[PATCH 0/8] KVM: arm64: Add KVM_PRE_FAULT_MEMORY support

[PATCH 0/8] KVM: arm64: Add KVM_PRE_FAULT_MEMORY support

[Lorenzo Stoakes (ARM)]

This series implements the KVM stage 2 page table pre-faulting feature for
arm64.

== Foundations ==

The series begins by establishing required foundations:

1. Updating kvm_s2_fault_desc to independently store the exception syndrome
   register (ESR) value, and updating all code paths to use this value
   exclusively.

This is needed so we can later generate a synthetic fault to perform the
pre-faulting - we need to be sure the code doesn't grab an incorrect ESR
from elsewhere.

2. Updating kvm_s2_fault_desc to independently store the kvm_s2_mmu and
   updating all code paths to use this value exclusively.

Similarly this is needed so we can generate a synthetic fault against the
canonical stage 2 MMU (it would make no sense for it to touch nested shadow
page tables) - we need to be sure that the code doesn't grab an incorrect
MMU from elsewhere.

3. Updating the abort paths which consume kvm_s2_fault_desc to also return
   a kvm_s2_fault_result data structure.

To perform pre-faulting the code must know the granule size of what was
just walked. So the abort paths have to tell us what that was.

4. Pass walk flags to kvm_pgtable_get_leaf() to permit walking page tables
   under the MMU read lock.

This is Jack's patch, verbatim, which allows the use of the
KVM_PGTABLE_WALK_SHARED flag to walk page tables under the MMU read lock.

Pre-faulting requires it to be able to work in parallel as specified by the
API. The read lock precludes page tables being torn down behind our back.

== Implementation ==

Pre-faulting is implemented in kvm_arch_vcpu_pre_fault_memory() whose job
is to pre-fault the stage 2 page tables which map a specific GPA (which,
for arm64, is the guest's IPA).

This function is called by kvm_vcpu_pre_fault_memory() for each GPA in the
range, which itself is ultimately invoked by userland via the
KVM_PRE_FAULT_MEMORY ioctl.

The implementation is simple - try to walk to the stage 2 page table
mapping the GPA - if unmapped, fault it in through a synthetic page fault.

pKVM is not supported regardless of whether the VM is protected or
not.

This is because pKVM instantiates vCPUs upon run, but pre-faulting is
typically performed before a vCPU is run. It would be confusing and
inconsistent to error out on non-running vCPUs but to pre-fault running
ones.

Jack's original test suite is also included in the series.

== Credits ==

This series is based, with gratitude, on Jack Thomson's series and their
respins (links provided below) as well as the feedback he received.

The series includes Jack's v5 "KVM: arm64: Pass walk flags to
kvm_pgtable_get_leaf()" patch verbatim, and all three of his test patches,
two of which required minor fixups.

Link: https://patch.msgid.link/20260612162354.73378-1-jackabt.amazon@gmail.com/
Link: https://patch.msgid.link/20260113152643.18858-1-jackabt.amazon@gmail.com/
Link: https://patch.msgid.link/20251119154910.97716-1-jackabt.amazon@gmail.com/
Link: https://patch.msgid.link/20251013151502.6679-1-jackabt.amazon@gmail.com/
Link: https://patch.msgid.link/20250911134648.58945-1-jackabt.amazon@gmail.com/

== Reviewer Notes ==

I synced with maintainers on this who asked me to take a look, as there hadn't
been progress on the series for some time.

Am happy to rebase again after -rc1.

Signed-off-by: Lorenzo Stoakes (ARM) <ljs@kernel.org>
---
Jack Thomson (4):
      KVM: arm64: Pass walk flags to kvm_pgtable_get_leaf()
      KVM: selftests: Enable pre_fault_memory_test for arm64
      KVM: selftests: Add option for different backing in pre-fault tests
      KVM: selftests: Add nested pre-fault test for arm64

Lorenzo Stoakes (ARM) (4):
      KVM: arm64: Propagate and use esr in s2fd when handling guest aborts
      KVM: arm64: Propagate and use mmu in s2fd when handling guest aborts
      KVM: arm64: Propagate and use kvm_s2_fault_result on S2 fault
      KVM: arm64: Implement KVM_PRE_FAULT_MEMORY

 Documentation/virt/kvm/api.rst                     |  17 +-
 arch/arm64/include/asm/esr.h                       | 129 +++++---
 arch/arm64/include/asm/kvm_emulate.h               |  52 +---
 arch/arm64/include/asm/kvm_pgtable.h               |   5 +-
 arch/arm64/include/asm/kvm_pkvm.h                  |   2 +-
 arch/arm64/kvm/Kconfig                             |   1 +
 arch/arm64/kvm/arm.c                               |   1 +
 arch/arm64/kvm/hyp/nvhe/mem_protect.c              |  10 +-
 arch/arm64/kvm/hyp/pgtable.c                       |   5 +-
 arch/arm64/kvm/mmu.c                               | 324 +++++++++++++++++----
 arch/arm64/kvm/nested.c                            |   2 +-
 tools/testing/selftests/kvm/Makefile.kvm           |   2 +
 .../selftests/kvm/arm64/nv_pre_fault_memory_test.c | 206 +++++++++++++
 .../testing/selftests/kvm/pre_fault_memory_test.c  | 152 ++++++++--
 14 files changed, 736 insertions(+), 172 deletions(-)
---
base-commit: aa8e5dc6a7a2a1141ab40706a51010adcd0e57d2
change-id: 20260815-kvm-arm-prefault-9bb411b6897d

Best regards,
-- 
Lorenzo Stoakes (ARM) <ljs@kernel.org>

[PATCH 1/8] KVM: arm64: Propagate and use esr in s2fd when handling guest aborts

[Lorenzo Stoakes (ARM)]

kvm_handle_guest_abort() establishes a kvm_s2_fault_desc data structure,
s2fd, to store and propagate state to either pkvm_mem_abort(), gmem_abort()
or user_mem_abort() handlers.

Each of these, however, examines the Exception Syndrome Register (ESR) via
s2fd->vcpu.

Introduce an s2fd->esr field to abstract this and propagate it to callers.

The value of this (beyond refactoring) is to be able to later generate
faults with a synthetic esr, specifically to implement stage 2 page table
pre-faulting.

Abstract esr-specific predicates and helpers to the esr.h header and either
have vcpu wrappers call these, or eliminate them if they are not used
elsewhere.

Provide kvm_s2_fault_is_[write,exec,perm]() helpers for convenience.

Since kvm_s2_fault_map() either sets perm_fault_granule to the permission
fault granule or 0 if not a permission fault, implement
kvm_s2_perm_fault_granule() to do this directly.

Abort handlers which use kvm_s2_fault_desc - gmem_abort() and
user_mem_abort() - now only reference s2fd->esr and do not look it up in
any other way, which makes it safe to pass a synthetic s2fd->esr value to
these functions.

No functional change intended.

Signed-off-by: Lorenzo Stoakes (ARM) <ljs@kernel.org>
---
 arch/arm64/include/asm/esr.h         | 129 +++++++++++++++++++++++++----------
 arch/arm64/include/asm/kvm_emulate.h |  52 ++++----------
 arch/arm64/kvm/mmu.c                 |  80 +++++++++++++---------
 3 files changed, 156 insertions(+), 105 deletions(-)

diff --git a/arch/arm64/include/asm/esr.h b/arch/arm64/include/asm/esr.h
index f816f5d77f1a..162e90c832e9 100644
--- a/arch/arm64/include/asm/esr.h
+++ b/arch/arm64/include/asm/esr.h
@@ -437,6 +437,32 @@
 #ifndef __ASSEMBLER__
 #include <asm/types.h>
 
+static inline u8 esr_trap_get_class(unsigned long esr)
+{
+	return ESR_ELx_EC(esr);
+}
+
+static inline bool esr_trap_is_iabt(unsigned long esr)
+{
+	return esr_trap_get_class(esr) == ESR_ELx_EC_IABT_LOW;
+}
+
+static inline bool esr_abt_is_s1ptw(unsigned long esr)
+{
+	return esr & ESR_ELx_S1PTW;
+}
+
+/* Always check for S1PTW *before* using this. */
+static inline bool esr_dabt_is_write(unsigned long esr)
+{
+	return esr & ESR_ELx_WNR;
+}
+
+static inline bool esr_dabt_is_cm(unsigned long esr)
+{
+	return esr & ESR_ELx_CM;
+}
+
 static inline unsigned long esr_brk_comment(unsigned long esr)
 {
 	return esr & ESR_ELx_BRK64_ISS_COMMENT_MASK;
@@ -460,75 +486,104 @@ static inline bool esr_is_ubsan_brk(unsigned long esr)
 	return (esr_brk_comment(esr) & ~UBSAN_BRK_MASK) == UBSAN_BRK_IMM;
 }
 
+static inline u8 esr_fsc_get_fault(unsigned long esr)
+{
+	return esr & ESR_ELx_FSC;
+}
+
 static inline bool esr_fsc_is_translation_fault(unsigned long esr)
 {
-	esr = esr & ESR_ELx_FSC;
+	const u8 fault = esr_fsc_get_fault(esr);
 
-	return (esr == ESR_ELx_FSC_FAULT_L(3)) ||
-	       (esr == ESR_ELx_FSC_FAULT_L(2)) ||
-	       (esr == ESR_ELx_FSC_FAULT_L(1)) ||
-	       (esr == ESR_ELx_FSC_FAULT_L(0)) ||
-	       (esr == ESR_ELx_FSC_FAULT_L(-1));
+	return (fault == ESR_ELx_FSC_FAULT_L(3)) ||
+	       (fault == ESR_ELx_FSC_FAULT_L(2)) ||
+	       (fault == ESR_ELx_FSC_FAULT_L(1)) ||
+	       (fault == ESR_ELx_FSC_FAULT_L(0)) ||
+	       (fault == ESR_ELx_FSC_FAULT_L(-1));
 }
 
 static inline bool esr_fsc_is_permission_fault(unsigned long esr)
 {
-	esr = esr & ESR_ELx_FSC;
+	const u8 fault = esr_fsc_get_fault(esr);
 
-	return (esr == ESR_ELx_FSC_PERM_L(3)) ||
-	       (esr == ESR_ELx_FSC_PERM_L(2)) ||
-	       (esr == ESR_ELx_FSC_PERM_L(1)) ||
-	       (esr == ESR_ELx_FSC_PERM_L(0));
+	return (fault == ESR_ELx_FSC_PERM_L(3)) ||
+	       (fault == ESR_ELx_FSC_PERM_L(2)) ||
+	       (fault == ESR_ELx_FSC_PERM_L(1)) ||
+	       (fault == ESR_ELx_FSC_PERM_L(0));
 }
 
 static inline bool esr_fsc_is_access_flag_fault(unsigned long esr)
 {
-	esr = esr & ESR_ELx_FSC;
+	const u8 fault = esr_fsc_get_fault(esr);
 
-	return (esr == ESR_ELx_FSC_ACCESS_L(3)) ||
-	       (esr == ESR_ELx_FSC_ACCESS_L(2)) ||
-	       (esr == ESR_ELx_FSC_ACCESS_L(1)) ||
-	       (esr == ESR_ELx_FSC_ACCESS_L(0));
+	return (fault == ESR_ELx_FSC_ACCESS_L(3)) ||
+	       (fault == ESR_ELx_FSC_ACCESS_L(2)) ||
+	       (fault == ESR_ELx_FSC_ACCESS_L(1)) ||
+	       (fault == ESR_ELx_FSC_ACCESS_L(0));
 }
 
 static inline bool esr_fsc_is_excl_atomic_fault(unsigned long esr)
 {
-	esr = esr & ESR_ELx_FSC;
-
-	return esr == ESR_ELx_FSC_EXCL_ATOMIC;
+	return esr_fsc_get_fault(esr) == ESR_ELx_FSC_EXCL_ATOMIC;
 }
 
 static inline bool esr_fsc_is_addr_sz_fault(unsigned long esr)
 {
-	esr &= ESR_ELx_FSC;
+	const u8 fault = esr_fsc_get_fault(esr);
+
+	return (fault == ESR_ELx_FSC_ADDRSZ_L(3)) ||
+	       (fault == ESR_ELx_FSC_ADDRSZ_L(2)) ||
+	       (fault == ESR_ELx_FSC_ADDRSZ_L(1)) ||
+	       (fault == ESR_ELx_FSC_ADDRSZ_L(0)) ||
+	       (fault == ESR_ELx_FSC_ADDRSZ_L(-1));
+}
+
+static inline bool esr_abt_is_exec_fault(unsigned long esr)
+{
+	return esr_trap_is_iabt(esr) && !esr_abt_is_s1ptw(esr);
+}
 
-	return (esr == ESR_ELx_FSC_ADDRSZ_L(3))	||
-	       (esr == ESR_ELx_FSC_ADDRSZ_L(2))	||
-	       (esr == ESR_ELx_FSC_ADDRSZ_L(1)) ||
-	       (esr == ESR_ELx_FSC_ADDRSZ_L(0))	||
-	       (esr == ESR_ELx_FSC_ADDRSZ_L(-1));
+static inline bool esr_abt_is_sea(unsigned long esr)
+{
+	const u8 fault = esr_fsc_get_fault(esr);
+
+	switch (fault) {
+	case ESR_ELx_FSC_EXTABT:
+	case ESR_ELx_FSC_SEA_TTW(-1) ... ESR_ELx_FSC_SEA_TTW(3):
+	case ESR_ELx_FSC_SECC:
+	case ESR_ELx_FSC_SECC_TTW(-1) ... ESR_ELx_FSC_SECC_TTW(3):
+		return true;
+	default:
+		return false;
+	}
+}
+
+/* Not valid for negative levels. */
+static inline u64 esr_fsc_get_level(unsigned long esr)
+{
+	return esr & ESR_ELx_FSC_LEVEL;
 }
 
 static inline bool esr_fsc_is_sea_ttw(unsigned long esr)
 {
-	esr = esr & ESR_ELx_FSC;
+	const u8 fault = esr_fsc_get_fault(esr);
 
-	return (esr == ESR_ELx_FSC_SEA_TTW(3)) ||
-	       (esr == ESR_ELx_FSC_SEA_TTW(2)) ||
-	       (esr == ESR_ELx_FSC_SEA_TTW(1)) ||
-	       (esr == ESR_ELx_FSC_SEA_TTW(0)) ||
-	       (esr == ESR_ELx_FSC_SEA_TTW(-1));
+	return (fault == ESR_ELx_FSC_SEA_TTW(3)) ||
+	       (fault == ESR_ELx_FSC_SEA_TTW(2)) ||
+	       (fault == ESR_ELx_FSC_SEA_TTW(1)) ||
+	       (fault == ESR_ELx_FSC_SEA_TTW(0)) ||
+	       (fault == ESR_ELx_FSC_SEA_TTW(-1));
 }
 
 static inline bool esr_fsc_is_secc_ttw(unsigned long esr)
 {
-	esr = esr & ESR_ELx_FSC;
+	const u8 fault = esr_fsc_get_fault(esr);
 
-	return (esr == ESR_ELx_FSC_SECC_TTW(3)) ||
-	       (esr == ESR_ELx_FSC_SECC_TTW(2)) ||
-	       (esr == ESR_ELx_FSC_SECC_TTW(1)) ||
-	       (esr == ESR_ELx_FSC_SECC_TTW(0)) ||
-	       (esr == ESR_ELx_FSC_SECC_TTW(-1));
+	return (fault == ESR_ELx_FSC_SECC_TTW(3)) ||
+	       (fault == ESR_ELx_FSC_SECC_TTW(2)) ||
+	       (fault == ESR_ELx_FSC_SECC_TTW(1)) ||
+	       (fault == ESR_ELx_FSC_SECC_TTW(0)) ||
+	       (fault == ESR_ELx_FSC_SECC_TTW(-1));
 }
 
 /* Indicate whether ESR.EC==0x1A is for an ERETAx instruction */
diff --git a/arch/arm64/include/asm/kvm_emulate.h b/arch/arm64/include/asm/kvm_emulate.h
index a3c1928bdf74..811d7a68a9f9 100644
--- a/arch/arm64/include/asm/kvm_emulate.h
+++ b/arch/arm64/include/asm/kvm_emulate.h
@@ -411,18 +411,13 @@ static __always_inline int kvm_vcpu_dabt_get_rd(const struct kvm_vcpu *vcpu)
 
 static __always_inline bool kvm_vcpu_abt_iss1tw(const struct kvm_vcpu *vcpu)
 {
-	return !!(kvm_vcpu_get_esr(vcpu) & ESR_ELx_S1PTW);
+	return esr_abt_is_s1ptw(kvm_vcpu_get_esr(vcpu));
 }
 
 /* Always check for S1PTW *before* using this. */
 static __always_inline bool kvm_vcpu_dabt_iswrite(const struct kvm_vcpu *vcpu)
 {
-	return kvm_vcpu_get_esr(vcpu) & ESR_ELx_WNR;
-}
-
-static inline bool kvm_vcpu_dabt_is_cm(const struct kvm_vcpu *vcpu)
-{
-	return !!(kvm_vcpu_get_esr(vcpu) & ESR_ELx_CM);
+	return esr_dabt_is_write(kvm_vcpu_get_esr(vcpu));
 }
 
 static __always_inline unsigned int kvm_vcpu_dabt_get_as(const struct kvm_vcpu *vcpu)
@@ -438,17 +433,12 @@ static __always_inline bool kvm_vcpu_trap_il_is32bit(const struct kvm_vcpu *vcpu
 
 static __always_inline u8 kvm_vcpu_trap_get_class(const struct kvm_vcpu *vcpu)
 {
-	return ESR_ELx_EC(kvm_vcpu_get_esr(vcpu));
+	return esr_trap_get_class(kvm_vcpu_get_esr(vcpu));
 }
 
 static inline bool kvm_vcpu_trap_is_iabt(const struct kvm_vcpu *vcpu)
 {
-	return kvm_vcpu_trap_get_class(vcpu) == ESR_ELx_EC_IABT_LOW;
-}
-
-static inline bool kvm_vcpu_trap_is_exec_fault(const struct kvm_vcpu *vcpu)
-{
-	return kvm_vcpu_trap_is_iabt(vcpu) && !kvm_vcpu_abt_iss1tw(vcpu);
+	return esr_trap_is_iabt(kvm_vcpu_get_esr(vcpu));
 }
 
 static __always_inline u8 kvm_vcpu_trap_get_fault(const struct kvm_vcpu *vcpu)
@@ -468,26 +458,9 @@ bool kvm_vcpu_trap_is_translation_fault(const struct kvm_vcpu *vcpu)
 	return esr_fsc_is_translation_fault(kvm_vcpu_get_esr(vcpu));
 }
 
-static inline
-u64 kvm_vcpu_trap_get_perm_fault_granule(const struct kvm_vcpu *vcpu)
-{
-	unsigned long esr = kvm_vcpu_get_esr(vcpu);
-
-	BUG_ON(!esr_fsc_is_permission_fault(esr));
-	return BIT(ARM64_HW_PGTABLE_LEVEL_SHIFT(esr & ESR_ELx_FSC_LEVEL));
-}
-
 static __always_inline bool kvm_vcpu_abt_issea(const struct kvm_vcpu *vcpu)
 {
-	switch (kvm_vcpu_trap_get_fault(vcpu)) {
-	case ESR_ELx_FSC_EXTABT:
-	case ESR_ELx_FSC_SEA_TTW(-1) ... ESR_ELx_FSC_SEA_TTW(3):
-	case ESR_ELx_FSC_SECC:
-	case ESR_ELx_FSC_SECC_TTW(-1) ... ESR_ELx_FSC_SECC_TTW(3):
-		return true;
-	default:
-		return false;
-	}
+	return esr_abt_is_sea(kvm_vcpu_get_esr(vcpu));
 }
 
 static __always_inline int kvm_vcpu_sys_get_rt(struct kvm_vcpu *vcpu)
@@ -496,9 +469,9 @@ static __always_inline int kvm_vcpu_sys_get_rt(struct kvm_vcpu *vcpu)
 	return ESR_ELx_SYS64_ISS_RT(esr);
 }
 
-static inline bool kvm_is_write_fault(struct kvm_vcpu *vcpu)
+static inline bool esr_abt_is_write_fault(unsigned long esr)
 {
-	if (kvm_vcpu_abt_iss1tw(vcpu)) {
+	if (esr_abt_is_s1ptw(esr)) {
 		/*
 		 * Only a permission fault on a S1PTW should be
 		 * considered as a write. Otherwise, page tables baked
@@ -511,13 +484,18 @@ static inline bool kvm_is_write_fault(struct kvm_vcpu *vcpu)
 		 * first), then a permission fault to allow the flags
 		 * to be set.
 		 */
-		return kvm_vcpu_trap_is_permission_fault(vcpu);
+		return esr_fsc_is_permission_fault(esr);
 	}
 
-	if (kvm_vcpu_trap_is_iabt(vcpu))
+	if (esr_trap_is_iabt(esr))
 		return false;
 
-	return kvm_vcpu_dabt_iswrite(vcpu);
+	return esr_dabt_is_write(esr);
+}
+
+static inline bool kvm_is_write_fault(struct kvm_vcpu *vcpu)
+{
+	return esr_abt_is_write_fault(kvm_vcpu_get_esr(vcpu));
 }
 
 static inline unsigned long kvm_vcpu_get_mpidr_aff(struct kvm_vcpu *vcpu)
diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c
index 74e7e7f7564c..30d605e87b01 100644
--- a/arch/arm64/kvm/mmu.c
+++ b/arch/arm64/kvm/mmu.c
@@ -1603,12 +1603,38 @@ struct kvm_s2_fault_desc {
 	struct kvm_s2_trans	*nested;
 	struct kvm_memory_slot	*memslot;
 	unsigned long		hva;
+	unsigned long		esr;
 };
 
+static bool kvm_s2_fault_is_perm(const struct kvm_s2_fault_desc *s2fd)
+{
+	return esr_fsc_is_permission_fault(s2fd->esr);
+}
+
+static bool kvm_s2_fault_is_exec(const struct kvm_s2_fault_desc *s2fd)
+{
+	return esr_abt_is_exec_fault(s2fd->esr);
+}
+
+static bool kvm_s2_fault_is_write(const struct kvm_s2_fault_desc *s2fd)
+{
+	return esr_abt_is_write_fault(s2fd->esr);
+}
+
+static u64 kvm_s2_perm_fault_granule(const struct kvm_s2_fault_desc *s2fd)
+{
+	u64 level;
+
+	if (!kvm_s2_fault_is_perm(s2fd))
+		return 0;
+	level = esr_fsc_get_level(s2fd->esr);
+	return BIT(ARM64_HW_PGTABLE_LEVEL_SHIFT(level));
+}
+
 static int gmem_abort(const struct kvm_s2_fault_desc *s2fd)
 {
 	bool write_fault, exec_fault;
-	bool perm_fault = kvm_vcpu_trap_is_permission_fault(s2fd->vcpu);
+	const bool perm_fault = kvm_s2_fault_is_perm(s2fd);
 	enum kvm_pgtable_walk_flags flags = KVM_PGTABLE_WALK_SHARED;
 	enum kvm_pgtable_prot prot = KVM_PGTABLE_PROT_R;
 	struct kvm_pgtable *pgt = s2fd->vcpu->arch.hw_mmu->pgt;
@@ -1632,8 +1658,8 @@ static int gmem_abort(const struct kvm_s2_fault_desc *s2fd)
 	else
 		gfn = s2fd->fault_ipa >> PAGE_SHIFT;
 
-	write_fault = kvm_is_write_fault(s2fd->vcpu);
-	exec_fault = kvm_vcpu_trap_is_exec_fault(s2fd->vcpu);
+	write_fault = kvm_s2_fault_is_write(s2fd);
+	exec_fault = kvm_s2_fault_is_exec(s2fd);
 
 	VM_WARN_ON_ONCE(write_fault && exec_fault);
 
@@ -1840,11 +1866,6 @@ static short kvm_s2_resolve_vma_size(const struct kvm_s2_fault_desc *s2fd,
 	return vma_shift;
 }
 
-static bool kvm_s2_fault_is_perm(const struct kvm_s2_fault_desc *s2fd)
-{
-	return kvm_vcpu_trap_is_permission_fault(s2fd->vcpu);
-}
-
 static int kvm_s2_fault_get_vma_info(const struct kvm_s2_fault_desc *s2fd,
 				     struct kvm_s2_fault_vma_info *s2vi)
 {
@@ -1910,7 +1931,7 @@ static int kvm_s2_fault_pin_pfn(const struct kvm_s2_fault_desc *s2fd,
 		return ret;
 
 	s2vi->pfn = __kvm_faultin_pfn(s2fd->memslot, get_canonical_gfn(s2fd, s2vi),
-				      kvm_is_write_fault(s2fd->vcpu) ? FOLL_WRITE : 0,
+				      kvm_s2_fault_is_write(s2fd) ? FOLL_WRITE : 0,
 				      &s2vi->map_writable, &s2vi->page);
 	if (unlikely(is_error_noslot_pfn(s2vi->pfn))) {
 		if (s2vi->pfn == KVM_PFN_ERR_HWPOISON) {
@@ -1968,7 +1989,7 @@ static int kvm_s2_fault_compute_prot(const struct kvm_s2_fault_desc *s2fd,
 {
 	struct kvm *kvm = s2fd->vcpu->kvm;
 
-	if (kvm_vcpu_trap_is_exec_fault(s2fd->vcpu) && s2vi->map_non_cacheable)
+	if (kvm_s2_fault_is_exec(s2fd) && s2vi->map_non_cacheable)
 		return -ENOEXEC;
 
 	/*
@@ -1977,7 +1998,7 @@ static int kvm_s2_fault_compute_prot(const struct kvm_s2_fault_desc *s2fd,
 	 * and trigger the exception here. Since the memslot is valid, inject
 	 * the fault back to the guest.
 	 */
-	if (esr_fsc_is_excl_atomic_fault(kvm_vcpu_get_esr(s2fd->vcpu))) {
+	if (esr_fsc_is_excl_atomic_fault(s2fd->esr)) {
 		kvm_inject_dabt_excl_atomic(s2fd->vcpu, kvm_vcpu_get_hfar(s2fd->vcpu));
 		return 1;
 	}
@@ -1986,13 +2007,13 @@ static int kvm_s2_fault_compute_prot(const struct kvm_s2_fault_desc *s2fd,
 
 	if (s2vi->map_writable && (s2vi->device ||
 				   !memslot_is_logging(s2fd->memslot) ||
-				   kvm_is_write_fault(s2fd->vcpu)))
+				   kvm_s2_fault_is_write(s2fd)))
 		*prot |= KVM_PGTABLE_PROT_W;
 
 	if (s2fd->nested)
 		*prot = adjust_nested_fault_perms(s2fd->nested, *prot);
 
-	if (kvm_vcpu_trap_is_exec_fault(s2fd->vcpu))
+	if (kvm_s2_fault_is_exec(s2fd))
 		*prot |= KVM_PGTABLE_PROT_X;
 
 	if (s2vi->map_non_cacheable)
@@ -2034,8 +2055,7 @@ static int kvm_s2_fault_map(const struct kvm_s2_fault_desc *s2fd,
 	if (mmu_invalidate_retry(kvm, s2vi->mmu_seq))
 		goto out_unlock;
 
-	perm_fault_granule = (kvm_s2_fault_is_perm(s2fd) ?
-			      kvm_vcpu_trap_get_perm_fault_granule(s2fd->vcpu) : 0);
+	perm_fault_granule = kvm_s2_perm_fault_granule(s2fd);
 	mapping_size = s2vi->vma_pagesize;
 	pfn = s2vi->pfn;
 	gfn = s2vi->gfn;
@@ -2103,7 +2123,7 @@ static int kvm_s2_fault_map(const struct kvm_s2_fault_desc *s2fd,
 
 static int user_mem_abort(const struct kvm_s2_fault_desc *s2fd)
 {
-	bool perm_fault = kvm_vcpu_trap_is_permission_fault(s2fd->vcpu);
+	const bool perm_fault = kvm_s2_fault_is_perm(s2fd);
 	struct kvm_s2_fault_vma_info s2vi = {};
 	enum kvm_pgtable_prot prot;
 	void *memcache;
@@ -2250,7 +2270,7 @@ int kvm_handle_guest_sea(struct kvm_vcpu *vcpu)
 int kvm_handle_guest_abort(struct kvm_vcpu *vcpu)
 {
 	struct kvm_s2_trans nested_trans, *nested = NULL;
-	unsigned long esr;
+	const unsigned long esr = kvm_vcpu_get_esr(vcpu);
 	phys_addr_t fault_ipa; /* The address we faulted on */
 	phys_addr_t ipa; /* Always the IPA in the L1 guest phys space */
 	struct kvm_memory_slot *memslot;
@@ -2259,11 +2279,9 @@ int kvm_handle_guest_abort(struct kvm_vcpu *vcpu)
 	gfn_t gfn;
 	int ret, idx;
 
-	if (kvm_vcpu_abt_issea(vcpu))
+	if (esr_abt_is_sea(esr))
 		return kvm_handle_guest_sea(vcpu);
 
-	esr = kvm_vcpu_get_esr(vcpu);
-
 	/*
 	 * The fault IPA should be reliable at this point as we're not dealing
 	 * with an SEA.
@@ -2272,7 +2290,7 @@ int kvm_handle_guest_abort(struct kvm_vcpu *vcpu)
 	if (KVM_BUG_ON(ipa == INVALID_GPA, vcpu->kvm))
 		return -EFAULT;
 
-	is_iabt = kvm_vcpu_trap_is_iabt(vcpu);
+	is_iabt = esr_trap_is_iabt(esr);
 
 	if (esr_fsc_is_translation_fault(esr)) {
 		/* Beyond sanitised PARange (which is the IPA limit) */
@@ -2289,7 +2307,7 @@ int kvm_handle_guest_abort(struct kvm_vcpu *vcpu)
 		}
 	}
 
-	trace_kvm_guest_fault(*vcpu_pc(vcpu), kvm_vcpu_get_esr(vcpu),
+	trace_kvm_guest_fault(*vcpu_pc(vcpu), esr,
 			      kvm_vcpu_get_hfar(vcpu), fault_ipa);
 
 	/* Check the stage-2 fault is trans. fault or write fault */
@@ -2298,9 +2316,9 @@ int kvm_handle_guest_abort(struct kvm_vcpu *vcpu)
 	    !esr_fsc_is_access_flag_fault(esr) &&
 	    !esr_fsc_is_excl_atomic_fault(esr)) {
 		kvm_err("Unsupported FSC: EC=%#x xFSC=%#lx ESR_EL2=%#lx\n",
-			kvm_vcpu_trap_get_class(vcpu),
-			(unsigned long)kvm_vcpu_trap_get_fault(vcpu),
-			(unsigned long)kvm_vcpu_get_esr(vcpu));
+			esr_trap_get_class(esr),
+			(unsigned long)esr_fsc_get_fault(esr),
+			(unsigned long)esr);
 		return -EFAULT;
 	}
 
@@ -2349,7 +2367,7 @@ int kvm_handle_guest_abort(struct kvm_vcpu *vcpu)
 	gfn = ipa >> PAGE_SHIFT;
 	memslot = gfn_to_memslot(vcpu->kvm, gfn);
 	hva = gfn_to_hva_memslot_prot(memslot, gfn, &writable);
-	write_fault = kvm_is_write_fault(vcpu);
+	write_fault = esr_abt_is_write_fault(esr);
 	if (kvm_is_error_hva(hva) || (write_fault && !writable)) {
 		/*
 		 * The guest has put either its instructions or its page-tables
@@ -2362,7 +2380,7 @@ int kvm_handle_guest_abort(struct kvm_vcpu *vcpu)
 			goto out;
 		}
 
-		if (kvm_vcpu_abt_iss1tw(vcpu)) {
+		if (esr_abt_is_s1ptw(esr)) {
 			ret = kvm_inject_sea_dabt(vcpu, kvm_vcpu_get_hfar(vcpu));
 			goto out_unlock;
 		}
@@ -2377,7 +2395,7 @@ int kvm_handle_guest_abort(struct kvm_vcpu *vcpu)
 		 * So let's assume that the guest is just being
 		 * cautious, and skip the instruction.
 		 */
-		if (kvm_is_error_hva(hva) && kvm_vcpu_dabt_is_cm(vcpu)) {
+		if (kvm_is_error_hva(hva) && esr_dabt_is_cm(esr)) {
 			kvm_incr_pc(vcpu);
 			ret = 1;
 			goto out_unlock;
@@ -2409,14 +2427,14 @@ int kvm_handle_guest_abort(struct kvm_vcpu *vcpu)
 		.nested		= nested,
 		.memslot	= memslot,
 		.hva		= hva,
+		.esr		= esr,
 	};
 
 	if (kvm_vm_is_protected(vcpu->kvm)) {
 		ret = pkvm_mem_abort(&s2fd);
 	} else {
-		VM_WARN_ON_ONCE(kvm_vcpu_trap_is_permission_fault(vcpu) &&
-				!write_fault &&
-				!kvm_vcpu_trap_is_exec_fault(vcpu));
+		VM_WARN_ON_ONCE(kvm_s2_fault_is_perm(&s2fd) && !write_fault &&
+				!kvm_s2_fault_is_exec(&s2fd));
 
 		if (kvm_slot_has_gmem(memslot))
 			ret = gmem_abort(&s2fd);

-- 
2.55.0

[PATCH 2/8] KVM: arm64: Propagate and use mmu in s2fd when handling guest aborts

[Lorenzo Stoakes (ARM)]

kvm_handle_guest_abort() establishes a kvm_s2_fault_desc data structure,
s2fd, to store and propagate state to either pkvm_mem_abort(), gmem_abort()
or user_mem_abort() handlers.

Each of these, however, examines the state of the stage 2 MMU via
vcpu->arch.hw_mmu.

Introduce an s2fd->mmu field to abstract this and propagate it to callers.

Similar to adding the esr field, this allows injection of synthetic faults
with the ultimate intention of implementing stage 2 page table
pre-faulting.

No functional change intended.

Signed-off-by: Lorenzo Stoakes (ARM) <ljs@kernel.org>
---
 arch/arm64/kvm/mmu.c | 17 ++++++++++-------
 1 file changed, 10 insertions(+), 7 deletions(-)

diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c
index 30d605e87b01..80cb520e25b9 100644
--- a/arch/arm64/kvm/mmu.c
+++ b/arch/arm64/kvm/mmu.c
@@ -1604,6 +1604,7 @@ struct kvm_s2_fault_desc {
 	struct kvm_memory_slot	*memslot;
 	unsigned long		hva;
 	unsigned long		esr;
+	struct kvm_s2_mmu	*mmu;
 };
 
 static bool kvm_s2_fault_is_perm(const struct kvm_s2_fault_desc *s2fd)
@@ -1637,7 +1638,7 @@ static int gmem_abort(const struct kvm_s2_fault_desc *s2fd)
 	const bool perm_fault = kvm_s2_fault_is_perm(s2fd);
 	enum kvm_pgtable_walk_flags flags = KVM_PGTABLE_WALK_SHARED;
 	enum kvm_pgtable_prot prot = KVM_PGTABLE_PROT_R;
-	struct kvm_pgtable *pgt = s2fd->vcpu->arch.hw_mmu->pgt;
+	struct kvm_pgtable *pgt = s2fd->mmu->pgt;
 	unsigned long mmu_seq;
 	struct page *page;
 	struct kvm *kvm = s2fd->vcpu->kvm;
@@ -1735,7 +1736,7 @@ static int pkvm_mem_abort(const struct kvm_s2_fault_desc *s2fd)
 {
 	unsigned int flags = FOLL_HWPOISON | FOLL_LONGTERM | FOLL_WRITE;
 	struct kvm_vcpu *vcpu = s2fd->vcpu;
-	struct kvm_pgtable *pgt = vcpu->arch.hw_mmu->pgt;
+	struct kvm_pgtable *pgt = s2fd->mmu->pgt;
 	struct mm_struct *mm = current->mm;
 	struct kvm *kvm = vcpu->kvm;
 	void *hyp_memcache;
@@ -2050,7 +2051,7 @@ static int kvm_s2_fault_map(const struct kvm_s2_fault_desc *s2fd,
 	int ret;
 
 	kvm_fault_lock(kvm);
-	pgt = s2fd->vcpu->arch.hw_mmu->pgt;
+	pgt = s2fd->mmu->pgt;
 	ret = -EAGAIN;
 	if (mmu_invalidate_retry(kvm, s2vi->mmu_seq))
 		goto out_unlock;
@@ -2271,6 +2272,7 @@ int kvm_handle_guest_abort(struct kvm_vcpu *vcpu)
 {
 	struct kvm_s2_trans nested_trans, *nested = NULL;
 	const unsigned long esr = kvm_vcpu_get_esr(vcpu);
+	struct kvm_s2_mmu *mmu = vcpu->arch.hw_mmu;
 	phys_addr_t fault_ipa; /* The address we faulted on */
 	phys_addr_t ipa; /* Always the IPA in the L1 guest phys space */
 	struct kvm_memory_slot *memslot;
@@ -2300,7 +2302,7 @@ int kvm_handle_guest_abort(struct kvm_vcpu *vcpu)
 		}
 
 		/* Falls between the IPA range and the PARange? */
-		if (fault_ipa >= BIT_ULL(VTCR_EL2_IPA(vcpu->arch.hw_mmu->vtcr))) {
+		if (fault_ipa >= BIT_ULL(VTCR_EL2_IPA(mmu->vtcr))) {
 			fault_ipa |= FAR_TO_FIPA_OFFSET(kvm_vcpu_get_hfar(vcpu));
 
 			return kvm_inject_sea(vcpu, is_iabt, fault_ipa);
@@ -2337,8 +2339,8 @@ int kvm_handle_guest_abort(struct kvm_vcpu *vcpu)
 	 * nothing to walk and we treat it as a 1:1 before going through the
 	 * canonical translation.
 	 */
-	if (kvm_is_nested_s2_mmu(vcpu->kvm,vcpu->arch.hw_mmu) &&
-	    vcpu->arch.hw_mmu->nested_stage2_enabled) {
+	if (kvm_is_nested_s2_mmu(vcpu->kvm, mmu) &&
+	    mmu->nested_stage2_enabled) {
 		u32 esr;
 
 		ret = kvm_walk_nested_s2(vcpu, fault_ipa, &nested_trans);
@@ -2413,7 +2415,7 @@ int kvm_handle_guest_abort(struct kvm_vcpu *vcpu)
 	}
 
 	/* Userspace should not be able to register out-of-bounds IPAs */
-	VM_BUG_ON(ipa >= kvm_phys_size(vcpu->arch.hw_mmu));
+	VM_BUG_ON(ipa >= kvm_phys_size(mmu));
 
 	if (esr_fsc_is_access_flag_fault(esr)) {
 		handle_access_fault(vcpu, fault_ipa);
@@ -2428,6 +2430,7 @@ int kvm_handle_guest_abort(struct kvm_vcpu *vcpu)
 		.memslot	= memslot,
 		.hva		= hva,
 		.esr		= esr,
+		.mmu		= mmu,
 	};
 
 	if (kvm_vm_is_protected(vcpu->kvm)) {

-- 
2.55.0

[PATCH 3/8] KVM: arm64: Propagate and use kvm_s2_fault_result on S2 fault

[Lorenzo Stoakes (ARM)]

When stage 2 page tables fault the net result may either be that a page is
mapped, an error occurred or the fault should be retried (-EAGAIN).

When a fault succeeds it may be upgraded to a PMD size via
transparent_hugepage_adjust().

In order to support KVM pre-faulting the outcome of the fault and the
mapping size must be recorded.

Track this in the new kvm_s2_fault_result struct, which is threaded through
gmem_abort(), user_mem_abort() and kvm_s2_fault_map().

PKVM and SEA aren't relevant to synthetic pre-faulting so neither
kvm_inject_sea() nor pkvm_mem_abort() are altered.

Actual hardware faulting doesn't require this information, so
kvm_handle_guest_abort() simply passes NULL kvm_s2_fault_result to
gmem_abort() and user_mem_abort().

Faults are necessarily ephemeral and pre-faulting can't guarantee what may
happen in parallel, so do not store the GFN or PFN in
kvm_s2_fault_result. Pre-faulting only needs to know what was mapped in at
the point of the fault.

This struct could be replaced with a pointer to an unsigned long, however
it's clearer to separate out the mapped flag and having a struct allows us
to easily add additional fields in future as needed.

No functional change intended.

Suggested-by: Vincent Donnefort <vdonnefort@google.com>
Signed-off-by: Lorenzo Stoakes (ARM) <ljs@kernel.org>
---
 arch/arm64/kvm/mmu.c | 33 +++++++++++++++++++++++++++------
 1 file changed, 27 insertions(+), 6 deletions(-)

diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c
index 80cb520e25b9..da15da4e40e6 100644
--- a/arch/arm64/kvm/mmu.c
+++ b/arch/arm64/kvm/mmu.c
@@ -1607,6 +1607,11 @@ struct kvm_s2_fault_desc {
 	struct kvm_s2_mmu	*mmu;
 };
 
+struct kvm_s2_fault_result {
+	unsigned long mapping_size;
+	bool mapped;
+};
+
 static bool kvm_s2_fault_is_perm(const struct kvm_s2_fault_desc *s2fd)
 {
 	return esr_fsc_is_permission_fault(s2fd->esr);
@@ -1632,7 +1637,17 @@ static u64 kvm_s2_perm_fault_granule(const struct kvm_s2_fault_desc *s2fd)
 	return BIT(ARM64_HW_PGTABLE_LEVEL_SHIFT(level));
 }
 
-static int gmem_abort(const struct kvm_s2_fault_desc *s2fd)
+static void populate_fault_result(struct kvm_s2_fault_result *result,
+				  unsigned long mapping_size)
+{
+	/* A THP upgrade may have altered mapping size. */
+	result->mapping_size = mapping_size;
+	/* -EAGAIN is swallowed so be explicit when we actually map. */
+	result->mapped = true;
+}
+
+static int gmem_abort(const struct kvm_s2_fault_desc *s2fd,
+		      struct kvm_s2_fault_result *result)
 {
 	bool write_fault, exec_fault;
 	const bool perm_fault = kvm_s2_fault_is_perm(s2fd);
@@ -1714,6 +1729,8 @@ static int gmem_abort(const struct kvm_s2_fault_desc *s2fd)
 	if ((prot & KVM_PGTABLE_PROT_W) && !ret)
 		mark_page_dirty_in_slot(kvm, s2fd->memslot, gfn);
 
+	if (result && !ret)
+		populate_fault_result(result, PAGE_SIZE);
 	return ret != -EAGAIN ? ret : 0;
 }
 
@@ -2038,7 +2055,8 @@ static int kvm_s2_fault_compute_prot(const struct kvm_s2_fault_desc *s2fd,
 static int kvm_s2_fault_map(const struct kvm_s2_fault_desc *s2fd,
 			    const struct kvm_s2_fault_vma_info *s2vi,
 			    enum kvm_pgtable_prot prot,
-			    void *memcache)
+			    void *memcache,
+			    struct kvm_s2_fault_result *result)
 {
 	enum kvm_pgtable_walk_flags flags = KVM_PGTABLE_WALK_SHARED;
 	bool writable = prot & KVM_PGTABLE_PROT_W;
@@ -2117,12 +2135,15 @@ static int kvm_s2_fault_map(const struct kvm_s2_fault_desc *s2fd,
 		mark_page_dirty_in_slot(kvm, s2fd->memslot, gpa_to_gfn(ipa));
 	}
 
+	if (result && !ret)
+		populate_fault_result(result, mapping_size);
 	if (ret != -EAGAIN)
 		return ret;
 	return 0;
 }
 
-static int user_mem_abort(const struct kvm_s2_fault_desc *s2fd)
+static int user_mem_abort(const struct kvm_s2_fault_desc *s2fd,
+			  struct kvm_s2_fault_result *result)
 {
 	const bool perm_fault = kvm_s2_fault_is_perm(s2fd);
 	struct kvm_s2_fault_vma_info s2vi = {};
@@ -2161,7 +2182,7 @@ static int user_mem_abort(const struct kvm_s2_fault_desc *s2fd)
 		return ret;
 	}
 
-	return kvm_s2_fault_map(s2fd, &s2vi, prot, memcache);
+	return kvm_s2_fault_map(s2fd, &s2vi, prot, memcache, result);
 }
 
 /* Resolve the access fault by making the page young again. */
@@ -2440,9 +2461,9 @@ int kvm_handle_guest_abort(struct kvm_vcpu *vcpu)
 				!kvm_s2_fault_is_exec(&s2fd));
 
 		if (kvm_slot_has_gmem(memslot))
-			ret = gmem_abort(&s2fd);
+			ret = gmem_abort(&s2fd, NULL);
 		else
-			ret = user_mem_abort(&s2fd);
+			ret = user_mem_abort(&s2fd, NULL);
 	}
 
 	if (ret == 0)

-- 
2.55.0

[PATCH 4/8] KVM: arm64: Pass walk flags to kvm_pgtable_get_leaf()

[Lorenzo Stoakes (ARM)]

From: Jack Thomson <jackabt@amazon.com>

Allow callers of kvm_pgtable_get_leaf() to specify the page-table walk
flags, in preparation for performing walks under the MMU read lock.

Reading a stage-2 leaf while only holding the read lock requires
KVM_PGTABLE_WALK_SHARED: parallel faults (which also only hold the read
lock) can unlink table pages and free them via RCU, so the walker must
be inside an RCU read-side critical section, which the shared walk flag
provides via kvm_pgtable_walk_begin().

All existing callers either hold the write lock, walk with interrupts
disabled, or run at hyp where shared walks are rejected; they keep the
current behaviour by passing no flags.

No functional change intended.

Signed-off-by: Jack Thomson <jackabt@amazon.com>
Signed-off-by: Lorenzo Stoakes (ARM) <ljs@kernel.org>
---
 arch/arm64/include/asm/kvm_pgtable.h  |  5 ++++-
 arch/arm64/kvm/hyp/nvhe/mem_protect.c | 10 +++++-----
 arch/arm64/kvm/hyp/pgtable.c          |  5 +++--
 arch/arm64/kvm/mmu.c                  |  2 +-
 arch/arm64/kvm/nested.c               |  2 +-
 5 files changed, 14 insertions(+), 10 deletions(-)

diff --git a/arch/arm64/include/asm/kvm_pgtable.h b/arch/arm64/include/asm/kvm_pgtable.h
index 41a8687938eb..d0167f7dfbee 100644
--- a/arch/arm64/include/asm/kvm_pgtable.h
+++ b/arch/arm64/include/asm/kvm_pgtable.h
@@ -859,6 +859,8 @@ int kvm_pgtable_walk(struct kvm_pgtable *pgt, u64 addr, u64 size,
  * @addr:	Input address for the start of the walk.
  * @ptep:	Pointer to storage for the retrieved PTE.
  * @level:	Pointer to storage for the level of the retrieved PTE.
+ * @flags:	Flags to control the page-table walk
+ *		(see struct kvm_pgtable_visit_ctx).
  *
  * The offset of @addr within a page is ignored.
  *
@@ -869,7 +871,8 @@ int kvm_pgtable_walk(struct kvm_pgtable *pgt, u64 addr, u64 size,
  * Return: 0 on success, negative error code on failure.
  */
 int kvm_pgtable_get_leaf(struct kvm_pgtable *pgt, u64 addr,
-			 kvm_pte_t *ptep, s8 *level);
+			 kvm_pte_t *ptep, s8 *level,
+			 enum kvm_pgtable_walk_flags flags);
 
 /**
  * kvm_pgtable_stage2_pte_prot() - Retrieve the protection attributes of a
diff --git a/arch/arm64/kvm/hyp/nvhe/mem_protect.c b/arch/arm64/kvm/hyp/nvhe/mem_protect.c
index 39aa8911f62c..23a57312b981 100644
--- a/arch/arm64/kvm/hyp/nvhe/mem_protect.c
+++ b/arch/arm64/kvm/hyp/nvhe/mem_protect.c
@@ -532,7 +532,7 @@ static int host_stage2_adjust_range(u64 addr, struct kvm_mem_range *range)
 	int ret;
 
 	hyp_assert_lock_held(&host_mmu.lock);
-	ret = kvm_pgtable_get_leaf(&host_mmu.pgt, addr, &pte, &level);
+	ret = kvm_pgtable_get_leaf(&host_mmu.pgt, addr, &pte, &level, 0);
 	if (ret)
 		return ret;
 
@@ -910,7 +910,7 @@ static int get_valid_guest_pte(struct pkvm_hyp_vm *vm, u64 ipa, kvm_pte_t *ptep,
 	s8 level;
 	int ret;
 
-	ret = kvm_pgtable_get_leaf(&vm->pgt, ipa, &pte, &level);
+	ret = kvm_pgtable_get_leaf(&vm->pgt, ipa, &pte, &level, 0);
 	if (ret)
 		return ret;
 	if (guest_pte_is_poisoned(pte))
@@ -959,7 +959,7 @@ int __pkvm_vcpu_in_poison_fault(struct pkvm_hyp_vcpu *hyp_vcpu)
 	ipa |= FAR_TO_FIPA_OFFSET(kvm_vcpu_get_hfar(&hyp_vcpu->vcpu));
 
 	guest_lock_component(vm);
-	ret = kvm_pgtable_get_leaf(&vm->pgt, ipa, &pte, &level);
+	ret = kvm_pgtable_get_leaf(&vm->pgt, ipa, &pte, &level, 0);
 	if (ret)
 		goto unlock;
 
@@ -1315,7 +1315,7 @@ static int host_stage2_get_guest_info(phys_addr_t phys, struct pkvm_hyp_vm **vm,
 		return -EPERM;
 	}
 
-	ret = kvm_pgtable_get_leaf(&host_mmu.pgt, phys, &pte, &level);
+	ret = kvm_pgtable_get_leaf(&host_mmu.pgt, phys, &pte, &level, 0);
 	if (ret)
 		return ret;
 
@@ -1544,7 +1544,7 @@ static int __check_host_shared_guest(struct pkvm_hyp_vm *vm, u64 *__phys, u64 ip
 	s8 level;
 	int ret;
 
-	ret = kvm_pgtable_get_leaf(&vm->pgt, ipa, &pte, &level);
+	ret = kvm_pgtable_get_leaf(&vm->pgt, ipa, &pte, &level, 0);
 	if (ret)
 		return ret;
 	if (!kvm_pte_valid(pte))
diff --git a/arch/arm64/kvm/hyp/pgtable.c b/arch/arm64/kvm/hyp/pgtable.c
index b74dd5ce1efd..347eec3957d6 100644
--- a/arch/arm64/kvm/hyp/pgtable.c
+++ b/arch/arm64/kvm/hyp/pgtable.c
@@ -298,12 +298,13 @@ static int leaf_walker(const struct kvm_pgtable_visit_ctx *ctx,
 }
 
 int kvm_pgtable_get_leaf(struct kvm_pgtable *pgt, u64 addr,
-			 kvm_pte_t *ptep, s8 *level)
+			 kvm_pte_t *ptep, s8 *level,
+			 enum kvm_pgtable_walk_flags flags)
 {
 	struct leaf_walk_data data;
 	struct kvm_pgtable_walker walker = {
 		.cb	= leaf_walker,
-		.flags	= KVM_PGTABLE_WALK_LEAF,
+		.flags	= flags | KVM_PGTABLE_WALK_LEAF,
 		.arg	= &data,
 	};
 	int ret;
diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c
index da15da4e40e6..16299004f229 100644
--- a/arch/arm64/kvm/mmu.c
+++ b/arch/arm64/kvm/mmu.c
@@ -866,7 +866,7 @@ static int get_user_mapping_size(struct kvm *kvm, u64 addr)
 	 * IPI-ing threads).
 	 */
 	local_irq_save(flags);
-	ret = kvm_pgtable_get_leaf(&pgt, addr, &pte, &level);
+	ret = kvm_pgtable_get_leaf(&pgt, addr, &pte, &level, 0);
 	local_irq_restore(flags);
 
 	if (ret)
diff --git a/arch/arm64/kvm/nested.c b/arch/arm64/kvm/nested.c
index 17123f0b6dab..3488d5ad225b 100644
--- a/arch/arm64/kvm/nested.c
+++ b/arch/arm64/kvm/nested.c
@@ -654,7 +654,7 @@ static u8 get_guest_mapping_ttl(struct kvm_s2_mmu *mmu, u64 addr)
 		return 0;
 
 	tmp &= ~(sz - 1);
-	if (kvm_pgtable_get_leaf(mmu->pgt, tmp, &pte, NULL))
+	if (kvm_pgtable_get_leaf(mmu->pgt, tmp, &pte, NULL, 0))
 		goto again;
 	if (!(pte & PTE_VALID))
 		goto again;

-- 
2.55.0

[PATCH 5/8] KVM: arm64: Implement KVM_PRE_FAULT_MEMORY

[Lorenzo Stoakes (ARM)]

Implement KVM stage 2 page table pre-faulting for the arm64 architecture.

Do the trivial plumbing by selecting CONFIG_KVM_GENERIC_PRE_FAULT_MEMORY in
Kconfig, returning 1 in kvm_vm_ioctl_check_extension() for
KVM_CAP_PRE_FAULT_MEMORY but false in kvm_pkvm_ext_allowed() to disallow
its use for pKVM.

Add kvm_arch_vcpu_pre_fault_memory() to actually implement the feature by
pre-faulting stage 2 page tables for a specific GPA.

Previous commits added the required foundations - gmem_abort() and
user_mem_abort() determine esr and mmu from s2fd->esr and s2fd->mmu
respectively, the granule size is returned by them in kvm_s2_fault_result
and kvm_pgtable_get_leaf() accepts a walk flags parameter.

Additionally, kvm_pgtable_get_leaf() now accepts a walk flag, meaning its
page table walk can be performed with KVM_PGTABLE_WALK_SHARED set and thus
can be performed under a read mmu_lock.

With these changes in place, implement pre-faulting by first trying a page
table walk under the MMU read lock then, if it fails, injecting a
synthetic data abort at the page table level at which the page table walk
failed.

This is necessarily racey as reclaim might happen at any time. Successfully
pre-faulting can therefore only guarantee that each GPA was observed to be
mapped at least once.

Protected KVM (pKVM) is not supported at all because pKVM creates VMs and
vCPUs when first run, meaning any attempt to pre-fault prior to this cannot
succeed.

Since the sensible use case for pre-faulting is doing so prior to vCPU run,
and supporting only online pKVM vCPUs is confusing and inconsistent, simply
don't support this at all.

There is a subtlety when retrieving the hva: it seems natural to use
gfn_to_hva_memslot(), but this errors out for read-only memslots.

Since pre-faulting should fault in both read-only and read/write hvas, this
isn't the correct API to use here.

gfn_to_hva_memslot_prot() allows retrieval of read-only hvas, but has
unclear semantics, so introduce gfn_to_hva_memslot_read() to wrap it.

A retry mechanic is implemented when user_mem_abort() or gmem_abort() fail
to map memory due to a benign failure where a hardware abort would not
result in an error.

These occur when the abort handler was raced by either an invalidation MMU
notifier or a racing abort path.

Since these faults are highly likely to succeed on immediate retry, retry
up to MAX_PRE_FAULT_RETRIES times, after which -EAGAIN is ultimately
returned to the caller.

An invalid memslot (i.e. a memslot with the KVM_MEMSLOT_INVALID flag set)
also results in the operation returning -EAGAIN without a retry mechanic.

This is because an invalid memslot means the pre-fault operation raced with
memslot reclaim, and since the SRCU lock is held, progress cannot be made.

Therefore, when this happens, -EAGAIN indicates that userland should retry
the ioctl, which will bounce the SRCU lock and permit forward progress.

Finally, update the KVM API documentation to describe the changes,
providing arm64-specific implementation details.

This work is based with gratitude on Jack Thomson's original series, its
previous revisions and the feedback they received.

Link: https://patch.msgid.link/20260612162354.73378-1-jackabt.amazon@gmail.com/
Signed-off-by: Lorenzo Stoakes (ARM) <ljs@kernel.org>
---
 Documentation/virt/kvm/api.rst    |  17 +++-
 arch/arm64/include/asm/kvm_pkvm.h |   2 +-
 arch/arm64/kvm/Kconfig            |   1 +
 arch/arm64/kvm/arm.c              |   1 +
 arch/arm64/kvm/mmu.c              | 192 +++++++++++++++++++++++++++++++++++---
 5 files changed, 198 insertions(+), 15 deletions(-)

diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst
index 4988c32df4bf..6246f4a56bb9 100644
--- a/Documentation/virt/kvm/api.rst
+++ b/Documentation/virt/kvm/api.rst
@@ -6485,7 +6485,7 @@ See KVM_SET_USER_MEMORY_REGION2 for additional details.
 ---------------------------
 
 :Capability: KVM_CAP_PRE_FAULT_MEMORY
-:Architectures: none
+:Architectures: x86, s390, arm64
 :Type: vcpu ioctl
 :Parameters: struct kvm_pre_fault_memory (in/out)
 :Returns: 0 if at least one page is processed, < 0 on error
@@ -6493,12 +6493,14 @@ See KVM_SET_USER_MEMORY_REGION2 for additional details.
 Errors:
 
   ========== ===============================================================
+  EAGAIN     A race occurred before progress was made, but a retry may succeed.
   EINVAL     The specified `gpa` and `size` were invalid (e.g. not
              page aligned, causes an overflow, or size is zero), or the VM
              is UCONTROL (s390).
   ENOENT     The specified `gpa` is outside defined memslots.
   EINTR      An unmasked signal is pending and no page was processed.
   EFAULT     The parameter address was invalid.
+  EHWPOISON  A poisoned host page was encountered.
   EOPNOTSUPP Mapping memory for a GPA is unsupported by the
              hypervisor, and/or for the current vCPU state/mode.
   EIO        unexpected error conditions (also causes a WARN)
@@ -6518,7 +6520,16 @@ Errors:
 KVM_PRE_FAULT_MEMORY populates KVM's stage-2 page tables used to map memory
 for the current vCPU state.  KVM maps memory as if the vCPU generated a
 stage-2 read page fault, e.g. faults in memory as needed, but doesn't break
-CoW.  On x86, KVM does not mark any newly created stage-2 PTE as Accessed.
+CoW.  On arm64, KVM marks both existing and newly created stage-2 PTEs as
+Accessed, on x86 it does not and for s390 it is not applicable.
+
+On arm64, a GPA is interpreted as an IPA, and never interpreted as the IPA
+of a nested guest. Pre-faulting only populates canonical stage 2 page
+tables.
+
+The feature is not supported on arm64 if the protected KVM (pKVM) feature
+is enabled, as that results in vCPUs being instantiated on first run, which
+renders pre-faulting useless.
 
 In the case of confidential VM types where there is an initial set up of
 private guest memory before the guest is 'finalized'/measured, this ioctl
@@ -6533,7 +6544,7 @@ When the ioctl returns, the input values are updated to point to the
 remaining range.  If `size` > 0 on return, the caller can just issue
 the ioctl again with the same `struct kvm_map_memory` argument.
 
-Shadow page tables cannot support this ioctl because they
+On x86, Shadow page tables cannot support this ioctl because they
 are indexed by virtual address or nested guest physical address.
 Calling this ioctl when the guest is using shadow page tables (for
 example because it is running a nested guest with nested page tables)
diff --git a/arch/arm64/include/asm/kvm_pkvm.h b/arch/arm64/include/asm/kvm_pkvm.h
index beea00e693a0..4d6e5765e9e5 100644
--- a/arch/arm64/include/asm/kvm_pkvm.h
+++ b/arch/arm64/include/asm/kvm_pkvm.h
@@ -44,9 +44,9 @@ static inline bool kvm_pkvm_ext_allowed(struct kvm *kvm, long ext)
 	case KVM_CAP_ARM_PTRAUTH_GENERIC:
 		return true;
 	case KVM_CAP_ARM_MTE:
-		return false;
 	case KVM_CAP_ARM_EAGER_SPLIT_CHUNK_SIZE:
 	case KVM_CAP_ARM_SUPPORTED_BLOCK_SIZES:
+	case KVM_CAP_PRE_FAULT_MEMORY:
 		return false;
 	default:
 		return !kvm || !kvm_vm_is_protected(kvm);
diff --git a/arch/arm64/kvm/Kconfig b/arch/arm64/kvm/Kconfig
index 449154f9a485..71233068b7cb 100644
--- a/arch/arm64/kvm/Kconfig
+++ b/arch/arm64/kvm/Kconfig
@@ -37,6 +37,7 @@ menuconfig KVM
 	select SCHED_INFO
 	select GUEST_PERF_EVENTS if PERF_EVENTS
 	select KVM_GUEST_MEMFD
+	select KVM_GENERIC_PRE_FAULT_MEMORY
 	help
 	  Support hosting virtualized guest machines.
 
diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c
index ccae82c1242b..58ac70f31d84 100644
--- a/arch/arm64/kvm/arm.c
+++ b/arch/arm64/kvm/arm.c
@@ -393,6 +393,7 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
 	case KVM_CAP_COUNTER_OFFSET:
 	case KVM_CAP_ARM_WRITABLE_IMP_ID_REGS:
 	case KVM_CAP_ARM_SEA_TO_USER:
+	case KVM_CAP_PRE_FAULT_MEMORY:
 		r = 1;
 		break;
 	case KVM_CAP_SET_GUEST_DEBUG2:
diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c
index 16299004f229..401ae538ae75 100644
--- a/arch/arm64/kvm/mmu.c
+++ b/arch/arm64/kvm/mmu.c
@@ -5,6 +5,7 @@
  */
 
 #include <linux/acpi.h>
+#include <linux/cleanup.h>
 #include <linux/mman.h>
 #include <linux/kvm_host.h>
 #include <linux/io.h>
@@ -1554,9 +1555,9 @@ static void *get_mmu_memcache(struct kvm_vcpu *vcpu)
 		return &vcpu->arch.pkvm_memcache;
 }
 
-static int topup_mmu_memcache(struct kvm_vcpu *vcpu, void *memcache)
+static int topup_mmu_memcache(struct kvm_s2_mmu *mmu, void *memcache)
 {
-	int min_pages = kvm_mmu_cache_min_pages(vcpu->arch.hw_mmu);
+	const int min_pages = kvm_mmu_cache_min_pages(mmu);
 
 	if (!is_protected_kvm_enabled())
 		return kvm_mmu_topup_memory_cache(memcache, min_pages);
@@ -1605,6 +1606,7 @@ struct kvm_s2_fault_desc {
 	unsigned long		hva;
 	unsigned long		esr;
 	struct kvm_s2_mmu	*mmu;
+	bool			pre_fault;
 };
 
 struct kvm_s2_fault_result {
@@ -1664,7 +1666,7 @@ static int gmem_abort(const struct kvm_s2_fault_desc *s2fd,
 
 	if (!perm_fault) {
 		memcache = get_mmu_memcache(s2fd->vcpu);
-		ret = topup_mmu_memcache(s2fd->vcpu, memcache);
+		ret = topup_mmu_memcache(s2fd->mmu, memcache);
 		if (ret)
 			return ret;
 	}
@@ -1761,7 +1763,7 @@ static int pkvm_mem_abort(const struct kvm_s2_fault_desc *s2fd)
 	int ret;
 
 	hyp_memcache = get_mmu_memcache(vcpu);
-	ret = topup_mmu_memcache(vcpu, hyp_memcache);
+	ret = topup_mmu_memcache(s2fd->mmu, hyp_memcache);
 	if (ret)
 		return -ENOMEM;
 
@@ -1953,6 +1955,8 @@ static int kvm_s2_fault_pin_pfn(const struct kvm_s2_fault_desc *s2fd,
 				      &s2vi->map_writable, &s2vi->page);
 	if (unlikely(is_error_noslot_pfn(s2vi->pfn))) {
 		if (s2vi->pfn == KVM_PFN_ERR_HWPOISON) {
+			if (s2fd->pre_fault)
+				return -EHWPOISON;
 			kvm_send_hwpoison_signal(s2fd->hva, __ffs(s2vi->vma_pagesize));
 			return 0;
 		}
@@ -2163,7 +2167,7 @@ static int user_mem_abort(const struct kvm_s2_fault_desc *s2fd,
 	memcache = get_mmu_memcache(s2fd->vcpu);
 	if (!perm_fault || memslot_is_logging(s2fd->memslot) ||
 	    is_protected_kvm_enabled()) {
-		ret = topup_mmu_memcache(s2fd->vcpu, memcache);
+		ret = topup_mmu_memcache(s2fd->mmu, memcache);
 		if (ret)
 			return ret;
 	}
@@ -2185,18 +2189,22 @@ static int user_mem_abort(const struct kvm_s2_fault_desc *s2fd,
 	return kvm_s2_fault_map(s2fd, &s2vi, prot, memcache, result);
 }
 
-/* Resolve the access fault by making the page young again. */
-static void handle_access_fault(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa)
+static void __handle_access_fault(struct kvm_pgtable *pgt, phys_addr_t fault_ipa)
 {
 	enum kvm_pgtable_walk_flags flags = KVM_PGTABLE_WALK_SHARED;
-	struct kvm_s2_mmu *mmu;
 
 	trace_kvm_access_fault(fault_ipa);
+	KVM_PGT_FN(kvm_pgtable_stage2_mkyoung)(pgt, fault_ipa, flags);
+}
+
+/* Resolve the access fault by making the page young again. */
+static void handle_access_fault(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa)
+{
+	struct kvm_s2_mmu *mmu;
 
-	read_lock(&vcpu->kvm->mmu_lock);
+	guard(read_lock)(&vcpu->kvm->mmu_lock);
 	mmu = vcpu->arch.hw_mmu;
-	KVM_PGT_FN(kvm_pgtable_stage2_mkyoung)(mmu->pgt, fault_ipa, flags);
-	read_unlock(&vcpu->kvm->mmu_lock);
+	__handle_access_fault(mmu->pgt, fault_ipa);
 }
 
 /*
@@ -2834,3 +2842,165 @@ void kvm_toggle_cache(struct kvm_vcpu *vcpu, bool was_enabled)
 
 	trace_kvm_toggle_cache(*vcpu_pc(vcpu), was_enabled, now_enabled);
 }
+
+static bool kvm_pte_young_s2(kvm_pte_t pte)
+{
+	return pte & KVM_PTE_LEAF_ATTR_LO_S2_AF;
+}
+
+static void kvm_pte_mkyoung_s2(struct kvm_pgtable *pgt, gpa_t gpa)
+{
+	struct kvm *kvm = kvm_s2_mmu_to_kvm(pgt->mmu);
+
+	lockdep_assert_held(&kvm->mmu_lock);
+	/* Despite its name, doesn't fault here. */
+	__handle_access_fault(pgt, gpa);
+}
+
+/*
+ * Try to walk to the specified GPA in canonical mmu - if unmapped returns 0, if
+ * mapped returns the granule size, otherwise returns an error.
+ */
+static long kvm_walk_s2(struct kvm_pgtable *pgt,
+			gpa_t gpa, s8 *level)
+{
+	struct kvm *kvm = kvm_s2_mmu_to_kvm(pgt->mmu);
+	kvm_pte_t pte;
+	long ret;
+
+	guard(read_lock)(&kvm->mmu_lock);
+
+	ret = kvm_pgtable_get_leaf(pgt, gpa, &pte, level,
+				   KVM_PGTABLE_WALK_SHARED);
+	if (ret)
+		return ret;
+	/* Unpopulated, must fault. */
+	if (!kvm_pte_valid(pte))
+		return 0;
+	/* Walked the entry so mark young. */
+	if (!kvm_pte_young_s2(pte))
+		kvm_pte_mkyoung_s2(pgt, gpa);
+	return kvm_granule_size(*level);
+}
+
+/* Synthesised data abort at specified page table level. */
+#define PRE_FAULT_ESR(level)				\
+	 ((ESR_ELx_EC_DABT_LOW << ESR_ELx_EC_SHIFT) |	\
+	  ESR_ELx_IL | ESR_ELx_FSC_FAULT_L(level))
+
+/* Retrieve either a read-only or a read/write hva. */
+static hva_t gfn_to_hva_memslot_read(struct kvm_memory_slot *slot, gfn_t gfn)
+{
+	return gfn_to_hva_memslot_prot(slot, gfn, /*writable=*/NULL);
+}
+
+static long __pre_fault_s2(struct kvm_s2_mmu *mmu, struct kvm_vcpu *vcpu,
+			   gpa_t gpa, struct kvm_memory_slot *memslot, s8 level)
+{
+	const bool is_gmem  = kvm_slot_has_gmem(memslot);
+	const gfn_t gfn = gpa_to_gfn(gpa);
+	const hva_t hva = is_gmem ? 0 : gfn_to_hva_memslot_read(memslot, gfn);
+	const struct kvm_s2_fault_desc s2fd = {
+		.vcpu		= vcpu,
+		.fault_ipa	= gpa,
+		.nested		= NULL,
+		.memslot	= memslot,
+		.hva		= hva,
+		.esr		= PRE_FAULT_ESR(level),
+		.mmu		= mmu,
+		.pre_fault	= true,
+	};
+	struct kvm_s2_fault_result result = {};
+	long ret;
+
+	if (kvm_is_error_hva(hva))
+		return -EFAULT;
+
+	if (is_gmem)
+		ret = gmem_abort(&s2fd, &result);
+	else
+		ret = user_mem_abort(&s2fd, &result);
+	if (IS_ERR_VALUE(ret))
+		return ret;
+	if (!result.mapped)
+		return -EAGAIN;
+	return result.mapping_size;
+}
+
+static long pre_fault_s2(struct kvm_s2_mmu *mmu, struct kvm_vcpu *vcpu,
+			 gpa_t gpa, struct kvm_memory_slot *memslot)
+{
+	s8 level = KVM_PGTABLE_LAST_LEVEL;
+	long ret;
+
+	/* Try a walk first. */
+	ret = kvm_walk_s2(mmu->pgt, gpa, &level);
+	if (ret)
+		return ret;
+	/* OK, have to fault page in. */
+	return __pre_fault_s2(mmu, vcpu, gpa, memslot, level);
+}
+
+static unsigned long
+pre_fault_bytes_consumed(gpa_t gpa, unsigned long granule_size,
+			 unsigned long bytes_remaining)
+{
+	/* Granules are always a power-of-2. */
+	const unsigned long granule_bytes_remaining =
+		granule_size - (gpa % granule_size);
+
+	return min(granule_bytes_remaining, bytes_remaining);
+}
+
+/* If you lose the race this many times, time to give up. */
+#define MAX_PRE_FAULT_RETRIES 3
+
+/**
+ * kvm_arch_vcpu_pre_fault_memory - pre-fault stage-2 page tables for the
+ * specified GPA.
+ * @vcpu:	The VCPU pointer
+ * @range:	{gpa, size, flags} tuple
+ *
+ * The mapping performed is always best-effort - faulting in is necessarily
+ * racey. The ranges faulted in are canonical, nested page tables are ignored.
+ *
+ * If the GPA is already mapped, the page table entry is marked young.
+ *
+ * @range->gpa specifies the GPA to pre-fault, @range->size specifies how many
+ * bytes remain to be pre-faulted and @range->flags is reserved and must be 0.
+ *
+ * Returns: the number of bytes the pre-fault consumed, or an error.
+ */
+long kvm_arch_vcpu_pre_fault_memory(struct kvm_vcpu *vcpu,
+				    struct kvm_pre_fault_memory *range)
+{
+	struct kvm *kvm = vcpu->kvm;
+	const u64 bytes_remaining = range->size;
+	struct kvm_s2_mmu *mmu = &kvm->arch.mmu; /* Canonical. */
+	struct kvm_memory_slot *memslot;
+	const gpa_t gpa = range->gpa;
+	int num_retries = 0;
+	long ret;
+
+	/*
+	 * pKVM is unsupported as their vCPUs are instantiated on first run and
+	 * pre-faulting only running vCPUs would be inconsistent and confusing.
+	 */
+	if (is_protected_kvm_enabled())
+		return -EOPNOTSUPP;
+
+	memslot = gfn_to_memslot(kvm, gpa_to_gfn(gpa));
+	if (!memslot)
+		return -ENOENT;
+	/* SRCU must be released for progress and only userland can do that. */
+	if (memslot->flags & KVM_MEMSLOT_INVALID)
+		return -EAGAIN;
+
+	do {
+		ret = pre_fault_s2(mmu, vcpu, gpa, memslot);
+	} while (ret == -EAGAIN && num_retries++ < MAX_PRE_FAULT_RETRIES);
+
+	if (IS_ERR_VALUE(ret))
+		return ret;
+	return pre_fault_bytes_consumed(gpa, ret, bytes_remaining);
+}

-- 
2.55.0

[PATCH 6/8] KVM: selftests: Enable pre_fault_memory_test for arm64

[Lorenzo Stoakes (ARM)]

From: Jack Thomson <jackabt@amazon.com>

Enable the pre_fault_memory_test to run on arm64 by making it work with
different guest page sizes and testing multiple guest configurations.

Update the test_assert to compare against the UCALL_EXIT_REASON, for
portability, as arm64 exits with KVM_EXIT_MMIO while x86 uses
KVM_EXIT_IO.

Signed-off-by: Jack Thomson <jackabt@amazon.com>
[ljs: merge conflict resolution with commit c847704619da]
Signed-off-by: Lorenzo Stoakes (ARM) <ljs@kernel.org>
---
 tools/testing/selftests/kvm/Makefile.kvm           |   1 +
 .../testing/selftests/kvm/pre_fault_memory_test.c  | 117 +++++++++++++++++----
 2 files changed, 96 insertions(+), 22 deletions(-)

diff --git a/tools/testing/selftests/kvm/Makefile.kvm b/tools/testing/selftests/kvm/Makefile.kvm
index 5f8d17ee5f67..66a9a4e62888 100644
--- a/tools/testing/selftests/kvm/Makefile.kvm
+++ b/tools/testing/selftests/kvm/Makefile.kvm
@@ -199,6 +199,7 @@ TEST_GEN_PROGS_arm64 += guest_memfd_test
 TEST_GEN_PROGS_arm64 += mmu_stress_test
 TEST_GEN_PROGS_arm64 += rseq_test
 TEST_GEN_PROGS_arm64 += steal_time
+TEST_GEN_PROGS_arm64 += pre_fault_memory_test
 
 TEST_GEN_PROGS_s390 = $(TEST_GEN_PROGS_COMMON)
 TEST_GEN_PROGS_s390 += s390/memop
diff --git a/tools/testing/selftests/kvm/pre_fault_memory_test.c b/tools/testing/selftests/kvm/pre_fault_memory_test.c
index a0fcae3cb7a8..ee77c51cc566 100644
--- a/tools/testing/selftests/kvm/pre_fault_memory_test.c
+++ b/tools/testing/selftests/kvm/pre_fault_memory_test.c
@@ -12,19 +12,29 @@
 #include <processor.h>
 #include <pthread.h>
 #include <ucall_common.h>
+#include <guest_modes.h>
 
 /* Arbitrarily chosen values */
-#define TEST_SIZE		(SZ_2M + PAGE_SIZE)
-#define TEST_NPAGES		(TEST_SIZE / PAGE_SIZE)
+#define TEST_BASE_SIZE		SZ_2M
 #define TEST_SLOT		10
 
+/* Storage of test info to share with guest code */
+struct test_config {
+	u64 page_size;
+	u64 test_size;
+	u64 test_num_pages;
+};
+
+static struct test_config test_config;
+
 static void guest_code(u64 base_gva)
 {
 	volatile u64 val __used;
+	struct test_config *config = &test_config;
 	int i;
 
-	for (i = 0; i < TEST_NPAGES; i++) {
-		u64 *src = (u64 *)(base_gva + i * PAGE_SIZE);
+	for (i = 0; i < config->test_num_pages; i++) {
+		u64 *src = (u64 *)(base_gva + i * config->page_size);
 
 		val = *src;
 	}
@@ -57,7 +67,7 @@ static void *delete_slot_worker(void *__data)
 		cpu_relax();
 
 	vm_userspace_mem_region_add(vm, VM_MEM_SRC_ANONYMOUS, data->gpa,
-				    TEST_SLOT, TEST_NPAGES, data->flags);
+				    TEST_SLOT, test_config.test_num_pages, data->flags);
 
 	return NULL;
 }
@@ -150,8 +160,8 @@ static void pre_fault_memory(struct kvm_vcpu *vcpu, u64 base_gpa, u64 offset,
 	/*
 	 * Assert success if prefaulting the entire range should succeed, i.e.
 	 * complete with no bytes remaining.  Otherwise prefaulting should have
-	 * failed due to ENOENT (due to RET_PF_EMULATE for emulated MMIO when
-	 * no memslot exists).
+	 * failed due to ENOENT (no memslot exists for the GPA; on x86 this
+	 * surfaces via RET_PF_EMULATE).
 	 */
 	if (!expected_left)
 		TEST_ASSERT_VM_VCPU_IOCTL(!ret, KVM_PRE_FAULT_MEMORY, ret, vcpu->vm);
@@ -160,39 +170,72 @@ static void pre_fault_memory(struct kvm_vcpu *vcpu, u64 base_gpa, u64 offset,
 					  KVM_PRE_FAULT_MEMORY, ret, vcpu->vm);
 }
 
-static void __test_pre_fault_memory(unsigned long vm_type, bool private)
+struct test_params {
+	unsigned long vm_type;
+	bool private;
+};
+
+static void __test_pre_fault_memory(enum vm_guest_mode guest_mode, void *arg)
 {
-	gpa_t gpa, gva, alignment, guest_page_size;
+	gpa_t gpa, gva, alignment, guest_page_size, host_page_size;
+	struct test_params *p = arg;
 	const struct vm_shape shape = {
-		.mode = VM_MODE_DEFAULT,
-		.type = vm_type,
+		.mode = guest_mode,
+		.type = p->vm_type,
 	};
 	struct kvm_vcpu *vcpu;
+	struct kvm_run *run;
 	struct kvm_vm *vm;
 	struct ucall uc;
 
+	pr_info("Testing guest mode: %s\n", vm_guest_mode_string(guest_mode));
+
 	vm = vm_create_shape_with_one_vcpu(shape, &vcpu, guest_code);
 
-	alignment = guest_page_size = vm_guest_mode_params[VM_MODE_DEFAULT].page_size;
-	gpa = (vm->max_gfn - TEST_NPAGES) * guest_page_size;
+	guest_page_size = vm_guest_mode_params[guest_mode].page_size;
+	host_page_size = getpagesize();
+
+	test_config.page_size = guest_page_size;
+	test_config.test_size = align_up(TEST_BASE_SIZE + test_config.page_size,
+					 host_page_size);
+	test_config.test_num_pages = vm_calc_num_guest_pages(vm->mode, test_config.test_size);
+
+	gpa = (vm->max_gfn - test_config.test_num_pages) * test_config.page_size;
 	alignment = SZ_2M;
+	alignment = max(alignment, host_page_size);
 	gpa = align_down(gpa, alignment);
 	gva = gpa & ((1ULL << (vm->va_bits - 1)) - 1);
 
-	vm_userspace_mem_region_add(vm, VM_MEM_SRC_ANONYMOUS, gpa, TEST_SLOT,
-				    TEST_NPAGES, private ? KVM_MEM_GUEST_MEMFD : 0);
-	virt_map(vm, gva, gpa, TEST_NPAGES);
+	vm_userspace_mem_region_add(vm, VM_MEM_SRC_ANONYMOUS,
+				    gpa, TEST_SLOT, test_config.test_num_pages,
+				    p->private ? KVM_MEM_GUEST_MEMFD : 0);
+	virt_map(vm, gva, gpa, test_config.test_num_pages);
 
-	if (private)
-		vm_mem_set_private(vm, gpa, TEST_SIZE);
+	if (p->private)
+		vm_mem_set_private(vm, gpa, test_config.test_size);
 
-	pre_fault_memory(vcpu, gpa, 0, SZ_2M, 0, private);
-	pre_fault_memory(vcpu, gpa, SZ_2M, PAGE_SIZE * 2, PAGE_SIZE, private);
-	pre_fault_memory(vcpu, gpa, TEST_SIZE, PAGE_SIZE, PAGE_SIZE, private);
+	pre_fault_memory(vcpu, gpa, 0, test_config.test_size, 0, p->private);
+	/* Retry the same range after the first prefault attempt. */
+	pre_fault_memory(vcpu, gpa, 0, test_config.test_size, 0, p->private);
+	pre_fault_memory(vcpu, gpa,
+			 test_config.test_size - host_page_size,
+			 host_page_size * 2, host_page_size, p->private);
+	pre_fault_memory(vcpu, gpa, test_config.test_size,
+			 host_page_size, host_page_size, p->private);
 
 	vcpu_args_set(vcpu, 1, gva);
+
+	/* Export the shared variables to the guest. */
+	sync_global_to_guest(vm, test_config);
+
 	vcpu_run(vcpu);
 
+	run = vcpu->run;
+	TEST_ASSERT(run->exit_reason == UCALL_EXIT_REASON,
+		    "Wanted %s, got exit reason: %u (%s)",
+		    exit_reason_str(UCALL_EXIT_REASON),
+		    run->exit_reason, exit_reason_str(run->exit_reason));
+
 	switch (get_ucall(vcpu, &uc)) {
 	case UCALL_ABORT:
 		REPORT_GUEST_ASSERT(uc);
@@ -209,16 +252,46 @@ static void __test_pre_fault_memory(unsigned long vm_type, bool private)
 
 static void test_pre_fault_memory(unsigned long vm_type, bool private)
 {
+	struct test_params p = {
+		.vm_type = vm_type,
+		.private = private,
+	};
+
 	if (vm_type && !(kvm_check_cap(KVM_CAP_VM_TYPES) & BIT(vm_type))) {
 		pr_info("Skipping tests for vm_type 0x%lx\n", vm_type);
 		return;
 	}
 
-	__test_pre_fault_memory(vm_type, private);
+	for_each_guest_mode(__test_pre_fault_memory, &p);
+}
+
+static void help(char *name)
+{
+	puts("");
+	printf("usage: %s [-h] [-m mode]\n", name);
+	puts("");
+	guest_modes_help();
+	puts("");
 }
 
 int main(int argc, char *argv[])
 {
+	int opt;
+
+	guest_modes_append_default();
+
+	while ((opt = getopt(argc, argv, "hm:")) != -1) {
+		switch (opt) {
+		case 'm':
+			guest_modes_cmdline(optarg);
+			break;
+		case 'h':
+		default:
+			help(argv[0]);
+			exit(0);
+		}
+	}
+
 	TEST_REQUIRE(kvm_check_cap(KVM_CAP_PRE_FAULT_MEMORY));
 
 	test_pre_fault_memory(0, false);

-- 
2.55.0

[PATCH 7/8] KVM: selftests: Add option for different backing in pre-fault tests

[Lorenzo Stoakes (ARM)]

From: Jack Thomson <jackabt@amazon.com>

Add a -s option to specify different memory backing types for the
pre-fault tests (e.g. anonymous, hugetlb), allowing testing of the
pre-fault functionality across different memory configurations.

Signed-off-by: Jack Thomson <jackabt@amazon.com>
Signed-off-by: Lorenzo Stoakes (ARM) <ljs@kernel.org>
---
 .../testing/selftests/kvm/pre_fault_memory_test.c  | 51 +++++++++++++++-------
 1 file changed, 36 insertions(+), 15 deletions(-)

diff --git a/tools/testing/selftests/kvm/pre_fault_memory_test.c b/tools/testing/selftests/kvm/pre_fault_memory_test.c
index ee77c51cc566..702c72bbfa96 100644
--- a/tools/testing/selftests/kvm/pre_fault_memory_test.c
+++ b/tools/testing/selftests/kvm/pre_fault_memory_test.c
@@ -46,6 +46,7 @@ struct slot_worker_data {
 	struct kvm_vm *vm;
 	gpa_t gpa;
 	u32 flags;
+	enum vm_mem_backing_src_type mem_backing_src;
 	bool worker_ready;
 	bool prefault_ready;
 	bool recreate_slot;
@@ -66,14 +67,16 @@ static void *delete_slot_worker(void *__data)
 	while (!READ_ONCE(data->recreate_slot))
 		cpu_relax();
 
-	vm_userspace_mem_region_add(vm, VM_MEM_SRC_ANONYMOUS, data->gpa,
+	vm_userspace_mem_region_add(vm, data->mem_backing_src, data->gpa,
 				    TEST_SLOT, test_config.test_num_pages, data->flags);
 
 	return NULL;
 }
 
 static void pre_fault_memory(struct kvm_vcpu *vcpu, u64 base_gpa, u64 offset,
-			     u64 size, u64 expected_left, bool private)
+			     u64 size, u64 expected_left,
+			     enum vm_mem_backing_src_type mem_backing_src,
+			     bool private)
 {
 	struct kvm_pre_fault_memory range = {
 		.gpa = base_gpa + offset,
@@ -84,6 +87,7 @@ static void pre_fault_memory(struct kvm_vcpu *vcpu, u64 base_gpa, u64 offset,
 		.vm = vcpu->vm,
 		.gpa = base_gpa,
 		.flags = private ? KVM_MEM_GUEST_MEMFD : 0,
+		.mem_backing_src = mem_backing_src,
 	};
 	bool slot_recreated = false;
 	pthread_t slot_worker;
@@ -173,11 +177,13 @@ static void pre_fault_memory(struct kvm_vcpu *vcpu, u64 base_gpa, u64 offset,
 struct test_params {
 	unsigned long vm_type;
 	bool private;
+	enum vm_mem_backing_src_type mem_backing_src;
 };
 
 static void __test_pre_fault_memory(enum vm_guest_mode guest_mode, void *arg)
 {
 	gpa_t gpa, gva, alignment, guest_page_size, host_page_size;
+	gpa_t backing_src_pagesz, mem_page_size;
 	struct test_params *p = arg;
 	const struct vm_shape shape = {
 		.mode = guest_mode,
@@ -189,24 +195,28 @@ static void __test_pre_fault_memory(enum vm_guest_mode guest_mode, void *arg)
 	struct ucall uc;
 
 	pr_info("Testing guest mode: %s\n", vm_guest_mode_string(guest_mode));
+	pr_info("Testing memory backing src type: %s\n",
+		vm_mem_backing_src_alias(p->mem_backing_src)->name);
 
 	vm = vm_create_shape_with_one_vcpu(shape, &vcpu, guest_code);
 
 	guest_page_size = vm_guest_mode_params[guest_mode].page_size;
 	host_page_size = getpagesize();
+	backing_src_pagesz = get_backing_src_pagesz(p->mem_backing_src);
+	mem_page_size = max(host_page_size, backing_src_pagesz);
 
 	test_config.page_size = guest_page_size;
 	test_config.test_size = align_up(TEST_BASE_SIZE + test_config.page_size,
-					 host_page_size);
+					 mem_page_size);
 	test_config.test_num_pages = vm_calc_num_guest_pages(vm->mode, test_config.test_size);
 
 	gpa = (vm->max_gfn - test_config.test_num_pages) * test_config.page_size;
 	alignment = SZ_2M;
-	alignment = max(alignment, host_page_size);
+	alignment = max(alignment, mem_page_size);
 	gpa = align_down(gpa, alignment);
 	gva = gpa & ((1ULL << (vm->va_bits - 1)) - 1);
 
-	vm_userspace_mem_region_add(vm, VM_MEM_SRC_ANONYMOUS,
+	vm_userspace_mem_region_add(vm, p->mem_backing_src,
 				    gpa, TEST_SLOT, test_config.test_num_pages,
 				    p->private ? KVM_MEM_GUEST_MEMFD : 0);
 	virt_map(vm, gva, gpa, test_config.test_num_pages);
@@ -214,14 +224,18 @@ static void __test_pre_fault_memory(enum vm_guest_mode guest_mode, void *arg)
 	if (p->private)
 		vm_mem_set_private(vm, gpa, test_config.test_size);
 
-	pre_fault_memory(vcpu, gpa, 0, test_config.test_size, 0, p->private);
+	pre_fault_memory(vcpu, gpa, 0, test_config.test_size, 0,
+			 p->mem_backing_src, p->private);
 	/* Retry the same range after the first prefault attempt. */
-	pre_fault_memory(vcpu, gpa, 0, test_config.test_size, 0, p->private);
+	pre_fault_memory(vcpu, gpa, 0, test_config.test_size, 0,
+			 p->mem_backing_src, p->private);
 	pre_fault_memory(vcpu, gpa,
 			 test_config.test_size - host_page_size,
-			 host_page_size * 2, host_page_size, p->private);
+			 host_page_size * 2, host_page_size,
+			 p->mem_backing_src, p->private);
 	pre_fault_memory(vcpu, gpa, test_config.test_size,
-			 host_page_size, host_page_size, p->private);
+			 host_page_size, host_page_size,
+			 p->mem_backing_src, p->private);
 
 	vcpu_args_set(vcpu, 1, gva);
 
@@ -250,11 +264,13 @@ static void __test_pre_fault_memory(enum vm_guest_mode guest_mode, void *arg)
 	kvm_vm_free(vm);
 }
 
-static void test_pre_fault_memory(unsigned long vm_type, bool private)
+static void test_pre_fault_memory(unsigned long vm_type, enum vm_mem_backing_src_type backing_src,
+				  bool private)
 {
 	struct test_params p = {
 		.vm_type = vm_type,
 		.private = private,
+		.mem_backing_src = backing_src,
 	};
 
 	if (vm_type && !(kvm_check_cap(KVM_CAP_VM_TYPES) & BIT(vm_type))) {
@@ -268,23 +284,28 @@ static void test_pre_fault_memory(unsigned long vm_type, bool private)
 static void help(char *name)
 {
 	puts("");
-	printf("usage: %s [-h] [-m mode]\n", name);
+	printf("usage: %s [-h] [-m mode] [-s mem-type]\n", name);
 	puts("");
 	guest_modes_help();
+	backing_src_help("-s");
 	puts("");
 }
 
 int main(int argc, char *argv[])
 {
+	enum vm_mem_backing_src_type backing = DEFAULT_VM_MEM_SRC;
 	int opt;
 
 	guest_modes_append_default();
 
-	while ((opt = getopt(argc, argv, "hm:")) != -1) {
+	while ((opt = getopt(argc, argv, "hm:s:")) != -1) {
 		switch (opt) {
 		case 'm':
 			guest_modes_cmdline(optarg);
 			break;
+		case 's':
+			backing = parse_backing_src_type(optarg);
+			break;
 		case 'h':
 		default:
 			help(argv[0]);
@@ -294,10 +315,10 @@ int main(int argc, char *argv[])
 
 	TEST_REQUIRE(kvm_check_cap(KVM_CAP_PRE_FAULT_MEMORY));
 
-	test_pre_fault_memory(0, false);
+	test_pre_fault_memory(0, backing, false);
 #ifdef __x86_64__
-	test_pre_fault_memory(KVM_X86_SW_PROTECTED_VM, false);
-	test_pre_fault_memory(KVM_X86_SW_PROTECTED_VM, true);
+	test_pre_fault_memory(KVM_X86_SW_PROTECTED_VM, backing, false);
+	test_pre_fault_memory(KVM_X86_SW_PROTECTED_VM, backing, true);
 #endif
 	return 0;
 }

-- 
2.55.0

[PATCH 8/8] KVM: selftests: Add nested pre-fault test for arm64

[Lorenzo Stoakes (ARM)]

From: Jack Thomson <jackabt@amazon.com>

Add an arm64 nested-virt selftest for KVM_PRE_FAULT_MEMORY. The guest
enters vEL1 and exits to userspace with a nested/shadow stage-2 MMU as
the vCPU's last-run context.

Before prefaulting, userspace enables HCR_EL2.VM and points VTTBR_EL2 at
an empty nested stage-2 root. A prefault implementation that incorrectly
treats the userspace GPA as an L2 IPA will fail the ioctl; the correct
path targets the canonical stage-2 and succeeds.

Restore the original nested state before resuming the guest, then touch
the prefaulted range to check that vEL1 still runs correctly.

Signed-off-by: Jack Thomson <jackabt@amazon.com>
[ljs: partial progress, >4 KiB pgsize, commit msg, comment fixups]
Signed-off-by: Lorenzo Stoakes (ARM) <ljs@kernel.org>
---
 tools/testing/selftests/kvm/Makefile.kvm           |   1 +
 .../selftests/kvm/arm64/nv_pre_fault_memory_test.c | 206 +++++++++++++++++++++
 2 files changed, 207 insertions(+)

diff --git a/tools/testing/selftests/kvm/Makefile.kvm b/tools/testing/selftests/kvm/Makefile.kvm
index 66a9a4e62888..1e0edd0f99f7 100644
--- a/tools/testing/selftests/kvm/Makefile.kvm
+++ b/tools/testing/selftests/kvm/Makefile.kvm
@@ -173,6 +173,7 @@ TEST_GEN_PROGS_arm64 += arm64/debug-exceptions
 TEST_GEN_PROGS_arm64 += arm64/hello_el2
 TEST_GEN_PROGS_arm64 += arm64/host_sve
 TEST_GEN_PROGS_arm64 += arm64/hypercalls
+TEST_GEN_PROGS_arm64 += arm64/nv_pre_fault_memory_test
 TEST_GEN_PROGS_arm64 += arm64/external_aborts
 TEST_GEN_PROGS_arm64 += arm64/mmio_sign_ext
 TEST_GEN_PROGS_arm64 += arm64/page_fault_test
diff --git a/tools/testing/selftests/kvm/arm64/nv_pre_fault_memory_test.c b/tools/testing/selftests/kvm/arm64/nv_pre_fault_memory_test.c
new file mode 100644
index 000000000000..b3833aea2a34
--- /dev/null
+++ b/tools/testing/selftests/kvm/arm64/nv_pre_fault_memory_test.c
@@ -0,0 +1,206 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * nv_pre_fault_memory_test - Test KVM_PRE_FAULT_MEMORY on a vCPU whose
+ * last-run context is nested.
+ *
+ * The guest starts at vEL2, mirrors its EL2 translation regime into the
+ * real EL1 registers, drops HCR_EL2.TGE and ERETs to vEL1, then exits to
+ * userspace from vEL1 so that the vCPU's last-run context selects a
+ * shadow stage-2 MMU. Userspace then enables an empty nested stage-2
+ * before prefaulting. Prefaulting must target the canonical stage-2,
+ * regardless of the vCPU's nested state.
+ */
+#include "kvm_util.h"
+#include "processor.h"
+#include "test_util.h"
+#include "ucall.h"
+
+#include <asm/sysreg.h>
+#include <linux/sizes.h>
+
+#define TEST_MEM_SLOT		10
+#define NESTED_S2_ROOT_SLOT	11
+#define TEST_MEM_SIZE		SZ_2M
+#define TEST_MEM_GPA		SZ_1G
+#define NESTED_S2_ROOT_GPA	(TEST_MEM_GPA + TEST_MEM_SIZE)
+
+struct nested_s2_state {
+	u64 hcr_el2;
+	u64 vttbr_el2;
+};
+
+static void guest_el1_code(void)
+{
+	u64 offset;
+
+	GUEST_ASSERT_EQ(get_current_el(), 1);
+
+	/* Exit to userspace with the vEL1 (nested) context live. */
+	GUEST_SYNC(1);
+
+	/*
+	 * Touch the prefaulted range. vstage-2 is disabled, so the shadow
+	 * stage-2 is a 1:1 view of the canonical IPA space.
+	 */
+	for (offset = 0; offset < TEST_MEM_SIZE; offset += SZ_4K)
+		READ_ONCE(*(u64 *)(TEST_MEM_GPA + offset));
+
+	GUEST_DONE();
+}
+
+static void guest_code(void)
+{
+	u64 sp;
+
+	GUEST_ASSERT_EQ(get_current_el(), 2);
+
+	/*
+	 * Mirror the EL2 translation regime into the real EL1 registers so
+	 * that vEL1 runs on the test's stage-1 page tables. With E2H=1, the
+	 * _EL1 accessors read the EL2 registers, and the _EL12 accessors
+	 * write the real EL1 registers.
+	 */
+	write_sysreg_s(read_sysreg(sctlr_el1), SYS_SCTLR_EL12);
+	write_sysreg_s(read_sysreg(tcr_el1), SYS_TCR_EL12);
+	write_sysreg_s(read_sysreg(ttbr0_el1), SYS_TTBR0_EL12);
+	write_sysreg_s(read_sysreg(mair_el1), SYS_MAIR_EL12);
+	write_sysreg_s(read_sysreg(cpacr_el1), SYS_CPACR_EL12);
+
+	/* Run vEL1 on the same stack. */
+	asm volatile("mov %0, sp" : "=r"(sp));
+	write_sysreg(sp, sp_el1);
+
+	/*
+	 * Drop TGE so that vEL1 is a nested context rather than host EL0.
+	 * KVM backs it with a shadow stage-2 MMU even though vstage-2 is
+	 * disabled (HCR_EL2.VM=0).
+	 */
+	write_sysreg(read_sysreg(hcr_el2) & ~HCR_EL2_TGE, hcr_el2);
+	isb();
+
+	write_sysreg(PSR_MODE_EL1h | PSR_F_BIT | PSR_I_BIT | PSR_A_BIT |
+		     PSR_D_BIT, spsr_el2);
+	write_sysreg((u64)guest_el1_code, elr_el2);
+	asm volatile("eret");
+
+	GUEST_ASSERT(false);
+}
+
+static void pre_fault(struct kvm_vcpu *vcpu, u64 gpa, u64 size)
+{
+	struct kvm_pre_fault_memory range = {
+		.gpa = gpa,
+		.size = size,
+	};
+	int ret;
+
+	do {
+		ret = __vcpu_ioctl(vcpu, KVM_PRE_FAULT_MEMORY, &range);
+	} while ((!ret && range.size) ||
+		 (ret < 0 && (errno == EINTR || errno == EAGAIN)));
+
+	TEST_ASSERT(!ret, "KVM_PRE_FAULT_MEMORY failed, ret: %d errno: %d",
+		    ret, errno);
+	TEST_ASSERT_EQ(range.size, 0);
+}
+
+static struct nested_s2_state enable_empty_nested_s2(struct kvm_vcpu *vcpu)
+{
+	struct nested_s2_state state = {
+		.hcr_el2 = vcpu_get_reg(vcpu, KVM_ARM64_SYS_REG(SYS_HCR_EL2)),
+		.vttbr_el2 = vcpu_get_reg(vcpu,
+					   KVM_ARM64_SYS_REG(SYS_VTTBR_EL2)),
+	};
+
+	TEST_ASSERT(!(state.hcr_el2 & HCR_EL2_TGE),
+		    "vCPU should be in nested/vEL1 context");
+
+	vcpu_set_reg(vcpu, KVM_ARM64_SYS_REG(SYS_VTTBR_EL2),
+		     NESTED_S2_ROOT_GPA);
+	vcpu_set_reg(vcpu, KVM_ARM64_SYS_REG(SYS_HCR_EL2),
+		     state.hcr_el2 | HCR_EL2_VM);
+
+	return state;
+}
+
+static void restore_nested_s2(struct kvm_vcpu *vcpu,
+			      struct nested_s2_state *state)
+{
+	vcpu_set_reg(vcpu, KVM_ARM64_SYS_REG(SYS_HCR_EL2), state->hcr_el2);
+	vcpu_set_reg(vcpu, KVM_ARM64_SYS_REG(SYS_VTTBR_EL2),
+		     state->vttbr_el2);
+}
+
+int main(void)
+{
+	struct nested_s2_state s2;
+	struct kvm_vcpu_init init;
+	struct kvm_vcpu *vcpu;
+	struct kvm_vm *vm;
+	struct ucall uc;
+	u64 npages;
+
+	TEST_REQUIRE(kvm_check_cap(KVM_CAP_ARM_EL2));
+	TEST_REQUIRE(kvm_check_cap(KVM_CAP_PRE_FAULT_MEMORY));
+
+	vm = vm_create(1);
+
+	kvm_get_default_vcpu_target(vm, &init);
+	init.features[0] |= BIT(KVM_ARM_VCPU_HAS_EL2);
+	vcpu = aarch64_vcpu_add(vm, 0, &init, guest_code);
+	kvm_arch_vm_finalize_vcpus(vm);
+
+	npages = TEST_MEM_SIZE / vm->page_size;
+	vm_userspace_mem_region_add(vm, VM_MEM_SRC_ANONYMOUS, TEST_MEM_GPA,
+				    TEST_MEM_SLOT, npages, 0);
+	virt_map(vm, TEST_MEM_GPA, TEST_MEM_GPA, npages);
+
+	vm_userspace_mem_region_add(vm, VM_MEM_SRC_ANONYMOUS,
+				    NESTED_S2_ROOT_GPA, NESTED_S2_ROOT_SLOT,
+				    vm_adjust_num_guest_pages(vm->mode, 1), 0);
+
+	/* Run the guest until it has ERET'd from vEL2 to vEL1. */
+	vcpu_run(vcpu);
+	switch (get_ucall(vcpu, &uc)) {
+	case UCALL_SYNC:
+		TEST_ASSERT_EQ(uc.args[1], 1);
+		break;
+	case UCALL_ABORT:
+		REPORT_GUEST_ASSERT(uc);
+		break;
+	default:
+		TEST_FAIL("Unhandled ucall: %ld", uc.cmd);
+	}
+
+	/*
+	 * The vCPU's last-run context is vEL1, backed by a shadow stage-2
+	 * MMU. Enable nested stage-2 with an empty root so that the ioctl
+	 * fails if it tries to interpret the userspace GPA as an L2 IPA.
+	 *
+	 * Prefault in two halves so that the second ioctl exercises a
+	 * repeated shadow-MMU attach and canonical stage-2 swap.
+	 *
+	 * (Note that an implementation that wrongly populates shadow
+	 * stage-2 page tables would not be caught as userland can't
+	 * inspect these.)
+	 */
+	s2 = enable_empty_nested_s2(vcpu);
+	pre_fault(vcpu, TEST_MEM_GPA, TEST_MEM_SIZE / 2);
+	pre_fault(vcpu, TEST_MEM_GPA + TEST_MEM_SIZE / 2, TEST_MEM_SIZE / 2);
+	restore_nested_s2(vcpu, &s2);
+
+	/* Resume at vEL1 and touch the prefaulted range. */
+	vcpu_run(vcpu);
+	switch (get_ucall(vcpu, &uc)) {
+	case UCALL_DONE:
+		break;
+	case UCALL_ABORT:
+		REPORT_GUEST_ASSERT(uc);
+		break;
+	default:
+		TEST_FAIL("Unhandled ucall: %ld", uc.cmd);
+	}
+
+	kvm_vm_free(vm);
+	return 0;
+}

-- 
2.55.0