[PATCH 09/14] KVM: arm64: nv: Handle VNCR_EL2-triggered faults

Marc Zyngier
2025-02-15T15:02:03Z

As VNCR_EL2.BADDR contains a VA, it is bound to trigger faults.

These faults can have multiple source:

- We haven't mapped anything on the host: we need to compute the
resulting translation, populate a TLB, and eventually map
the corresponding page

- The permissions are out of whack: we need to tell the guest about
this state of affairs

Note that the kernel doesn't support S1POE for itself yet, so
the particular case of a VNCR page mapped with no permissions
or with write-only permissions is not correctly handled yet.

Signed-off-by: Marc Zyngier <maz@kernel.org>
---
arch/arm64/include/asm/esr.h | 2 +
arch/arm64/include/asm/kvm_host.h | 1 +
arch/arm64/include/asm/kvm_nested.h | 1 +
arch/arm64/kvm/handle_exit.c | 1 +
arch/arm64/kvm/nested.c | 158 ++++++++++++++++++++++++++++
5 files changed, 163 insertions(+)

diff --git a/arch/arm64/include/asm/esr.h b/arch/arm64/include/asm/esr.h
index d1b1a33f9a8b0..011d29c017b9e 100644
--- a/arch/arm64/include/asm/esr.h
+++ b/arch/arm64/include/asm/esr.h
@@ -99,6 +99,8 @@
#define ESR_ELx_AET_CE (UL(6) << ESR_ELx_AET_SHIFT)

/* Shared ISS field definitions for Data/Instruction aborts */
+#define ESR_ELx_VNCR_SHIFT (13)
+#define ESR_ELx_VNCR (UL(1) << ESR_ELx_VNCR_SHIFT)
#define ESR_ELx_SET_SHIFT (11)
#define ESR_ELx_SET_MASK (UL(3) << ESR_ELx_SET_SHIFT)
#define ESR_ELx_FnV_SHIFT (10)
diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
index 9b91a9e97cdce..3cccf6fca4dfa 100644
--- a/arch/arm64/include/asm/kvm_host.h
+++ b/arch/arm64/include/asm/kvm_host.h
@@ -52,6 +52,7 @@
#define KVM_REQ_SUSPEND KVM_ARCH_REQ(6)
#define KVM_REQ_RESYNC_PMU_EL0 KVM_ARCH_REQ(7)
#define KVM_REQ_NESTED_S2_UNMAP KVM_ARCH_REQ(8)
+#define KVM_REQ_MAP_L1_VNCR_EL2 KVM_ARCH_REQ(9)

#define KVM_DIRTY_LOG_MANUAL_CAPS (KVM_DIRTY_LOG_MANUAL_PROTECT_ENABLE | \
KVM_DIRTY_LOG_INITIALLY_SET)
diff --git a/arch/arm64/include/asm/kvm_nested.h b/arch/arm64/include/asm/kvm_nested.h
index 6a168ae95aef4..53ff314b9ecd1 100644
--- a/arch/arm64/include/asm/kvm_nested.h
+++ b/arch/arm64/include/asm/kvm_nested.h
@@ -334,5 +334,6 @@ int __kvm_translate_va(struct kvm_vcpu *vcpu, struct s1_walk_info *wi,

/* VNCR management */
int kvm_vcpu_allocate_vncr_tlb(struct kvm_vcpu *vcpu);
+int kvm_handle_vncr_abort(struct kvm_vcpu *vcpu);

#endif /* __ARM64_KVM_NESTED_H */
diff --git a/arch/arm64/kvm/handle_exit.c b/arch/arm64/kvm/handle_exit.c
index 512d152233ff2..e89132673630d 100644
--- a/arch/arm64/kvm/handle_exit.c
+++ b/arch/arm64/kvm/handle_exit.c
@@ -313,6 +313,7 @@ static exit_handle_fn arm_exit_handlers[] = {
[ESR_ELx_EC_ERET] = kvm_handle_eret,
[ESR_ELx_EC_IABT_LOW] = kvm_handle_guest_abort,
[ESR_ELx_EC_DABT_LOW] = kvm_handle_guest_abort,
+ [ESR_ELx_EC_DABT_CUR] = kvm_handle_vncr_abort,
[ESR_ELx_EC_SOFTSTP_LOW]= kvm_handle_guest_debug,
[ESR_ELx_EC_WATCHPT_LOW]= kvm_handle_guest_debug,
[ESR_ELx_EC_BREAKPT_LOW]= kvm_handle_guest_debug,
diff --git a/arch/arm64/kvm/nested.c b/arch/arm64/kvm/nested.c
index aed25a003750d..2c4991a84e003 100644
--- a/arch/arm64/kvm/nested.c
+++ b/arch/arm64/kvm/nested.c
@@ -881,6 +881,164 @@ int kvm_vcpu_allocate_vncr_tlb(struct kvm_vcpu *vcpu)
return 0;
}

+static u64 read_vncr_el2(struct kvm_vcpu *vcpu)
+{
+ return (u64)sign_extend64(__vcpu_sys_reg(vcpu, VNCR_EL2), 48);
+}
+
+static int kvm_translate_vncr(struct kvm_vcpu *vcpu)
+{
+ bool write_fault, writable;
+ unsigned long mmu_seq;
+ struct vncr_tlb *vt;
+ struct page *page;
+ u64 va, pfn, gfn;
+ int ret;
+
+ vt = vcpu->arch.vncr_tlb;
+
+ vt->wi = (struct s1_walk_info) {
+ .regime = TR_EL20,
+ .as_el0 = false,
+ .pan = false,
+ };
+ vt->wr = (struct s1_walk_result){};
+ vt->valid = false;
+
+ guard(srcu)(&vcpu->kvm->srcu);
+
+ va = read_vncr_el2(vcpu);
+
+ ret = __kvm_translate_va(vcpu, &vt->wi, &vt->wr, va);
+ if (ret)
+ return ret;
+
+ write_fault = kvm_is_write_fault(vcpu);
+
+ mmu_seq = vcpu->kvm->mmu_invalidate_seq;
+ smp_rmb();
+
+ gfn = vt->wr.pa >> PAGE_SHIFT;
+ pfn = kvm_faultin_pfn(vcpu, gfn, write_fault, &writable, &page);
+ if (is_error_noslot_pfn(pfn) || (write_fault && !writable))
+ return -EFAULT;
+
+ scoped_guard(write_lock, &vcpu->kvm->mmu_lock) {
+ if (mmu_invalidate_retry(vcpu->kvm, mmu_seq))
+ return -EAGAIN;
+
+ vt->gva = va;
+ vt->hpa = pfn << PAGE_SHIFT;
+ vt->valid = true;
+ vt->cpu = -1;
+
+ kvm_make_request(KVM_REQ_MAP_L1_VNCR_EL2, vcpu);
+ }
+
+ kvm_release_faultin_page(vcpu->kvm, page, false, vt->wr.pw);
+ if (vt->wr.pw)
+ mark_page_dirty(vcpu->kvm, gfn);
+
+ return 0;
+}
+
+static void inject_vncr_perm(struct kvm_vcpu *vcpu)
+{
+ struct vncr_tlb *vt = vcpu->arch.vncr_tlb;
+ u64 esr = kvm_vcpu_get_esr(vcpu);
+
+ /* Adjust the fault level to reflect that of the guest's */
+ esr &= ~ESR_ELx_FSC;
+ esr |= FIELD_PREP(ESR_ELx_FSC,
+ ESR_ELx_FSC_PERM_L(vt->wr.level));
+
+ kvm_inject_nested_sync(vcpu, esr);
+}
+
+static bool kvm_vncr_tlb_lookup(struct kvm_vcpu *vcpu)
+{
+ struct vncr_tlb *vt = vcpu->arch.vncr_tlb;
+
+ lockdep_assert_held_read(&vcpu->kvm->mmu_lock);
+
+ if (!vt->valid)
+ return false;
+
+ if (read_vncr_el2(vcpu) != vt->gva)
+ return false;
+
+ if (vt->wr.nG) {
+ u64 tcr = vcpu_read_sys_reg(vcpu, TCR_EL2);
+ u64 ttbr = ((tcr & TCR_A1) ?
+ vcpu_read_sys_reg(vcpu, TTBR1_EL2) :
+ vcpu_read_sys_reg(vcpu, TTBR0_EL2));
+ u16 asid;
+
+ asid = FIELD_GET(TTBR_ASID_MASK, ttbr);
+ if (!kvm_has_feat_enum(vcpu->kvm, ID_AA64MMFR0_EL1, ASIDBITS, 16) ||
+ !(tcr & TCR_ASID16))
+ asid &= GENMASK(7, 0);
+
+ return asid != vt->wr.asid;
+ }
+
+ return true;
+}
+
+int kvm_handle_vncr_abort(struct kvm_vcpu *vcpu)
+{
+ struct vncr_tlb *vt = vcpu->arch.vncr_tlb;
+ u64 esr = kvm_vcpu_get_esr(vcpu);
+
+ BUG_ON(!(esr & ESR_ELx_VNCR_SHIFT));
+
+ if (esr_fsc_is_permission_fault(esr)) {
+ inject_vncr_perm(vcpu);
+ } else if (esr_fsc_is_translation_fault(esr)) {
+ bool valid;
+ int ret;
+
+ scoped_guard(read_lock, &vcpu->kvm->mmu_lock)
+ valid = kvm_vncr_tlb_lookup(vcpu);
+
+ if (!valid)
+ ret = kvm_translate_vncr(vcpu);
+ else
+ ret = -EPERM;
+
+ switch (ret) {
+ case -EAGAIN:
+ case -ENOMEM:
+ /* Let's try again... */
+ break;
+ case -EFAULT:
+ case -EINVAL:
+ case -ENOENT:
+ /*
+ * Translation failed, inject the corresponding
+ * exception back to EL2.
+ */
+ BUG_ON(!vt->wr.failed);
+
+ esr &= ~ESR_ELx_FSC;
+ esr |= FIELD_PREP(ESR_ELx_FSC, vt->wr.fst);
+
+ kvm_inject_nested_sync(vcpu, esr);
+ break;
+ case -EPERM:
+ /* Hack to deal with POE until we get kernel support */
+ inject_vncr_perm(vcpu);
+ break;
+ case 0:
+ break;
+ }
+ } else {
+ WARN_ONCE(1, "Unhandled VNCR abort, ESR=%llx\n", esr);
+ }
+
+ return 1;
+}
+
/*
* Our emulated CPU doesn't support all the possible features. For the
* sake of simplicity (and probably mental sanity), wipe out a number
--
2.39.2