Re: [PATCH v2 01/43] KVM: Prepare for handling only shared mappings in mmu_notifier events

Fuad Tabba
2024-04-25T09:49:28Z

Hi,

On Fri, Apr 12, 2024 at 9:43 AM Steven Price <steven.price@arm.com> wrote:
>
> From: Sean Christopherson <seanjc@google.com>
>
> 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>
> Signed-off-by: Steven Price <steven.price@arm.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 48f31dcd318a..c7581360fd88 100644
> --- a/include/linux/kvm_host.h
> +++ b/include/linux/kvm_host.h
> @@ -268,6 +268,8 @@ 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 fb49c2a60200..3486ceef6f4e 100644
> --- a/virt/kvm/kvm_main.c
> +++ b/virt/kvm/kvm_main.c
> @@ -633,6 +633,13 @@ 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;

I'd discussed this with Sean when he posted this earlier. Having two
booleans to encode three valid states could be confusing. In response,
Sean suggested using an enum instead:
https://lore.kernel.org/all/ZUO1Giju0GkUdF0o@google.com/

Cheers,
/fuad

>
> /*

> --
> 2.34.1
>