linux-kernel - Re: [PATCH v2 16/18] KVM: arm64: Introduce __pkvm_tlb_flush

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Message-ID: <CA+EHjTw_e_q5TFkgxvVDKxwj-C5S0Hd1OfVO4_FitrB8_J2Rpw@mail.gmail.com>
Date: Tue, 10 Dec 2024 15:23:02 +0000
From: Fuad Tabba <tabba@...gle.com>
To: Quentin Perret <qperret@...gle.com>
Cc: Marc Zyngier <maz@...nel.org>, Oliver Upton <oliver.upton@...ux.dev>, 
	Joey Gouly <joey.gouly@....com>, Suzuki K Poulose <suzuki.poulose@....com>, 
	Zenghui Yu <yuzenghui@...wei.com>, Catalin Marinas <catalin.marinas@....com>, 
	Will Deacon <will@...nel.org>, Vincent Donnefort <vdonnefort@...gle.com>, 
	Sebastian Ene <sebastianene@...gle.com>, linux-arm-kernel@...ts.infradead.org, 
	kvmarm@...ts.linux.dev, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 16/18] KVM: arm64: Introduce __pkvm_tlb_flush_vmid()

Hi Quentin,

On Tue, 3 Dec 2024 at 10:38, Quentin Perret <qperret@...gle.com> wrote:
>
> Introduce a new hypercall to flush the TLBs of non-protected guests. The
> host kernel will be responsible for issuing this hypercall after changing
> stage-2 permissions using the __pkvm_host_relax_guest_perms() or
> __pkvm_host_wrprotect_guest() paths. This is left under the host's
> responsibility for performance reasons.
>
> Note however that the TLB maintenance for all *unmap* operations still
> remains entirely under the hypervisor's responsibility for security
> reasons -- an unmapped page may be donated to another entity, so a stale
> TLB entry could be used to leak private data.
>
> Signed-off-by: Quentin Perret <qperret@...gle.com>
> ---
>  arch/arm64/include/asm/kvm_asm.h   |  1 +
>  arch/arm64/kvm/hyp/nvhe/hyp-main.c | 17 +++++++++++++++++
>  2 files changed, 18 insertions(+)
>
> diff --git a/arch/arm64/include/asm/kvm_asm.h b/arch/arm64/include/asm/kvm_asm.h
> index 6178e12a0dbc..df6237d0459c 100644
> --- a/arch/arm64/include/asm/kvm_asm.h
> +++ b/arch/arm64/include/asm/kvm_asm.h
> @@ -87,6 +87,7 @@ enum __kvm_host_smccc_func {
>         __KVM_HOST_SMCCC_FUNC___pkvm_teardown_vm,
>         __KVM_HOST_SMCCC_FUNC___pkvm_vcpu_load,
>         __KVM_HOST_SMCCC_FUNC___pkvm_vcpu_put,
> +       __KVM_HOST_SMCCC_FUNC___pkvm_tlb_flush_vmid,
>  };
>
>  #define DECLARE_KVM_VHE_SYM(sym)       extern char sym[]
> diff --git a/arch/arm64/kvm/hyp/nvhe/hyp-main.c b/arch/arm64/kvm/hyp/nvhe/hyp-main.c
> index de0012a75827..219d7fb850ec 100644
> --- a/arch/arm64/kvm/hyp/nvhe/hyp-main.c
> +++ b/arch/arm64/kvm/hyp/nvhe/hyp-main.c
> @@ -398,6 +398,22 @@ static void handle___kvm_tlb_flush_vmid(struct kvm_cpu_context *host_ctxt)
>         __kvm_tlb_flush_vmid(kern_hyp_va(mmu));
>  }
>
> +static void handle___pkvm_tlb_flush_vmid(struct kvm_cpu_context *host_ctxt)
> +{
> +       DECLARE_REG(pkvm_handle_t, handle, host_ctxt, 1);
> +       struct pkvm_hyp_vm *hyp_vm;
> +
> +       if (!is_protected_kvm_enabled())
> +               return;
> +
> +       hyp_vm = get_pkvm_hyp_vm(handle);
> +       if (!hyp_vm)
> +               return;
> +
> +       __kvm_tlb_flush_vmid(&hyp_vm->kvm.arch.mmu);
> +       put_pkvm_hyp_vm(hyp_vm);
> +}

Since this is practically the same as kvm_tlb_flush_vmid(), does it
make sense to modify that instead (handle___kvm_tlb_flush_vmid()) to
do the right thing depending on whether pkvm is enabled? Thinking as
well for the future in case we want to support the rest of the
kvm_tlb_flush_vmid_*().

Cheers,
/fuad

> +
>  static void handle___kvm_flush_cpu_context(struct kvm_cpu_context *host_ctxt)
>  {
>         DECLARE_REG(struct kvm_s2_mmu *, mmu, host_ctxt, 1);
> @@ -582,6 +598,7 @@ static const hcall_t host_hcall[] = {
>         HANDLE_FUNC(__pkvm_teardown_vm),
>         HANDLE_FUNC(__pkvm_vcpu_load),
>         HANDLE_FUNC(__pkvm_vcpu_put),
> +       HANDLE_FUNC(__pkvm_tlb_flush_vmid),
>  };
>
>  static void handle_host_hcall(struct kvm_cpu_context *host_ctxt)
> --
> 2.47.0.338.g60cca15819-goog
>