_AND_SHARED,
>                 PROCESS_ONLY_PRIVATE,
>                 PROCESS_ONLY_SHARED,
>         };
>
> because every other way of expressing the flags either results in more confusion
> or an unsafe default.  I.e. I want zapping only private or only shared to require
> the caller to explicitly set a non-zero value, which is how I ended up with
> "only_{private,shared}" as opposed to "process_{private,shared}".

I don't have a strong opinion about this. Having an enum looks good to me.

Cheers,
/fuad

On 10/28/2023 2:21 AM, Sean Christopherson wrote:
> Add flags to "struct kvm_gfn_range" to let notifier events target only
> shared and only private mappings, and write up the existing mmu_notifier
> events to be shared-only (private memory is never associated with a
> userspace virtual address, i.e. can't be reached via mmu_notifiers).
>
> Add two flags so that KVM can handle the three possibilities (shared,
> private, and shared+private) without needing something like a tri-state
> enum.
I see the two flags are set/cleared in __kvm_handle_hva_range() in this 
patch
and kvm_handle_gfn_range() from the later patch 13/35, but I didn't see they
are used/read in this patch series if I didn't miss anything.  How are they
supposed to be used in KVM?


>
> Link: https://lore.kernel.org/all/ZJX0hk+KpQP0KUyB@google.com
> Signed-off-by: Sean Christopherson <seanjc@google.com>
> ---
>   include/linux/kvm_host.h | 2 ++
>   virt/kvm/kvm_main.c      | 7 +++++++
>   2 files changed, 9 insertions(+)
>
> diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
> index 96aa930536b1..89c1a991a3b8 100644
> --- a/include/linux/kvm_host.h
> +++ b/include/linux/kvm_host.h
> @@ -263,6 +263,8 @@ struct kvm_gfn_range {
>   	gfn_t start;
>   	gfn_t end;
>   	union kvm_mmu_notifier_arg arg;
> +	bool only_private;
> +	bool only_shared;
>   	bool may_block;
>   };
>   bool kvm_unmap_gfn_range(struct kvm *kvm, struct kvm_gfn_range *range);
> diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> index cb9376833c18..302ccb87b4c1 100644
> --- a/virt/kvm/kvm_main.c
> +++ b/virt/kvm/kvm_main.c
> @@ -635,6 +635,13 @@ static __always_inline kvm_mn_ret_t __kvm_handle_hva_range(struct kvm *kvm,
>   			 * the second or later invocation of the handler).
>   			 */
>   			gfn_range.arg = range->arg;
> +
> +			/*
> +			 * HVA-based notifications aren't relevant to private
> +			 * mappings as they don't have a userspace mapping.
> +			 */
> +			gfn_range.only_private = false;
> +			gfn_range.only_shared = true;
>   			gfn_range.may_block = range->may_block;
>   
>   			/*

On 11/2/23 06:59, Binbin Wu wrote:
> 
>> Add flags to "struct kvm_gfn_range" to let notifier events target
>> only shared and only private mappings, and write up the existing
>> mmu_notifier events to be shared-only (private memory is never
>> associated with a userspace virtual address, i.e. can't be reached
>> via mmu_notifiers).
>> 
>> Add two flags so that KVM can handle the three possibilities
>> (shared, private, and shared+private) without needing something
>> like a tri-state enum.
>
> I see the two flags are set/cleared in __kvm_handle_hva_range() in
> this patch and kvm_handle_gfn_range() from the later patch 13/35, but
> I didn't see they are used/read in this patch series if I didn't miss
> anything.  How are they supposed to be used in KVM?

They are going to be used by SNP/TDX patches.

Paolo

On 10/27/23 20:21, Sean Christopherson wrote:
> @@ -635,6 +635,13 @@ static __always_inline kvm_mn_ret_t __kvm_handle_hva_range(struct kvm *kvm,
>  			 * the second or later invocation of the handler).
>  			 */
>  			gfn_range.arg = range->arg;
> +
> +			/*
> +			 * HVA-based notifications aren't relevant to private
> +			 * mappings as they don't have a userspace mapping.

It's confusing who "they" is.  Maybe

	 * HVA-based notifications provide a userspace address,
	 * and as such are only relevant for shared mappings.

Paolo

> +			 */
> +			gfn_range.only_private = false;
> +			gfn_range.only_shared = true;
>  			gfn_range.may_block = range->may_block;
>  
>  			/*

On Mon, Oct 30, 2023, Paolo Bonzini wrote:
> On 10/27/23 20:21, Sean Christopherson wrote:
> > @@ -635,6 +635,13 @@ static __always_inline kvm_mn_ret_t __kvm_handle_hva_range(struct kvm *kvm,
> >  			 * the second or later invocation of the handler).
> >  			 */
> >  			gfn_range.arg = range->arg;
> > +
> > +			/*
> > +			 * HVA-based notifications aren't relevant to private
> > +			 * mappings as they don't have a userspace mapping.
> 
> It's confusing who "they" is.  Maybe
> 
> 	 * HVA-based notifications provide a userspace address,
> 	 * and as such are only relevant for shared mappings.

Works for me.