Re: [PATCH Part2 v6 39/49] KVM: SVM: Introduce ops for the post gfn map and unmap

[Peter Gonda]

On Wed, Aug 17, 2022 at 9:47 PM Alper Gun <alpergun@xxxxxxxxxx> wrote:
>
> On Mon, Jun 20, 2022 at 4:12 PM Ashish Kalra <Ashish.Kalra@xxxxxxx> wrote:
> >
> > From: Brijesh Singh <brijesh.singh@xxxxxxx>
> >
> > When SEV-SNP is enabled in the guest VM, the guest memory pages can
> > either be a private or shared. A write from the hypervisor goes through
> > the RMP checks. If hardware sees that hypervisor is attempting to write
> > to a guest private page, then it triggers an RMP violation #PF.
> >
> > To avoid the RMP violation with GHCB pages, added new post_{map,unmap}_gfn
> > functions to verify if its safe to map GHCB pages.  Uses a spinlock to
> > protect against the page state change for existing mapped pages.
> >
> > Need to add generic post_{map,unmap}_gfn() ops that can be used to verify
> > that its safe to map a given guest page in the hypervisor.
> >
> > This patch will need to be revisited later after consensus is reached on
> > how to manage guest private memory as probably UPM private memslots will
> > be able to handle this page state change more gracefully.
> >
> > Signed-off-by: Brijesh Singh <brijesh.singh@xxxxxxx>
> > Signed-off by: Ashish Kalra <ashish.kalra@xxxxxxx>
> > ---
> >  arch/x86/include/asm/kvm-x86-ops.h |  1 +
> >  arch/x86/include/asm/kvm_host.h    |  3 ++
> >  arch/x86/kvm/svm/sev.c             | 48 ++++++++++++++++++++++++++++--
> >  arch/x86/kvm/svm/svm.c             |  3 ++
> >  arch/x86/kvm/svm/svm.h             | 11 +++++++
> >  5 files changed, 64 insertions(+), 2 deletions(-)
> >
> > diff --git a/arch/x86/include/asm/kvm-x86-ops.h b/arch/x86/include/asm/kvm-x86-ops.h
> > index e0068e702692..2dd2bc0cf4c3 100644
> > --- a/arch/x86/include/asm/kvm-x86-ops.h
> > +++ b/arch/x86/include/asm/kvm-x86-ops.h
> > @@ -130,6 +130,7 @@ KVM_X86_OP(vcpu_deliver_sipi_vector)
> >  KVM_X86_OP_OPTIONAL_RET0(vcpu_get_apicv_inhibit_reasons);
> >  KVM_X86_OP(alloc_apic_backing_page)
> >  KVM_X86_OP_OPTIONAL(rmp_page_level_adjust)
> > +KVM_X86_OP(update_protected_guest_state)
> >
> >  #undef KVM_X86_OP
> >  #undef KVM_X86_OP_OPTIONAL
> > diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
> > index 49b217dc8d7e..8abc0e724f5c 100644
> > --- a/arch/x86/include/asm/kvm_host.h
> > +++ b/arch/x86/include/asm/kvm_host.h
> > @@ -1522,7 +1522,10 @@ struct kvm_x86_ops {
> >         unsigned long (*vcpu_get_apicv_inhibit_reasons)(struct kvm_vcpu *vcpu);
> >
> >         void *(*alloc_apic_backing_page)(struct kvm_vcpu *vcpu);
> > +
> >         void (*rmp_page_level_adjust)(struct kvm *kvm, kvm_pfn_t pfn, int *level);
> > +
> > +       int (*update_protected_guest_state)(struct kvm_vcpu *vcpu);
> >  };
> >
> >  struct kvm_x86_nested_ops {
> > diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c
> > index cb2d1bbb862b..4ed90331bca0 100644
> > --- a/arch/x86/kvm/svm/sev.c
> > +++ b/arch/x86/kvm/svm/sev.c
> > @@ -341,6 +341,7 @@ static int sev_guest_init(struct kvm *kvm, struct kvm_sev_cmd *argp)
> >                 if (ret)
> >                         goto e_free;
> >
> > +               spin_lock_init(&sev->psc_lock);
> >                 ret = sev_snp_init(&argp->error);
> >         } else {
> >                 ret = sev_platform_init(&argp->error);
> > @@ -2828,19 +2829,28 @@ static inline int svm_map_ghcb(struct vcpu_svm *svm, struct kvm_host_map *map)
> >  {
> >         struct vmcb_control_area *control = &svm->vmcb->control;
> >         u64 gfn = gpa_to_gfn(control->ghcb_gpa);
> > +       struct kvm_vcpu *vcpu = &svm->vcpu;
> >
> > -       if (kvm_vcpu_map(&svm->vcpu, gfn, map)) {
> > +       if (kvm_vcpu_map(vcpu, gfn, map)) {
> >                 /* Unable to map GHCB from guest */
> >                 pr_err("error mapping GHCB GFN [%#llx] from guest\n", gfn);
> >                 return -EFAULT;
> >         }
> >
> > +       if (sev_post_map_gfn(vcpu->kvm, map->gfn, map->pfn)) {
> > +               kvm_vcpu_unmap(vcpu, map, false);
> > +               return -EBUSY;
> > +       }
> > +
> >         return 0;
> >  }
> >
> >  static inline void svm_unmap_ghcb(struct vcpu_svm *svm, struct kvm_host_map *map)
> >  {
> > -       kvm_vcpu_unmap(&svm->vcpu, map, true);
> > +       struct kvm_vcpu *vcpu = &svm->vcpu;
> > +
> > +       kvm_vcpu_unmap(vcpu, map, true);
> > +       sev_post_unmap_gfn(vcpu->kvm, map->gfn, map->pfn);
> >  }
> >
> >  static void dump_ghcb(struct vcpu_svm *svm)
> > @@ -3383,6 +3393,8 @@ static int __snp_handle_page_state_change(struct kvm_vcpu *vcpu, enum psc_op op,
> >                                 return PSC_UNDEF_ERR;
> >                 }
> >
> > +               spin_lock(&sev->psc_lock);
> > +
> >                 write_lock(&kvm->mmu_lock);
> >
> >                 rc = kvm_mmu_get_tdp_walk(vcpu, gpa, &pfn, &npt_level);
> > @@ -3417,6 +3429,8 @@ static int __snp_handle_page_state_change(struct kvm_vcpu *vcpu, enum psc_op op,
> >
> >                 write_unlock(&kvm->mmu_lock);
> >
> > +               spin_unlock(&sev->psc_lock);
>
> There is a corner case where the psc_lock is not released. If
> kvm_mmu_get_tdp_walk fails, the lock will be kept and will cause soft
> lockup.
>
> > +
> >                 if (rc) {
> >                         pr_err_ratelimited("Error op %d gpa %llx pfn %llx level %d rc %d\n",
> >                                            op, gpa, pfn, level, rc);
> > @@ -3965,3 +3979,33 @@ void sev_rmp_page_level_adjust(struct kvm *kvm, kvm_pfn_t pfn, int *level)
> >         /* Adjust the level to keep the NPT and RMP in sync */
> >         *level = min_t(size_t, *level, rmp_level);
> >  }
> > +
> > +int sev_post_map_gfn(struct kvm *kvm, gfn_t gfn, kvm_pfn_t pfn)
> > +{
> > +       struct kvm_sev_info *sev = &to_kvm_svm(kvm)->sev_info;
> > +       int level;
> > +
> > +       if (!sev_snp_guest(kvm))
> > +               return 0;
> > +
> > +       spin_lock(&sev->psc_lock);
> > +
> > +       /* If pfn is not added as private then fail */
> > +       if (snp_lookup_rmpentry(pfn, &level) == 1) {
> > +               spin_unlock(&sev->psc_lock);
> > +               pr_err_ratelimited("failed to map private gfn 0x%llx pfn 0x%llx\n", gfn, pfn);
> > +               return -EBUSY;
> > +       }
> > +
> > +       return 0;
> > +}
> > +
> > +void sev_post_unmap_gfn(struct kvm *kvm, gfn_t gfn, kvm_pfn_t pfn)
> > +{
> > +       struct kvm_sev_info *sev = &to_kvm_svm(kvm)->sev_info;
> > +
> > +       if (!sev_snp_guest(kvm))
> > +               return;
> > +
> > +       spin_unlock(&sev->psc_lock);
> > +}
> > diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
> > index b24e0171cbf2..1c8e035ba011 100644
> > --- a/arch/x86/kvm/svm/svm.c
> > +++ b/arch/x86/kvm/svm/svm.c
> > @@ -4734,7 +4734,10 @@ static struct kvm_x86_ops svm_x86_ops __initdata = {
> >         .vcpu_get_apicv_inhibit_reasons = avic_vcpu_get_apicv_inhibit_reasons,
> >
> >         .alloc_apic_backing_page = svm_alloc_apic_backing_page,
> > +
> >         .rmp_page_level_adjust = sev_rmp_page_level_adjust,
> > +
> > +       .update_protected_guest_state = sev_snp_update_protected_guest_state,
> >  };

I don't see this function sev_snp_update_protected_guest_state() being
defined anywhere in this series.

Then this line is removed in 'KVM: SVM: Support SEV-SNP AP Creation
NAE event'. Should this line just be removed from this patch in the
first place?

> >
> >  /*
> > diff --git a/arch/x86/kvm/svm/svm.h b/arch/x86/kvm/svm/svm.h
> > index 54ff56cb6125..3fd95193ed8d 100644
> > --- a/arch/x86/kvm/svm/svm.h
> > +++ b/arch/x86/kvm/svm/svm.h
> > @@ -79,19 +79,25 @@ struct kvm_sev_info {
> >         bool active;            /* SEV enabled guest */
> >         bool es_active;         /* SEV-ES enabled guest */
> >         bool snp_active;        /* SEV-SNP enabled guest */
> > +
> >         unsigned int asid;      /* ASID used for this guest */
> >         unsigned int handle;    /* SEV firmware handle */
> >         int fd;                 /* SEV device fd */
> > +
> >         unsigned long pages_locked; /* Number of pages locked */
> >         struct list_head regions_list;  /* List of registered regions */
> > +
> >         u64 ap_jump_table;      /* SEV-ES AP Jump Table address */
> > +
> >         struct kvm *enc_context_owner; /* Owner of copied encryption context */
> >         struct list_head mirror_vms; /* List of VMs mirroring */
> >         struct list_head mirror_entry; /* Use as a list entry of mirrors */
> >         struct misc_cg *misc_cg; /* For misc cgroup accounting */
> >         atomic_t migration_in_progress;
> > +
> >         u64 snp_init_flags;
> >         void *snp_context;      /* SNP guest context page */
> > +       spinlock_t psc_lock;
> >  };
> >
> >  struct kvm_svm {
> > @@ -702,6 +708,11 @@ void sev_es_prepare_switch_to_guest(struct sev_es_save_area *hostsa);
> >  void sev_es_unmap_ghcb(struct vcpu_svm *svm);
> >  struct page *snp_safe_alloc_page(struct kvm_vcpu *vcpu);
> >  void sev_rmp_page_level_adjust(struct kvm *kvm, kvm_pfn_t pfn, int *level);
> > +int sev_post_map_gfn(struct kvm *kvm, gfn_t gfn, kvm_pfn_t pfn);
> > +void sev_post_unmap_gfn(struct kvm *kvm, gfn_t gfn, kvm_pfn_t pfn);
> > +void handle_rmp_page_fault(struct kvm_vcpu *vcpu, gpa_t gpa, u64 error_code);
> > +void sev_snp_init_protected_guest_state(struct kvm_vcpu *vcpu);
> > +int sev_snp_update_protected_guest_state(struct kvm_vcpu *vcpu);

Ditto should this be removed?

> >
> >  /* vmenter.S */
> >
> > --
> > 2.25.1
> >