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Subject[RFC 47/55] KVM: arm/arm64: Forward the guest hypervisor's stage 2 permission faults
Date
From: Christoffer Dall <christoffer.dall@linaro.org>

When faulting on a shadow stage 2 page table we have to check if the
fault was a permission fault and if so, if that fault needs to be
handled by the guest hypervisor before us, in case the guest hypervisor
has created a less permissive S2 entry than the operation required.

Check if this is the case, and inject a fault if it is.

Signed-off-by: Christoffer Dall <christoffer.dall@linaro.org>
Signed-off-by: Jintack Lim <jintack@cs.columbia.edu>
---
arch/arm/include/asm/kvm_mmu.h | 7 +++++++
arch/arm/kvm/mmu.c | 5 +++++
arch/arm64/include/asm/kvm_mmu.h | 9 +++++++++
arch/arm64/kvm/mmu-nested.c | 33 +++++++++++++++++++++++++++++++++
4 files changed, 54 insertions(+)

diff --git a/arch/arm/include/asm/kvm_mmu.h b/arch/arm/include/asm/kvm_mmu.h
index ab41a10..0d106ae 100644
--- a/arch/arm/include/asm/kvm_mmu.h
+++ b/arch/arm/include/asm/kvm_mmu.h
@@ -241,6 +241,13 @@ static inline int kvm_walk_nested_s2(struct kvm_vcpu *vcpu, phys_addr_t gipa,
return 0;
}

+static inline int kvm_s2_handle_perm_fault(struct kvm_vcpu *vcpu,
+ phys_addr_t fault_ipa,
+ struct kvm_s2_trans *trans)
+{
+ return 0;
+}
+
static inline void kvm_nested_s2_unmap(struct kvm_vcpu *vcpu) { }
static inline int kvm_nested_s2_init(struct kvm_vcpu *vcpu) { return 0; }
static inline void kvm_nested_s2_teardown(struct kvm_vcpu *vcpu) { }
diff --git a/arch/arm/kvm/mmu.c b/arch/arm/kvm/mmu.c
index abdf345..68fc8e8 100644
--- a/arch/arm/kvm/mmu.c
+++ b/arch/arm/kvm/mmu.c
@@ -1542,6 +1542,11 @@ int kvm_handle_guest_abort(struct kvm_vcpu *vcpu, struct kvm_run *run)
ret = kvm_walk_nested_s2(vcpu, fault_ipa, &nested_trans);
if (ret)
goto out_unlock;
+
+ ret = kvm_s2_handle_perm_fault(vcpu, fault_ipa, &nested_trans);
+ if (ret)
+ goto out_unlock;
+
ipa = nested_trans.output;
}

diff --git a/arch/arm64/include/asm/kvm_mmu.h b/arch/arm64/include/asm/kvm_mmu.h
index 2ac603d..2086296 100644
--- a/arch/arm64/include/asm/kvm_mmu.h
+++ b/arch/arm64/include/asm/kvm_mmu.h
@@ -338,6 +338,8 @@ struct kvm_s2_trans {
bool handle_vttbr_update(struct kvm_vcpu *vcpu, u64 vttbr);
int kvm_walk_nested_s2(struct kvm_vcpu *vcpu, phys_addr_t gipa,
struct kvm_s2_trans *result);
+int kvm_s2_handle_perm_fault(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
+ struct kvm_s2_trans *trans);
void kvm_nested_s2_unmap(struct kvm_vcpu *vcpu);
int kvm_nested_s2_init(struct kvm_vcpu *vcpu);
void kvm_nested_s2_teardown(struct kvm_vcpu *vcpu);
@@ -366,6 +368,13 @@ static inline int kvm_walk_nested_s2(struct kvm_vcpu *vcpu, phys_addr_t gipa,
return 0;
}

+static inline int kvm_s2_handle_perm_fault(struct kvm_vcpu *vcpu,
+ phys_addr_t fault_ipa,
+ struct kvm_s2_trans *trans)
+{
+ return 0;
+}
+
static inline void kvm_nested_s2_unmap(struct kvm_vcpu *vcpu) { }
static inline int kvm_nested_s2_init(struct kvm_vcpu *vcpu) { return 0; }
static inline void kvm_nested_s2_teardown(struct kvm_vcpu *vcpu) { }
diff --git a/arch/arm64/kvm/mmu-nested.c b/arch/arm64/kvm/mmu-nested.c
index b579d23..65ad0da 100644
--- a/arch/arm64/kvm/mmu-nested.c
+++ b/arch/arm64/kvm/mmu-nested.c
@@ -52,6 +52,19 @@ static unsigned int pa_max(void)
return ps_to_output_size(parange);
}

+static int vcpu_inject_s2_perm_fault(struct kvm_vcpu *vcpu, gpa_t ipa,
+ int level)
+{
+ u32 esr;
+
+ vcpu->arch.ctxt.el2_regs[FAR_EL2] = vcpu->arch.fault.far_el2;
+ vcpu->arch.ctxt.el2_regs[HPFAR_EL2] = vcpu->arch.fault.hpfar_el2;
+ esr = kvm_vcpu_get_hsr(vcpu) & ~ESR_ELx_FSC;
+ esr |= ESR_ELx_FSC_PERM;
+ esr |= level & 0x3;
+ return kvm_inject_nested_sync(vcpu, esr);
+}
+
static int vcpu_inject_s2_trans_fault(struct kvm_vcpu *vcpu, gpa_t ipa,
int level)
{
@@ -268,6 +281,26 @@ int kvm_walk_nested_s2(struct kvm_vcpu *vcpu, phys_addr_t gipa,
return walk_nested_s2_pgd(vcpu, gipa, &wi, result);
}

+/*
+ * Returns non-zero if permission fault is handled by injecting it to the next
+ * level hypervisor.
+ */
+int kvm_s2_handle_perm_fault(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
+ struct kvm_s2_trans *trans)
+{
+ unsigned long fault_status = kvm_vcpu_trap_get_fault_type(vcpu);
+ bool write_fault = kvm_is_write_fault(vcpu);
+
+ if (fault_status != FSC_PERM)
+ return 0;
+
+ if ((write_fault && !trans->writable) ||
+ (!write_fault && !trans->readable))
+ return vcpu_inject_s2_perm_fault(vcpu, fault_ipa, trans->level);
+
+ return 0;
+}
+
/* expects kvm->mmu_lock to be held */
void kvm_nested_s2_all_vcpus_wp(struct kvm *kvm)
{
--
1.9.1

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