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/[email protected]
Signed-off-by: Sean Christopherson <[email protected]>
---
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
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.
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/[email protected]
> Signed-off-by: Sean Christopherson <[email protected]>
> ---
> 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
Hi,
On Fri, Oct 27, 2023 at 7:22 PM Sean Christopherson <[email protected]> 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/[email protected]
> Signed-off-by: Sean Christopherson <[email protected]>
> ---
> 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 <[email protected]> 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/[email protected]
> > Signed-off-by: Sean Christopherson <[email protected]>
> > ---
> > 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 <[email protected]> wrote:
>
> On Thu, Nov 02, 2023, Fuad Tabba wrote:
> > Hi,
> >
> > On Fri, Oct 27, 2023 at 7:22 PM Sean Christopherson <[email protected]> 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/[email protected]
> > > Signed-off-by: Sean Christopherson <[email protected]>
> > > ---
> > > 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