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Message-ID: <CA+EHjTwNgf5fPuWMaPaN4mcdd5y4uydJsXi-zEBatFnbwoaLLQ@mail.gmail.com>
Date: Tue, 10 Dec 2024 14:56:05 +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 12/18] KVM: arm64: Introduce __pkvm_host_relax_guest_perms()
Hi Quentin,
On Tue, 3 Dec 2024 at 10:38, Quentin Perret <qperret@...gle.com> wrote:
>
> Introduce a new hypercall allowing the host to relax the stage-2
> permissions of mappings in a non-protected guest page-table. It will be
> used later once we start allowing RO memslots and 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 | 20 ++++++++++++++++
> arch/arm64/kvm/hyp/nvhe/mem_protect.c | 23 +++++++++++++++++++
> 4 files changed, 45 insertions(+)
>
> diff --git a/arch/arm64/include/asm/kvm_asm.h b/arch/arm64/include/asm/kvm_asm.h
> index 0b6c4d325134..5d51933e44fb 100644
> --- a/arch/arm64/include/asm/kvm_asm.h
> +++ b/arch/arm64/include/asm/kvm_asm.h
> @@ -67,6 +67,7 @@ enum __kvm_host_smccc_func {
> __KVM_HOST_SMCCC_FUNC___pkvm_host_unshare_hyp,
> __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___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 e528a42ed60e..db0dd83c2457 100644
> --- a/arch/arm64/kvm/hyp/include/nvhe/mem_protect.h
> +++ b/arch/arm64/kvm/hyp/include/nvhe/mem_protect.h
> @@ -41,6 +41,7 @@ int __pkvm_host_share_ffa(u64 pfn, u64 nr_pages);
> 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);
The parameters are the same as __pkvm_host_share_guest, but in a
different order. I looked ahead at later patches in the series, and similar
issues regarding parameter type and ordering, so I won't mention it
for the later patches.
> 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 04a9053ae1d5..60dd56bbd743 100644
> --- a/arch/arm64/kvm/hyp/nvhe/hyp-main.c
> +++ b/arch/arm64/kvm/hyp/nvhe/hyp-main.c
> @@ -267,6 +267,25 @@ static void handle___pkvm_host_unshare_guest(struct kvm_cpu_context *host_ctxt)
> cpu_reg(host_ctxt, 1) = ret;
> }
>
> +static void handle___pkvm_host_relax_guest_perms(struct kvm_cpu_context *host_ctxt)
> +{
> + DECLARE_REG(u64, gfn, host_ctxt, 1);
> + DECLARE_REG(enum kvm_pgtable_prot, prot, host_ctxt, 2);
> + struct pkvm_hyp_vcpu *hyp_vcpu;
> + int ret = -EINVAL;
> +
> + if (!is_protected_kvm_enabled())
> + goto out;
> +
> + hyp_vcpu = pkvm_get_loaded_hyp_vcpu();
> + if (!hyp_vcpu || pkvm_hyp_vcpu_is_protected(hyp_vcpu))
> + goto out;
> +
> + ret = __pkvm_host_relax_guest_perms(gfn, prot, hyp_vcpu);
> +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);
> @@ -478,6 +497,7 @@ static const hcall_t host_hcall[] = {
> HANDLE_FUNC(__pkvm_host_unshare_hyp),
> HANDLE_FUNC(__pkvm_host_share_guest),
> HANDLE_FUNC(__pkvm_host_unshare_guest),
> + HANDLE_FUNC(__pkvm_host_relax_guest_perms),
> 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 aa27a3e42e5e..d4b28e93e790 100644
> --- a/arch/arm64/kvm/hyp/nvhe/mem_protect.c
> +++ b/arch/arm64/kvm/hyp/nvhe/mem_protect.c
> @@ -1480,3 +1480,26 @@ int __pkvm_host_unshare_guest(u64 gfn, struct pkvm_hyp_vm *hyp_vm)
>
> return ret;
> }
> +
> +int __pkvm_host_relax_guest_perms(u64 gfn, enum kvm_pgtable_prot prot, struct pkvm_hyp_vcpu *vcpu)
> +{
> + struct pkvm_hyp_vm *vm = pkvm_hyp_vcpu_to_hyp_vm(vcpu);
> + u64 ipa = hyp_pfn_to_phys(gfn);
> + u64 phys;
> + int ret;
> +
> + if ((prot & KVM_PGTABLE_PROT_RWX) != prot)
> + return -EPERM;
Why not
+ if (prot & ~KVM_PGTABLE_PROT_RWX)
Simpler and consistent with similar checks in the file (e.g.,
__pkvm_host_share_guest)
Cheers,
/fuad
> +
> + host_lock_component();
> + guest_lock_component(vm);
> +
> + ret = __check_host_unshare_guest(vm, &phys, ipa);
> + if (!ret)
> + ret = kvm_pgtable_stage2_relax_perms(&vm->pgt, ipa, prot, 0);
> +
> + guest_unlock_component(vm);
> + host_unlock_component();
> +
> + return ret;
> +}
> --
> 2.47.0.338.g60cca15819-goog
>
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