linux-kernel - Re: [PATCH v2 13/18] KVM: arm64: Introduce __pkvm_host_wrprotect

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Message-ID: <CA+EHjTx-MZHKwkGYPU+yN-CDkNh1kxTXN8FWTeaPfM95OSkjcQ@mail.gmail.com>
Date: Tue, 10 Dec 2024 15:06:53 +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 13/18] KVM: arm64: Introduce __pkvm_host_wrprotect_guest()

Hi Quentin,

On Tue, 3 Dec 2024 at 10:38, Quentin Perret <qperret@...gle.com> wrote:
>
> Introduce a new hypercall to remove the write permission from a
> non-protected guest stage-2 mapping. This will be used for e.g. enabling
> dirty logging.
>
> Signed-off-by: Quentin Perret <qperret@...gle.com>
> ---
>  arch/arm64/include/asm/kvm_asm.h              |  1 +
>  arch/arm64/kvm/hyp/include/nvhe/mem_protect.h |  1 +
>  arch/arm64/kvm/hyp/nvhe/hyp-main.c            | 24 +++++++++++++++++++
>  arch/arm64/kvm/hyp/nvhe/mem_protect.c         | 19 +++++++++++++++
>  4 files changed, 45 insertions(+)
>
> diff --git a/arch/arm64/include/asm/kvm_asm.h b/arch/arm64/include/asm/kvm_asm.h
> index 5d51933e44fb..4d7d20ea03df 100644
> --- a/arch/arm64/include/asm/kvm_asm.h
> +++ b/arch/arm64/include/asm/kvm_asm.h
> @@ -68,6 +68,7 @@ enum __kvm_host_smccc_func {
>         __KVM_HOST_SMCCC_FUNC___pkvm_host_share_guest,
>         __KVM_HOST_SMCCC_FUNC___pkvm_host_unshare_guest,
>         __KVM_HOST_SMCCC_FUNC___pkvm_host_relax_guest_perms,
> +       __KVM_HOST_SMCCC_FUNC___pkvm_host_wrprotect_guest,
>         __KVM_HOST_SMCCC_FUNC___kvm_adjust_pc,
>         __KVM_HOST_SMCCC_FUNC___kvm_vcpu_run,
>         __KVM_HOST_SMCCC_FUNC___kvm_flush_vm_context,
> diff --git a/arch/arm64/kvm/hyp/include/nvhe/mem_protect.h b/arch/arm64/kvm/hyp/include/nvhe/mem_protect.h
> index db0dd83c2457..8658b5932473 100644
> --- a/arch/arm64/kvm/hyp/include/nvhe/mem_protect.h
> +++ b/arch/arm64/kvm/hyp/include/nvhe/mem_protect.h
> @@ -42,6 +42,7 @@ int __pkvm_host_unshare_ffa(u64 pfn, u64 nr_pages);
>  int __pkvm_host_share_guest(u64 pfn, u64 gfn, struct pkvm_hyp_vcpu *vcpu, enum kvm_pgtable_prot prot);
>  int __pkvm_host_unshare_guest(u64 gfn, struct pkvm_hyp_vm *hyp_vm);
>  int __pkvm_host_relax_guest_perms(u64 gfn, enum kvm_pgtable_prot prot, struct pkvm_hyp_vcpu *vcpu);
> +int __pkvm_host_wrprotect_guest(u64 gfn, struct pkvm_hyp_vm *hyp_vm);
>
>  bool addr_is_memory(phys_addr_t phys);
>  int host_stage2_idmap_locked(phys_addr_t addr, u64 size, enum kvm_pgtable_prot prot);
> diff --git a/arch/arm64/kvm/hyp/nvhe/hyp-main.c b/arch/arm64/kvm/hyp/nvhe/hyp-main.c
> index 60dd56bbd743..3feaf2119e51 100644
> --- a/arch/arm64/kvm/hyp/nvhe/hyp-main.c
> +++ b/arch/arm64/kvm/hyp/nvhe/hyp-main.c
> @@ -286,6 +286,29 @@ static void handle___pkvm_host_relax_guest_perms(struct kvm_cpu_context *host_ct
>         cpu_reg(host_ctxt, 1) = ret;
>  }
>
> +static void handle___pkvm_host_wrprotect_guest(struct kvm_cpu_context *host_ctxt)
> +{
> +       DECLARE_REG(pkvm_handle_t, handle, host_ctxt, 1);
> +       DECLARE_REG(u64, gfn, host_ctxt, 2);
> +       struct pkvm_hyp_vm *hyp_vm;
> +       int ret = -EINVAL;
> +
> +       if (!is_protected_kvm_enabled())
> +               goto out;
> +
> +       hyp_vm = get_pkvm_hyp_vm(handle);
> +       if (!hyp_vm)
> +               goto out;
> +       if (pkvm_hyp_vm_is_protected(hyp_vm))
> +               goto put_hyp_vm;

These checks are (unsurprisingly) the same for all these functions.
Does it make sense to have a helper do these checks?

Cheers,
/fuad

> +       ret = __pkvm_host_wrprotect_guest(gfn, hyp_vm);
> +put_hyp_vm:
> +       put_pkvm_hyp_vm(hyp_vm);
> +out:
> +       cpu_reg(host_ctxt, 1) = ret;
> +}
> +
>  static void handle___kvm_adjust_pc(struct kvm_cpu_context *host_ctxt)
>  {
>         DECLARE_REG(struct kvm_vcpu *, vcpu, host_ctxt, 1);
> @@ -498,6 +521,7 @@ static const hcall_t host_hcall[] = {
>         HANDLE_FUNC(__pkvm_host_share_guest),
>         HANDLE_FUNC(__pkvm_host_unshare_guest),
>         HANDLE_FUNC(__pkvm_host_relax_guest_perms),
> +       HANDLE_FUNC(__pkvm_host_wrprotect_guest),
>         HANDLE_FUNC(__kvm_adjust_pc),
>         HANDLE_FUNC(__kvm_vcpu_run),
>         HANDLE_FUNC(__kvm_flush_vm_context),
> diff --git a/arch/arm64/kvm/hyp/nvhe/mem_protect.c b/arch/arm64/kvm/hyp/nvhe/mem_protect.c
> index d4b28e93e790..89312d7cde2a 100644
> --- a/arch/arm64/kvm/hyp/nvhe/mem_protect.c
> +++ b/arch/arm64/kvm/hyp/nvhe/mem_protect.c
> @@ -1503,3 +1503,22 @@ int __pkvm_host_relax_guest_perms(u64 gfn, enum kvm_pgtable_prot prot, struct pk
>
>         return ret;
>  }
> +
> +int __pkvm_host_wrprotect_guest(u64 gfn, struct pkvm_hyp_vm *vm)
> +{
> +       u64 ipa = hyp_pfn_to_phys(gfn);
> +       u64 phys;
> +       int ret;
> +
> +       host_lock_component();
> +       guest_lock_component(vm);
> +
> +       ret = __check_host_unshare_guest(vm, &phys, ipa);
> +       if (!ret)
> +               ret = kvm_pgtable_stage2_wrprotect(&vm->pgt, ipa, PAGE_SIZE);
> +
> +       guest_unlock_component(vm);
> +       host_unlock_component();
> +
> +       return ret;
> +}
> --
> 2.47.0.338.g60cca15819-goog
>