Re: [PATCH v7 01/45] KVM: Prepare for handling only shared mappings in mmu_notifier events

[Gavin Shan <gshan@redhat.com>]

On 2/14/25 2:13 AM, Steven Price 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 3cb9a32a6330..0de1e485452c 100644
> --- a/include/linux/kvm_host.h
> +++ b/include/linux/kvm_host.h
> @@ -266,6 +266,8 @@ struct kvm_gfn_range {
>   	gfn_t end;
>   	union kvm_mmu_notifier_arg arg;
>   	enum kvm_gfn_range_filter attr_filter;
> +	bool only_private;
> +	bool only_shared;
>   	bool may_block;
>   };

The added members (only_private and only_shared) looks duplicated to the
member of attr_filter, which can be set to KVM_FILTER_SHARED, KVM_FILTER_PRIVATE,
or both of them. More details can be found from the following commit where
attr_filter was by dca6c88532322 ("KVM: Add member to struct kvm_gfn_range
to indicate private/shared").

I'm guessing Sean's suggestion was given before dca6c88532322 showed up.

>   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 faf10671eed2..4f0136094fac 100644
> --- a/virt/kvm/kvm_main.c
> +++ b/virt/kvm/kvm_main.c
> @@ -593,6 +593,13 @@ 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;
>   			/*
>   			 * HVA-based notifications aren't relevant to private

Thanks,
Gavin