Re: [PATCH v2 12/18] KVM: arm64: Introduce __pkvm_host_relax_guest_perms()

[Quentin Perret <qperret@google.com>]

On Tuesday 10 Dec 2024 at 14:56:05 (+0000), Fuad Tabba wrote:
> Hi Quentin,
> 
> On Tue, 3 Dec 2024 at 10:38, Quentin Perret <qperret@google.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@google.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.

Ack to this and the other comment below, thanks for the review!

> 
> >  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
> >