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References: <20240412084056.1733704-1-steven.price@arm.com>
 <20240412084309.1733783-1-steven.price@arm.com> <20240412084309.1733783-2-steven.price@arm.com>
In-Reply-To: <20240412084309.1733783-2-steven.price@arm.com>
From: Fuad Tabba <tabba@google.com>
Date: Thu, 25 Apr 2024 10:48:50 +0100
Message-ID: <CA+EHjTwDaP6qULmjEGH=Eye=vjFikr9iJHEyzzX+cr_sH57vcA@mail.gmail.com>
Subject: Re: [PATCH v2 01/43] KVM: Prepare for handling only shared mappings
 in mmu_notifier events
To: Steven Price <steven.price@arm.com>
Cc: kvm@vger.kernel.org, kvmarm@lists.linux.dev, 
	Sean Christopherson <seanjc@google.com>, Catalin Marinas <catalin.marinas@arm.com>, 
	Marc Zyngier <maz@kernel.org>, Will Deacon <will@kernel.org>, James Morse <james.morse@arm.com>, 
	Oliver Upton <oliver.upton@linux.dev>, Suzuki K Poulose <suzuki.poulose@arm.com>, 
	Zenghui Yu <yuzenghui@huawei.com>, linux-arm-kernel@lists.infradead.org, 
	linux-kernel@vger.kernel.org, Joey Gouly <joey.gouly@arm.com>, 
	Alexandru Elisei <alexandru.elisei@arm.com>, Christoffer Dall <christoffer.dall@arm.com>, 
	linux-coco@lists.linux.dev, 
	Ganapatrao Kulkarni <gankulkarni@os.amperecomputing.com>
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Hi,

On Fri, Apr 12, 2024 at 9:43=E2=80=AFAM 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 =3D range->arg;
> +
> +                       /*
> +                        * HVA-based notifications aren't relevant to pri=
vate
> +                        * mappings as they don't have a userspace mappin=
g.
> +                        */
> +                       gfn_range.only_private =3D false;
> +                       gfn_range.only_shared =3D true;
>                         gfn_range.may_block =3D 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
>