[PATCH v3 0/9] KVM: arm64: Add support for FEAT_IDST

[PATCH v3 0/9] KVM: arm64: Add support for FEAT_IDST

[Marc Zyngier]

FEAT_IDST appeared in ARMv8.4, and allows ID registers to be trapped
if they are not implemented. This only concerns 3 registers (GMID_EL1,
CCSIDR2_EL1 and SMIDR_EL1), which are part of features that may not be
exposed to the guest even if present on the host.

For these registers, the HW should report them with EC=0x18, even if
the feature isn't implemented.

Add support for this feature by handling these registers in a specific
way and implementing GMID_EL1 support in the process. A very basic
selftest checks that these registers behave as expected.

* From v2: [2]

  - Repainted ID_AA64MMFR2_EL1.IDS description (Oliver)

  - Made the IDST handling more generic in the core KVM code, which
    resulted in the series being restructured a bit

  - Added handling to pKVM (in a slightly different way, as pKVM
    insist on seeing a full enumeration of the trapped registers)

  - Some cleanups

  - Collected RBs, with thanks

* From v1: [1]

  - Fixed commit message in patch #4 (Ben)

  - Collected RB, with thanks (Joey)

[1] https://lore.kernel.org/r/20251120133202.2037803-1-maz@kernel.org
[2] https://lore.kernel.org/r/20251126155951.1146317-1-maz@kernel.org

Marc Zyngier (9):
  arm64: Repaint ID_AA64MMFR2_EL1.IDS description
  KVM: arm64: Add trap routing for GMID_EL1
  KVM: arm64: Add a generic synchronous exception injection primitive
  KVM: arm64: Handle FEAT_IDST for sysregs without specific handlers
  KVM: arm64: Handle CSSIDR2_EL1 and SMIDR_EL1 in a generic way
  KVM: arm64: Force trap of GMID_EL1 when the guest doesn't have MTE
  KVM: arm64: pkvm: Add a generic synchronous exception injection
    primitive
  KVM: arm64: pkvm: Report optional ID register traps with a 0x18
    syndrome
  KVM: arm64: selftests: Add a test for FEAT_IDST

 arch/arm64/include/asm/kvm_emulate.h          |   1 +
 arch/arm64/kvm/emulate-nested.c               |  28 +++++
 arch/arm64/kvm/hyp/nvhe/sys_regs.c            |  39 ++++--
 arch/arm64/kvm/inject_fault.c                 |  10 +-
 arch/arm64/kvm/sys_regs.c                     |   4 +-
 arch/arm64/tools/sysreg                       |   4 +-
 tools/testing/selftests/kvm/Makefile.kvm      |   1 +
 .../testing/selftests/kvm/arm64/idreg-idst.c  | 117 ++++++++++++++++++
 8 files changed, 189 insertions(+), 15 deletions(-)
 create mode 100644 tools/testing/selftests/kvm/arm64/idreg-idst.c

-- 
2.47.3

[PATCH v3 1/9] arm64: Repaint ID_AA64MMFR2_EL1.IDS description

[Marc Zyngier]

ID_AA64MMFR2_EL1.IDS, as described in the sysreg file, is pretty horrible
as it diesctly give the ESR value. Repaint it using the usual NI/IMP
identifiers to describe the absence/presence of FEAT_IDST.

Signed-off-by: Marc Zyngier <maz@kernel.org>
---
 arch/arm64/kvm/hyp/nvhe/sys_regs.c | 2 +-
 arch/arm64/tools/sysreg            | 4 ++--
 2 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/arch/arm64/kvm/hyp/nvhe/sys_regs.c b/arch/arm64/kvm/hyp/nvhe/sys_regs.c
index 82da9b03692d4..107d62921b168 100644
--- a/arch/arm64/kvm/hyp/nvhe/sys_regs.c
+++ b/arch/arm64/kvm/hyp/nvhe/sys_regs.c
@@ -134,7 +134,7 @@ static const struct pvm_ftr_bits pvmid_aa64mmfr2[] = {
 	MAX_FEAT(ID_AA64MMFR2_EL1, UAO, IMP),
 	MAX_FEAT(ID_AA64MMFR2_EL1, IESB, IMP),
 	MAX_FEAT(ID_AA64MMFR2_EL1, AT, IMP),
-	MAX_FEAT_ENUM(ID_AA64MMFR2_EL1, IDS, 0x18),
+	MAX_FEAT_ENUM(ID_AA64MMFR2_EL1, IDS, IMP),
 	MAX_FEAT(ID_AA64MMFR2_EL1, TTL, IMP),
 	MAX_FEAT(ID_AA64MMFR2_EL1, BBM, 2),
 	MAX_FEAT(ID_AA64MMFR2_EL1, E0PD, IMP),
diff --git a/arch/arm64/tools/sysreg b/arch/arm64/tools/sysreg
index 1c6cdf9d54bba..3261e8791ac03 100644
--- a/arch/arm64/tools/sysreg
+++ b/arch/arm64/tools/sysreg
@@ -2257,8 +2257,8 @@ UnsignedEnum	43:40	FWB
 	0b0001	IMP
 EndEnum
 Enum	39:36	IDS
-	0b0000	0x0
-	0b0001	0x18
+	0b0000	NI
+	0b0001	IMP
 EndEnum
 UnsignedEnum	35:32	AT
 	0b0000	NI
-- 
2.47.3

[PATCH v3 2/9] KVM: arm64: Add trap routing for GMID_EL1

[Marc Zyngier]

HCR_EL2.TID5 is currently ignored by the trap routing infrastructure.
Wire it in the routing table so that GMID_EL1, the sole register
trapped by this bit, is correctly handled in the NV case.

Signed-off-by: Marc Zyngier <maz@kernel.org>
---
 arch/arm64/kvm/emulate-nested.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/arch/arm64/kvm/emulate-nested.c b/arch/arm64/kvm/emulate-nested.c
index 834f13fb1fb7d..616eb6ad68701 100644
--- a/arch/arm64/kvm/emulate-nested.c
+++ b/arch/arm64/kvm/emulate-nested.c
@@ -70,6 +70,7 @@ enum cgt_group_id {
 	CGT_HCR_ENSCXT,
 	CGT_HCR_TTLBIS,
 	CGT_HCR_TTLBOS,
+	CGT_HCR_TID5,
 
 	CGT_MDCR_TPMCR,
 	CGT_MDCR_TPM,
@@ -308,6 +309,12 @@ static const struct trap_bits coarse_trap_bits[] = {
 		.mask		= HCR_TTLBOS,
 		.behaviour	= BEHAVE_FORWARD_RW,
 	},
+	[CGT_HCR_TID5] = {
+		.index		= HCR_EL2,
+		.value		= HCR_TID5,
+		.mask		= HCR_TID5,
+		.behaviour	= BEHAVE_FORWARD_RW,
+	},
 	[CGT_MDCR_TPMCR] = {
 		.index		= MDCR_EL2,
 		.value		= MDCR_EL2_TPMCR,
@@ -665,6 +672,7 @@ static const struct encoding_to_trap_config encoding_to_cgt[] __initconst = {
 	SR_TRAP(SYS_CCSIDR2_EL1,	CGT_HCR_TID2_TID4),
 	SR_TRAP(SYS_CLIDR_EL1,		CGT_HCR_TID2_TID4),
 	SR_TRAP(SYS_CSSELR_EL1,		CGT_HCR_TID2_TID4),
+	SR_TRAP(SYS_GMID_EL1,		CGT_HCR_TID5),
 	SR_RANGE_TRAP(SYS_ID_PFR0_EL1,
 		      sys_reg(3, 0, 0, 7, 7), CGT_HCR_TID3),
 	SR_TRAP(SYS_ICC_SGI0R_EL1,	CGT_HCR_IMO_FMO_ICH_HCR_TC),
-- 
2.47.3

[PATCH v3 3/9] KVM: arm64: Add a generic synchronous exception injection primitive

[Marc Zyngier]

Maybe in a surprising way, we don't currently have a generic way
to inject a synchronous exception at the EL the vcpu is currently
running at.

Extract such primitive from the UNDEF injection code.

Reviewed-by: Ben Horgan <ben.horgan@arm.com>
Reviewed-by: Yuan Yao <yaoyuan@linux.alibaba.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>
---
 arch/arm64/include/asm/kvm_emulate.h |  1 +
 arch/arm64/kvm/inject_fault.c        | 10 +++++++---
 2 files changed, 8 insertions(+), 3 deletions(-)

diff --git a/arch/arm64/include/asm/kvm_emulate.h b/arch/arm64/include/asm/kvm_emulate.h
index c9eab316398e2..df20d47f0d256 100644
--- a/arch/arm64/include/asm/kvm_emulate.h
+++ b/arch/arm64/include/asm/kvm_emulate.h
@@ -45,6 +45,7 @@ bool kvm_condition_valid32(const struct kvm_vcpu *vcpu);
 void kvm_skip_instr32(struct kvm_vcpu *vcpu);
 
 void kvm_inject_undefined(struct kvm_vcpu *vcpu);
+void kvm_inject_sync(struct kvm_vcpu *vcpu, u64 esr);
 int kvm_inject_serror_esr(struct kvm_vcpu *vcpu, u64 esr);
 int kvm_inject_sea(struct kvm_vcpu *vcpu, bool iabt, u64 addr);
 void kvm_inject_size_fault(struct kvm_vcpu *vcpu);
diff --git a/arch/arm64/kvm/inject_fault.c b/arch/arm64/kvm/inject_fault.c
index dfcd66c655179..7102424a3fa5e 100644
--- a/arch/arm64/kvm/inject_fault.c
+++ b/arch/arm64/kvm/inject_fault.c
@@ -162,12 +162,16 @@ static void inject_abt64(struct kvm_vcpu *vcpu, bool is_iabt, unsigned long addr
 	vcpu_write_sys_reg(vcpu, esr, exception_esr_elx(vcpu));
 }
 
+void kvm_inject_sync(struct kvm_vcpu *vcpu, u64 esr)
+{
+	pend_sync_exception(vcpu);
+	vcpu_write_sys_reg(vcpu, esr, exception_esr_elx(vcpu));
+}
+
 static void inject_undef64(struct kvm_vcpu *vcpu)
 {
 	u64 esr = (ESR_ELx_EC_UNKNOWN << ESR_ELx_EC_SHIFT);
 
-	pend_sync_exception(vcpu);
-
 	/*
 	 * Build an unknown exception, depending on the instruction
 	 * set.
@@ -175,7 +179,7 @@ static void inject_undef64(struct kvm_vcpu *vcpu)
 	if (kvm_vcpu_trap_il_is32bit(vcpu))
 		esr |= ESR_ELx_IL;
 
-	vcpu_write_sys_reg(vcpu, esr, exception_esr_elx(vcpu));
+	kvm_inject_sync(vcpu, esr);
 }
 
 #define DFSR_FSC_EXTABT_LPAE	0x10
-- 
2.47.3

[PATCH v3 4/9] KVM: arm64: Handle FEAT_IDST for sysregs without specific handlers

[Marc Zyngier]

Add a bit of infrastrtcture to triage_sysreg_trap() to handle the
case of registers falling into the Feature ID space that do not
have a local handler.

For these, we can directly apply the FEAT_IDST semantics and inject
an EC=0x18 exception. Otherwise, an UNDEF will do.

Signed-off-by: Marc Zyngier <maz@kernel.org>
---
 arch/arm64/kvm/emulate-nested.c | 20 ++++++++++++++++++++
 1 file changed, 20 insertions(+)

diff --git a/arch/arm64/kvm/emulate-nested.c b/arch/arm64/kvm/emulate-nested.c
index 616eb6ad68701..fac2707221b47 100644
--- a/arch/arm64/kvm/emulate-nested.c
+++ b/arch/arm64/kvm/emulate-nested.c
@@ -2588,6 +2588,26 @@ bool triage_sysreg_trap(struct kvm_vcpu *vcpu, int *sr_index)
 
 		params = esr_sys64_to_params(esr);
 
+		/*
+		 * This implements the pseudocode UnimplementedIDRegister()
+		 * helper for the purpose of fealing with FEAT_IDST.
+		 *
+		 * The Feature ID space is defined as the System register
+		 * space in AArch64 with op0==3, op1=={0, 1, 3}, CRn==0,
+		 * CRm=={0-7}, op2=={0-7}.
+		 */
+		if (params.Op0 == 3 &&
+		    !(params.Op1 & 0b100) && params.Op1 != 2 &&
+		    params.CRn == 0 &&
+		    !(params.CRm & 0b1000)) {
+			if (kvm_has_feat_enum(vcpu->kvm, ID_AA64MMFR2_EL1, IDS, IMP))
+				kvm_inject_sync(vcpu, kvm_vcpu_get_esr(vcpu));
+			else
+				kvm_inject_undefined(vcpu);
+
+			return true;
+		}
+
 		/*
 		 * Check for the IMPDEF range, as per DDI0487 J.a,
 		 * D18.3.2 Reserved encodings for IMPLEMENTATION
-- 
2.47.3

[PATCH v3 5/9] KVM: arm64: Handle CSSIDR2_EL1 and SMIDR_EL1 in a generic way

[Marc Zyngier]

Now that we can handle ID registers using the FEAT_IDST infrastrcuture,
get rid of the handling of CSSIDR2_EL1 and SMIDR_EL1.

Signed-off-by: Marc Zyngier <maz@kernel.org>
---
 arch/arm64/kvm/sys_regs.c | 2 --
 1 file changed, 2 deletions(-)

diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c
index ec3fbe0b8d525..ae1e72df1ed45 100644
--- a/arch/arm64/kvm/sys_regs.c
+++ b/arch/arm64/kvm/sys_regs.c
@@ -3399,8 +3399,6 @@ static const struct sys_reg_desc sys_reg_descs[] = {
 	{ SYS_DESC(SYS_CCSIDR_EL1), access_ccsidr },
 	{ SYS_DESC(SYS_CLIDR_EL1), access_clidr, reset_clidr, CLIDR_EL1,
 	  .set_user = set_clidr, .val = ~CLIDR_EL1_RES0 },
-	{ SYS_DESC(SYS_CCSIDR2_EL1), undef_access },
-	{ SYS_DESC(SYS_SMIDR_EL1), undef_access },
 	IMPLEMENTATION_ID(AIDR_EL1, GENMASK_ULL(63, 0)),
 	{ SYS_DESC(SYS_CSSELR_EL1), access_csselr, reset_unknown, CSSELR_EL1 },
 	ID_FILTERED(CTR_EL0, ctr_el0,
-- 
2.47.3

[PATCH v3 6/9] KVM: arm64: Force trap of GMID_EL1 when the guest doesn't have MTE

[Marc Zyngier]

If our host has MTE, but the guest doesn't, make sure we set HCR_EL2.TID5
to force GMID_EL1 being trapped. Such trap will be handled by the
FEAT_IDST handling.

Reviewed-by: Joey Gouly <joey.gouly@arm.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>
---
 arch/arm64/kvm/sys_regs.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c
index ae1e72df1ed45..2e94c423594eb 100644
--- a/arch/arm64/kvm/sys_regs.c
+++ b/arch/arm64/kvm/sys_regs.c
@@ -5558,6 +5558,8 @@ static void vcpu_set_hcr(struct kvm_vcpu *vcpu)
 
 	if (kvm_has_mte(vcpu->kvm))
 		vcpu->arch.hcr_el2 |= HCR_ATA;
+	else
+		vcpu->arch.hcr_el2 |= HCR_TID5;
 
 	/*
 	 * In the absence of FGT, we cannot independently trap TLBI
-- 
2.47.3

[PATCH v3 7/9] KVM: arm64: pkvm: Add a generic synchronous exception injection primitive

[Marc Zyngier]

Similarly to the "classic" KVM code, pKVM doesn't have an "anything
goes" synchronous exception injection primitive.

Carve one out of the UNDEF injection code.

Signed-off-by: Marc Zyngier <maz@kernel.org>
---
 arch/arm64/kvm/hyp/nvhe/sys_regs.c | 22 +++++++++++++++-------
 1 file changed, 15 insertions(+), 7 deletions(-)

diff --git a/arch/arm64/kvm/hyp/nvhe/sys_regs.c b/arch/arm64/kvm/hyp/nvhe/sys_regs.c
index 107d62921b168..876b36d3d4788 100644
--- a/arch/arm64/kvm/hyp/nvhe/sys_regs.c
+++ b/arch/arm64/kvm/hyp/nvhe/sys_regs.c
@@ -243,16 +243,15 @@ static u64 pvm_calc_id_reg(const struct kvm_vcpu *vcpu, u32 id)
 	}
 }
 
-/*
- * Inject an unknown/undefined exception to an AArch64 guest while most of its
- * sysregs are live.
- */
-static void inject_undef64(struct kvm_vcpu *vcpu)
+static void inject_sync64(struct kvm_vcpu *vcpu, u64 esr)
 {
-	u64 esr = (ESR_ELx_EC_UNKNOWN << ESR_ELx_EC_SHIFT);
-
 	*vcpu_pc(vcpu) = read_sysreg_el2(SYS_ELR);
 	*vcpu_cpsr(vcpu) = read_sysreg_el2(SYS_SPSR);
+
+	/*
+	 * Make sure we have the latest update to VBAR_EL1, as pKVM
+	 * handles traps very early, before sysregs are resync'ed
+	 */
 	__vcpu_assign_sys_reg(vcpu, VBAR_EL1, read_sysreg_el1(SYS_VBAR));
 
 	kvm_pend_exception(vcpu, EXCEPT_AA64_EL1_SYNC);
@@ -265,6 +264,15 @@ static void inject_undef64(struct kvm_vcpu *vcpu)
 	write_sysreg_el2(*vcpu_cpsr(vcpu), SYS_SPSR);
 }
 
+/*
+ * Inject an unknown/undefined exception to an AArch64 guest while most of its
+ * sysregs are live.
+ */
+static void inject_undef64(struct kvm_vcpu *vcpu)
+{
+	inject_sync64(vcpu, (ESR_ELx_EC_UNKNOWN << ESR_ELx_EC_SHIFT));
+}
+
 static u64 read_id_reg(const struct kvm_vcpu *vcpu,
 		       struct sys_reg_desc const *r)
 {
-- 
2.47.3

[PATCH v3 8/9] KVM: arm64: pkvm: Report optional ID register traps with a 0x18 syndrome

[Marc Zyngier]

With FEAT_IDST, unimplemented system registers in the feature ID space
must be reported using EC=0x18 at the closest handling EL, rather than
with an UNDEF.

Most of these system registers are always implemented thanks to their
dependency on FEAT_AA64, except for a set of (currently) three registers:
GMID_EL1 (depending on MTE2), CCSIDR2_EL1 (depending on FEAT_CCIDX),
and SMIDR_EL1 (depending on SME).

For these three registers, report their trap as EC=0x18 if they
end-up trapping into KVM and that FEAT_IDST is implemented in the guest.
Otherwise, just make them UNDEF.

Signed-off-by: Marc Zyngier <maz@kernel.org>
---
 arch/arm64/kvm/hyp/nvhe/sys_regs.c | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

diff --git a/arch/arm64/kvm/hyp/nvhe/sys_regs.c b/arch/arm64/kvm/hyp/nvhe/sys_regs.c
index 876b36d3d4788..efc36645f4b5a 100644
--- a/arch/arm64/kvm/hyp/nvhe/sys_regs.c
+++ b/arch/arm64/kvm/hyp/nvhe/sys_regs.c
@@ -347,6 +347,18 @@ static bool pvm_gic_read_sre(struct kvm_vcpu *vcpu,
 	return true;
 }
 
+static bool pvm_idst_access(struct kvm_vcpu *vcpu,
+			    struct sys_reg_params *p,
+			    const struct sys_reg_desc *r)
+{
+	if (kvm_has_feat_enum(vcpu->kvm, ID_AA64MMFR2_EL1, IDS, NI))
+		inject_undef64(vcpu);
+	else
+		inject_sync64(vcpu, kvm_vcpu_get_esr(vcpu));
+
+	return false;
+}
+
 /* Mark the specified system register as an AArch32 feature id register. */
 #define AARCH32(REG) { SYS_DESC(REG), .access = pvm_access_id_aarch32 }
 
@@ -472,6 +484,9 @@ static const struct sys_reg_desc pvm_sys_reg_descs[] = {
 
 	HOST_HANDLED(SYS_CCSIDR_EL1),
 	HOST_HANDLED(SYS_CLIDR_EL1),
+	{ SYS_DESC(SYS_CCSIDR2_EL1), .access = pvm_idst_access },
+	{ SYS_DESC(SYS_GMID_EL1), .access = pvm_idst_access },
+	{ SYS_DESC(SYS_SMIDR_EL1), .access = pvm_idst_access },
 	HOST_HANDLED(SYS_AIDR_EL1),
 	HOST_HANDLED(SYS_CSSELR_EL1),
 	HOST_HANDLED(SYS_CTR_EL0),
-- 
2.47.3

[PATCH v3 9/9] KVM: arm64: selftests: Add a test for FEAT_IDST

[Marc Zyngier]

Add a very basic test checking that FEAT_IDST actually works for
the {GMID,SMIDR,CSSIDR2}_EL1 registers.

Signed-off-by: Marc Zyngier <maz@kernel.org>
---
 tools/testing/selftests/kvm/Makefile.kvm      |   1 +
 .../testing/selftests/kvm/arm64/idreg-idst.c  | 117 ++++++++++++++++++
 2 files changed, 118 insertions(+)
 create mode 100644 tools/testing/selftests/kvm/arm64/idreg-idst.c

diff --git a/tools/testing/selftests/kvm/Makefile.kvm b/tools/testing/selftests/kvm/Makefile.kvm
index 148d427ff24be..fa44e6d9afc35 100644
--- a/tools/testing/selftests/kvm/Makefile.kvm
+++ b/tools/testing/selftests/kvm/Makefile.kvm
@@ -171,6 +171,7 @@ TEST_GEN_PROGS_arm64 += arm64/vgic_irq
 TEST_GEN_PROGS_arm64 += arm64/vgic_lpi_stress
 TEST_GEN_PROGS_arm64 += arm64/vpmu_counter_access
 TEST_GEN_PROGS_arm64 += arm64/no-vgic-v3
+TEST_GEN_PROGS_arm64 += arm64/idreg-idst
 TEST_GEN_PROGS_arm64 += arm64/kvm-uuid
 TEST_GEN_PROGS_arm64 += access_tracking_perf_test
 TEST_GEN_PROGS_arm64 += arch_timer
diff --git a/tools/testing/selftests/kvm/arm64/idreg-idst.c b/tools/testing/selftests/kvm/arm64/idreg-idst.c
new file mode 100644
index 0000000000000..9ca9f125abdb7
--- /dev/null
+++ b/tools/testing/selftests/kvm/arm64/idreg-idst.c
@@ -0,0 +1,117 @@
+// SPDX-License-Identifier: GPL-2.0
+
+/*
+ * Access all FEAT_IDST-handled registers that depend on more than
+ * just FEAT_AA64, and fail if we don't get an a trap with an 0x18 EC.
+ */
+
+#include <test_util.h>
+#include <kvm_util.h>
+#include <processor.h>
+
+static volatile bool sys64, undef;
+
+#define __check_sr_read(r)					\
+	({							\
+		uint64_t val;					\
+								\
+		sys64 = false;					\
+		undef = false;					\
+		dsb(sy);					\
+		val = read_sysreg_s(SYS_ ## r);			\
+		val;						\
+	})
+
+/* Fatal checks */
+#define check_sr_read(r)					\
+	do {							\
+		__check_sr_read(r);				\
+		__GUEST_ASSERT(!undef, #r " unexpected UNDEF");	\
+		__GUEST_ASSERT(sys64, #r " didn't trap");	\
+	} while(0)
+
+
+static void guest_code(void)
+{
+	check_sr_read(CCSIDR2_EL1);
+	check_sr_read(SMIDR_EL1);
+	check_sr_read(GMID_EL1);
+
+	GUEST_DONE();
+}
+
+static void guest_sys64_handler(struct ex_regs *regs)
+{
+	sys64 = true;
+	undef = false;
+	regs->pc += 4;
+}
+
+static void guest_undef_handler(struct ex_regs *regs)
+{
+	sys64 = false;
+	undef = true;
+	regs->pc += 4;
+}
+
+static void test_run_vcpu(struct kvm_vcpu *vcpu)
+{
+	struct ucall uc;
+
+	do {
+		vcpu_run(vcpu);
+
+		switch (get_ucall(vcpu, &uc)) {
+		case UCALL_ABORT:
+			REPORT_GUEST_ASSERT(uc);
+			break;
+		case UCALL_PRINTF:
+			printf("%s", uc.buffer);
+			break;
+		case UCALL_DONE:
+			break;
+		default:
+			TEST_FAIL("Unknown ucall %lu", uc.cmd);
+		}
+	} while (uc.cmd != UCALL_DONE);
+}
+
+static void test_guest_feat_idst(void)
+{
+	struct kvm_vcpu *vcpu;
+	struct kvm_vm *vm;
+
+	/* This VM has no MTE, no SME, no CCIDX */
+	vm = vm_create_with_one_vcpu(&vcpu, guest_code);
+
+	vm_init_descriptor_tables(vm);
+	vcpu_init_descriptor_tables(vcpu);
+
+	vm_install_sync_handler(vm, VECTOR_SYNC_CURRENT,
+				ESR_ELx_EC_SYS64, guest_sys64_handler);
+	vm_install_sync_handler(vm, VECTOR_SYNC_CURRENT,
+				ESR_ELx_EC_UNKNOWN, guest_undef_handler);
+
+	test_run_vcpu(vcpu);
+
+	kvm_vm_free(vm);
+}
+
+int main(int argc, char *argv[])
+{
+	struct kvm_vcpu *vcpu;
+	struct kvm_vm *vm;
+	uint64_t mmfr2;
+
+	test_disable_default_vgic();
+
+	vm = vm_create_with_one_vcpu(&vcpu, NULL);
+	mmfr2 = vcpu_get_reg(vcpu, KVM_ARM64_SYS_REG(SYS_ID_AA64MMFR2_EL1));
+	__TEST_REQUIRE(FIELD_GET(ID_AA64MMFR2_EL1_IDS, mmfr2) > 0,
+		       "FEAT_IDST not supported");
+	kvm_vm_free(vm);
+
+	test_guest_feat_idst();
+
+	return 0;
+}
-- 
2.47.3

Re: [PATCH v3 1/9] arm64: Repaint ID_AA64MMFR2_EL1.IDS description

[Joey Gouly]

On Thu, Dec 04, 2025 at 09:47:58AM +0000, Marc Zyngier wrote:
> ID_AA64MMFR2_EL1.IDS, as described in the sysreg file, is pretty horrible
> as it diesctly give the ESR value. Repaint it using the usual NI/IMP
typo:   directly
> identifiers to describe the absence/presence of FEAT_IDST.
> 
> Signed-off-by: Marc Zyngier <maz@kernel.org>
Reviewed-by: Joey Gouly <joey.gouly@arm.com>
> ---
>  arch/arm64/kvm/hyp/nvhe/sys_regs.c | 2 +-
>  arch/arm64/tools/sysreg            | 4 ++--
>  2 files changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/arch/arm64/kvm/hyp/nvhe/sys_regs.c b/arch/arm64/kvm/hyp/nvhe/sys_regs.c
> index 82da9b03692d4..107d62921b168 100644
> --- a/arch/arm64/kvm/hyp/nvhe/sys_regs.c
> +++ b/arch/arm64/kvm/hyp/nvhe/sys_regs.c
> @@ -134,7 +134,7 @@ static const struct pvm_ftr_bits pvmid_aa64mmfr2[] = {
>  	MAX_FEAT(ID_AA64MMFR2_EL1, UAO, IMP),
>  	MAX_FEAT(ID_AA64MMFR2_EL1, IESB, IMP),
>  	MAX_FEAT(ID_AA64MMFR2_EL1, AT, IMP),
> -	MAX_FEAT_ENUM(ID_AA64MMFR2_EL1, IDS, 0x18),
> +	MAX_FEAT_ENUM(ID_AA64MMFR2_EL1, IDS, IMP),
>  	MAX_FEAT(ID_AA64MMFR2_EL1, TTL, IMP),
>  	MAX_FEAT(ID_AA64MMFR2_EL1, BBM, 2),
>  	MAX_FEAT(ID_AA64MMFR2_EL1, E0PD, IMP),
> diff --git a/arch/arm64/tools/sysreg b/arch/arm64/tools/sysreg
> index 1c6cdf9d54bba..3261e8791ac03 100644
> --- a/arch/arm64/tools/sysreg
> +++ b/arch/arm64/tools/sysreg
> @@ -2257,8 +2257,8 @@ UnsignedEnum	43:40	FWB
>  	0b0001	IMP
>  EndEnum
>  Enum	39:36	IDS
> -	0b0000	0x0
> -	0b0001	0x18
> +	0b0000	NI
> +	0b0001	IMP
>  EndEnum
>  UnsignedEnum	35:32	AT
>  	0b0000	NI
> -- 
> 2.47.3
> 

Re: [PATCH v3 1/9] arm64: Repaint ID_AA64MMFR2_EL1.IDS description

[Ben Horgan]

Hi Marc,

On 12/4/25 09:47, Marc Zyngier wrote:
> ID_AA64MMFR2_EL1.IDS, as described in the sysreg file, is pretty horrible
> as it diesctly give the ESR value. Repaint it using the usual NI/IMP
> identifiers to describe the absence/presence of FEAT_IDST.
> 
> Signed-off-by: Marc Zyngier <maz@kernel.org>
> ---
>  arch/arm64/kvm/hyp/nvhe/sys_regs.c | 2 +-
>  arch/arm64/tools/sysreg            | 4 ++--
>  2 files changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/arch/arm64/kvm/hyp/nvhe/sys_regs.c b/arch/arm64/kvm/hyp/nvhe/sys_regs.c
> index 82da9b03692d4..107d62921b168 100644
> --- a/arch/arm64/kvm/hyp/nvhe/sys_regs.c
> +++ b/arch/arm64/kvm/hyp/nvhe/sys_regs.c
> @@ -134,7 +134,7 @@ static const struct pvm_ftr_bits pvmid_aa64mmfr2[] = {
>  	MAX_FEAT(ID_AA64MMFR2_EL1, UAO, IMP),
>  	MAX_FEAT(ID_AA64MMFR2_EL1, IESB, IMP),
>  	MAX_FEAT(ID_AA64MMFR2_EL1, AT, IMP),
> -	MAX_FEAT_ENUM(ID_AA64MMFR2_EL1, IDS, 0x18),
> +	MAX_FEAT_ENUM(ID_AA64MMFR2_EL1, IDS, IMP),
>  	MAX_FEAT(ID_AA64MMFR2_EL1, TTL, IMP),
>  	MAX_FEAT(ID_AA64MMFR2_EL1, BBM, 2),
>  	MAX_FEAT(ID_AA64MMFR2_EL1, E0PD, IMP),
> diff --git a/arch/arm64/tools/sysreg b/arch/arm64/tools/sysreg
> index 1c6cdf9d54bba..3261e8791ac03 100644
> --- a/arch/arm64/tools/sysreg
> +++ b/arch/arm64/tools/sysreg
> @@ -2257,8 +2257,8 @@ UnsignedEnum	43:40	FWB
>  	0b0001	IMP
>  EndEnum
>  Enum	39:36	IDS

Should this also be changed to an UnsignedEnum?

> -	0b0000	0x0
> -	0b0001	0x18
> +	0b0000	NI
> +	0b0001	IMP
>  EndEnum
>  UnsignedEnum	35:32	AT
>  	0b0000	NI


Thanks,

Ben

Re: [PATCH v3 1/9] arm64: Repaint ID_AA64MMFR2_EL1.IDS description

[Marc Zyngier]

On Thu, 04 Dec 2025 10:36:54 +0000,
Ben Horgan <ben.horgan@arm.com> wrote:
> 
> Hi Marc,
> 
> On 12/4/25 09:47, Marc Zyngier wrote:
> > ID_AA64MMFR2_EL1.IDS, as described in the sysreg file, is pretty horrible
> > as it diesctly give the ESR value. Repaint it using the usual NI/IMP
> > identifiers to describe the absence/presence of FEAT_IDST.
> > 
> > Signed-off-by: Marc Zyngier <maz@kernel.org>
> > ---
> >  arch/arm64/kvm/hyp/nvhe/sys_regs.c | 2 +-
> >  arch/arm64/tools/sysreg            | 4 ++--
> >  2 files changed, 3 insertions(+), 3 deletions(-)
> > 
> > diff --git a/arch/arm64/kvm/hyp/nvhe/sys_regs.c b/arch/arm64/kvm/hyp/nvhe/sys_regs.c
> > index 82da9b03692d4..107d62921b168 100644
> > --- a/arch/arm64/kvm/hyp/nvhe/sys_regs.c
> > +++ b/arch/arm64/kvm/hyp/nvhe/sys_regs.c
> > @@ -134,7 +134,7 @@ static const struct pvm_ftr_bits pvmid_aa64mmfr2[] = {
> >  	MAX_FEAT(ID_AA64MMFR2_EL1, UAO, IMP),
> >  	MAX_FEAT(ID_AA64MMFR2_EL1, IESB, IMP),
> >  	MAX_FEAT(ID_AA64MMFR2_EL1, AT, IMP),
> > -	MAX_FEAT_ENUM(ID_AA64MMFR2_EL1, IDS, 0x18),
> > +	MAX_FEAT_ENUM(ID_AA64MMFR2_EL1, IDS, IMP),
> >  	MAX_FEAT(ID_AA64MMFR2_EL1, TTL, IMP),
> >  	MAX_FEAT(ID_AA64MMFR2_EL1, BBM, 2),
> >  	MAX_FEAT(ID_AA64MMFR2_EL1, E0PD, IMP),
> > diff --git a/arch/arm64/tools/sysreg b/arch/arm64/tools/sysreg
> > index 1c6cdf9d54bba..3261e8791ac03 100644
> > --- a/arch/arm64/tools/sysreg
> > +++ b/arch/arm64/tools/sysreg
> > @@ -2257,8 +2257,8 @@ UnsignedEnum	43:40	FWB
> >  	0b0001	IMP
> >  EndEnum
> >  Enum	39:36	IDS
> 
> Should this also be changed to an UnsignedEnum?

I'm not sure this brings much when you only have two values. If IDS
was growing a third value, and that there was an actual order in the
numbering scheme, then yes, that'd be useful.

But at this stage, I'm not confident that this is desirable, let alone
necessary.

Thanks,

	M.

-- 
Without deviation from the norm, progress is not possible.

Re: [PATCH v3 8/9] KVM: arm64: pkvm: Report optional ID register traps with a 0x18 syndrome

[Ben Horgan]

Hi Marc,

On 12/4/25 09:48, Marc Zyngier wrote:
> With FEAT_IDST, unimplemented system registers in the feature ID space
> must be reported using EC=0x18 at the closest handling EL, rather than
> with an UNDEF.
> 
> Most of these system registers are always implemented thanks to their
> dependency on FEAT_AA64, except for a set of (currently) three registers:
> GMID_EL1 (depending on MTE2), CCSIDR2_EL1 (depending on FEAT_CCIDX),
> and SMIDR_EL1 (depending on SME).
> 
> For these three registers, report their trap as EC=0x18 if they
> end-up trapping into KVM and that FEAT_IDST is implemented in the guest.
> Otherwise, just make them UNDEF.
> 
> Signed-off-by: Marc Zyngier <maz@kernel.org>
> ---
>  arch/arm64/kvm/hyp/nvhe/sys_regs.c | 15 +++++++++++++++
>  1 file changed, 15 insertions(+)
> 
> diff --git a/arch/arm64/kvm/hyp/nvhe/sys_regs.c b/arch/arm64/kvm/hyp/nvhe/sys_regs.c
> index 876b36d3d4788..efc36645f4b5a 100644
> --- a/arch/arm64/kvm/hyp/nvhe/sys_regs.c
> +++ b/arch/arm64/kvm/hyp/nvhe/sys_regs.c
> @@ -347,6 +347,18 @@ static bool pvm_gic_read_sre(struct kvm_vcpu *vcpu,
>  	return true;
>  }
>  
> +static bool pvm_idst_access(struct kvm_vcpu *vcpu,
> +			    struct sys_reg_params *p,
> +			    const struct sys_reg_desc *r)
> +{
> +	if (kvm_has_feat_enum(vcpu->kvm, ID_AA64MMFR2_EL1, IDS, NI))
> +		inject_undef64(vcpu);
> +	else
> +		inject_sync64(vcpu, kvm_vcpu_get_esr(vcpu));
> +
> +	return false;
> +}
> +

Just wondering, why is the pkvm version register specific? You changed
the non-pkvm from register specific to generic.

>  /* Mark the specified system register as an AArch32 feature id register. */
>  #define AARCH32(REG) { SYS_DESC(REG), .access = pvm_access_id_aarch32 }
>  
> @@ -472,6 +484,9 @@ static const struct sys_reg_desc pvm_sys_reg_descs[] = {
>  
>  	HOST_HANDLED(SYS_CCSIDR_EL1),
>  	HOST_HANDLED(SYS_CLIDR_EL1),
> +	{ SYS_DESC(SYS_CCSIDR2_EL1), .access = pvm_idst_access },
> +	{ SYS_DESC(SYS_GMID_EL1), .access = pvm_idst_access },
> +	{ SYS_DESC(SYS_SMIDR_EL1), .access = pvm_idst_access },
>  	HOST_HANDLED(SYS_AIDR_EL1),
>  	HOST_HANDLED(SYS_CSSELR_EL1),
>  	HOST_HANDLED(SYS_CTR_EL0),

Thanks,

Ben

Re: [PATCH v3 4/9] KVM: arm64: Handle FEAT_IDST for sysregs without specific handlers

[Joey Gouly]

On Thu, Dec 04, 2025 at 09:48:01AM +0000, Marc Zyngier wrote:
> Add a bit of infrastrtcture to triage_sysreg_trap() to handle the
> case of registers falling into the Feature ID space that do not
> have a local handler.
> 
> For these, we can directly apply the FEAT_IDST semantics and inject
> an EC=0x18 exception. Otherwise, an UNDEF will do.
> 
> Signed-off-by: Marc Zyngier <maz@kernel.org>
> ---
>  arch/arm64/kvm/emulate-nested.c | 20 ++++++++++++++++++++
>  1 file changed, 20 insertions(+)
> 
> diff --git a/arch/arm64/kvm/emulate-nested.c b/arch/arm64/kvm/emulate-nested.c
> index 616eb6ad68701..fac2707221b47 100644
> --- a/arch/arm64/kvm/emulate-nested.c
> +++ b/arch/arm64/kvm/emulate-nested.c
> @@ -2588,6 +2588,26 @@ bool triage_sysreg_trap(struct kvm_vcpu *vcpu, int *sr_index)
>  
>  		params = esr_sys64_to_params(esr);
>  
> +		/*
> +		 * This implements the pseudocode UnimplementedIDRegister()
> +		 * helper for the purpose of fealing with FEAT_IDST.
                                            *dealing

> +		 *
> +		 * The Feature ID space is defined as the System register
> +		 * space in AArch64 with op0==3, op1=={0, 1, 3}, CRn==0,
> +		 * CRm=={0-7}, op2=={0-7}.
> +		 */
> +		if (params.Op0 == 3 &&
> +		    !(params.Op1 & 0b100) && params.Op1 != 2 &&
> +		    params.CRn == 0 &&
> +		    !(params.CRm & 0b1000)) {
> +			if (kvm_has_feat_enum(vcpu->kvm, ID_AA64MMFR2_EL1, IDS, IMP))
> +				kvm_inject_sync(vcpu, kvm_vcpu_get_esr(vcpu));
> +			else
> +				kvm_inject_undefined(vcpu);
> +
> +			return true;
> +		}
> +
>  		/*
>  		 * Check for the IMPDEF range, as per DDI0487 J.a,
>  		 * D18.3.2 Reserved encodings for IMPLEMENTATION
> -- 
> 2.47.3
> 

Reviewed-by: Joey Gouly <joey.gouly@arm.com>

Re: [PATCH v3 1/9] arm64: Repaint ID_AA64MMFR2_EL1.IDS description

[Ben Horgan]

Hi Marc,

On 12/4/25 10:48, Marc Zyngier wrote:
> On Thu, 04 Dec 2025 10:36:54 +0000,
> Ben Horgan <ben.horgan@arm.com> wrote:
>>
>> Hi Marc,
>>
>> On 12/4/25 09:47, Marc Zyngier wrote:
>>> ID_AA64MMFR2_EL1.IDS, as described in the sysreg file, is pretty horrible
>>> as it diesctly give the ESR value. Repaint it using the usual NI/IMP
>>> identifiers to describe the absence/presence of FEAT_IDST.
>>>
>>> Signed-off-by: Marc Zyngier <maz@kernel.org>
>>> ---
>>>  arch/arm64/kvm/hyp/nvhe/sys_regs.c | 2 +-
>>>  arch/arm64/tools/sysreg            | 4 ++--
>>>  2 files changed, 3 insertions(+), 3 deletions(-)
>>>
>>> diff --git a/arch/arm64/kvm/hyp/nvhe/sys_regs.c b/arch/arm64/kvm/hyp/nvhe/sys_regs.c
>>> index 82da9b03692d4..107d62921b168 100644
>>> --- a/arch/arm64/kvm/hyp/nvhe/sys_regs.c
>>> +++ b/arch/arm64/kvm/hyp/nvhe/sys_regs.c
>>> @@ -134,7 +134,7 @@ static const struct pvm_ftr_bits pvmid_aa64mmfr2[] = {
>>>  	MAX_FEAT(ID_AA64MMFR2_EL1, UAO, IMP),
>>>  	MAX_FEAT(ID_AA64MMFR2_EL1, IESB, IMP),
>>>  	MAX_FEAT(ID_AA64MMFR2_EL1, AT, IMP),
>>> -	MAX_FEAT_ENUM(ID_AA64MMFR2_EL1, IDS, 0x18),
>>> +	MAX_FEAT_ENUM(ID_AA64MMFR2_EL1, IDS, IMP),
>>>  	MAX_FEAT(ID_AA64MMFR2_EL1, TTL, IMP),
>>>  	MAX_FEAT(ID_AA64MMFR2_EL1, BBM, 2),
>>>  	MAX_FEAT(ID_AA64MMFR2_EL1, E0PD, IMP),
>>> diff --git a/arch/arm64/tools/sysreg b/arch/arm64/tools/sysreg
>>> index 1c6cdf9d54bba..3261e8791ac03 100644
>>> --- a/arch/arm64/tools/sysreg
>>> +++ b/arch/arm64/tools/sysreg
>>> @@ -2257,8 +2257,8 @@ UnsignedEnum	43:40	FWB
>>>  	0b0001	IMP
>>>  EndEnum
>>>  Enum	39:36	IDS
>>
>> Should this also be changed to an UnsignedEnum?
> 
> I'm not sure this brings much when you only have two values. If IDS
> was growing a third value, and that there was an actual order in the
> numbering scheme, then yes, that'd be useful.

Joey just pointed out to me that there is a new third field. Not in the
arm reference manual yet, but mentioned in the xml. I'm unsure if it's
necessary to consider this at the moment though.

https://developer.arm.com/documentation/ddi0601/2025-09/AArch64-Registers/ID-AA64MMFR2-EL1--AArch64-Memory-Model-Feature-Register-2?lang=en

> 
> But at this stage, I'm not confident that this is desirable, let alone
> necessary.
> 
> Thanks,
> 
> 	M.
> 

Thanks,

Ben

Re: [PATCH v3 1/9] arm64: Repaint ID_AA64MMFR2_EL1.IDS description

[Marc Zyngier]

On Thu, 04 Dec 2025 11:13:41 +0000,
Ben Horgan <ben.horgan@arm.com> wrote:
> 
> Hi Marc,
> 
> On 12/4/25 10:48, Marc Zyngier wrote:
> > On Thu, 04 Dec 2025 10:36:54 +0000,
> > Ben Horgan <ben.horgan@arm.com> wrote:
> >>
> >> Hi Marc,
> >>
> >> On 12/4/25 09:47, Marc Zyngier wrote:
> >>> ID_AA64MMFR2_EL1.IDS, as described in the sysreg file, is pretty horrible
> >>> as it diesctly give the ESR value. Repaint it using the usual NI/IMP
> >>> identifiers to describe the absence/presence of FEAT_IDST.
> >>>
> >>> Signed-off-by: Marc Zyngier <maz@kernel.org>
> >>> ---
> >>>  arch/arm64/kvm/hyp/nvhe/sys_regs.c | 2 +-
> >>>  arch/arm64/tools/sysreg            | 4 ++--
> >>>  2 files changed, 3 insertions(+), 3 deletions(-)
> >>>
> >>> diff --git a/arch/arm64/kvm/hyp/nvhe/sys_regs.c b/arch/arm64/kvm/hyp/nvhe/sys_regs.c
> >>> index 82da9b03692d4..107d62921b168 100644
> >>> --- a/arch/arm64/kvm/hyp/nvhe/sys_regs.c
> >>> +++ b/arch/arm64/kvm/hyp/nvhe/sys_regs.c
> >>> @@ -134,7 +134,7 @@ static const struct pvm_ftr_bits pvmid_aa64mmfr2[] = {
> >>>  	MAX_FEAT(ID_AA64MMFR2_EL1, UAO, IMP),
> >>>  	MAX_FEAT(ID_AA64MMFR2_EL1, IESB, IMP),
> >>>  	MAX_FEAT(ID_AA64MMFR2_EL1, AT, IMP),
> >>> -	MAX_FEAT_ENUM(ID_AA64MMFR2_EL1, IDS, 0x18),
> >>> +	MAX_FEAT_ENUM(ID_AA64MMFR2_EL1, IDS, IMP),
> >>>  	MAX_FEAT(ID_AA64MMFR2_EL1, TTL, IMP),
> >>>  	MAX_FEAT(ID_AA64MMFR2_EL1, BBM, 2),
> >>>  	MAX_FEAT(ID_AA64MMFR2_EL1, E0PD, IMP),
> >>> diff --git a/arch/arm64/tools/sysreg b/arch/arm64/tools/sysreg
> >>> index 1c6cdf9d54bba..3261e8791ac03 100644
> >>> --- a/arch/arm64/tools/sysreg
> >>> +++ b/arch/arm64/tools/sysreg
> >>> @@ -2257,8 +2257,8 @@ UnsignedEnum	43:40	FWB
> >>>  	0b0001	IMP
> >>>  EndEnum
> >>>  Enum	39:36	IDS
> >>
> >> Should this also be changed to an UnsignedEnum?
> > 
> > I'm not sure this brings much when you only have two values. If IDS
> > was growing a third value, and that there was an actual order in the
> > numbering scheme, then yes, that'd be useful.
> 
> Joey just pointed out to me that there is a new third field. Not in the
> arm reference manual yet, but mentioned in the xml. I'm unsure if it's
> necessary to consider this at the moment though.
> 
> https://developer.arm.com/documentation/ddi0601/2025-09/AArch64-Registers/ID-AA64MMFR2-EL1--AArch64-Memory-Model-Feature-Register-2?lang=en

Ah, nice catch. In which case I agree that this should become
UnsignedEnum, as the new EL3 feature is a strict superset of 0b0001.

I'll add fix for that on top.

Thanks,

	M.

-- 
Without deviation from the norm, progress is not possible.

Re: [PATCH v3 8/9] KVM: arm64: pkvm: Report optional ID register traps with a 0x18 syndrome

[Marc Zyngier]

On Thu, 04 Dec 2025 10:51:19 +0000,
Ben Horgan <ben.horgan@arm.com> wrote:
> 
> Hi Marc,
> 
> On 12/4/25 09:48, Marc Zyngier wrote:
> > With FEAT_IDST, unimplemented system registers in the feature ID space
> > must be reported using EC=0x18 at the closest handling EL, rather than
> > with an UNDEF.
> > 
> > Most of these system registers are always implemented thanks to their
> > dependency on FEAT_AA64, except for a set of (currently) three registers:
> > GMID_EL1 (depending on MTE2), CCSIDR2_EL1 (depending on FEAT_CCIDX),
> > and SMIDR_EL1 (depending on SME).
> > 
> > For these three registers, report their trap as EC=0x18 if they
> > end-up trapping into KVM and that FEAT_IDST is implemented in the guest.
> > Otherwise, just make them UNDEF.
> > 
> > Signed-off-by: Marc Zyngier <maz@kernel.org>
> > ---
> >  arch/arm64/kvm/hyp/nvhe/sys_regs.c | 15 +++++++++++++++
> >  1 file changed, 15 insertions(+)
> > 
> > diff --git a/arch/arm64/kvm/hyp/nvhe/sys_regs.c b/arch/arm64/kvm/hyp/nvhe/sys_regs.c
> > index 876b36d3d4788..efc36645f4b5a 100644
> > --- a/arch/arm64/kvm/hyp/nvhe/sys_regs.c
> > +++ b/arch/arm64/kvm/hyp/nvhe/sys_regs.c
> > @@ -347,6 +347,18 @@ static bool pvm_gic_read_sre(struct kvm_vcpu *vcpu,
> >  	return true;
> >  }
> >  
> > +static bool pvm_idst_access(struct kvm_vcpu *vcpu,
> > +			    struct sys_reg_params *p,
> > +			    const struct sys_reg_desc *r)
> > +{
> > +	if (kvm_has_feat_enum(vcpu->kvm, ID_AA64MMFR2_EL1, IDS, NI))
> > +		inject_undef64(vcpu);
> > +	else
> > +		inject_sync64(vcpu, kvm_vcpu_get_esr(vcpu));
> > +
> > +	return false;
> > +}
> > +
> 
> Just wondering, why is the pkvm version register specific? You changed
> the non-pkvm from register specific to generic.

Because pKVM relies on a full enumeration of the registers as a design
principle, and refrains from having wide-casting nets as a catch-all.

That's to ensure that there is a "surprise trap" always results in an
UNDEF. Different model from the rest of KVM.

Thanks,

	M.

-- 
Without deviation from the norm, progress is not possible.

Re: [PATCH v3 6/9] KVM: arm64: Force trap of GMID_EL1 when the guest doesn't have MTE

[Yao Yuan]

Hi Marc,
On Thu, Dec 04, 2025 at 09:48:03AM +0800, Marc Zyngier wrote:
> If our host has MTE, but the guest doesn't, make sure we set HCR_EL2.TID5
> to force GMID_EL1 being trapped. Such trap will be handled by the
> FEAT_IDST handling.
>
> Reviewed-by: Joey Gouly <joey.gouly@arm.com>
> Signed-off-by: Marc Zyngier <maz@kernel.org>
> ---
>  arch/arm64/kvm/sys_regs.c | 2 ++
>  1 file changed, 2 insertions(+)
>
> diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c
> index ae1e72df1ed45..2e94c423594eb 100644
> --- a/arch/arm64/kvm/sys_regs.c
> +++ b/arch/arm64/kvm/sys_regs.c
> @@ -5558,6 +5558,8 @@ static void vcpu_set_hcr(struct kvm_vcpu *vcpu)
>
>  	if (kvm_has_mte(vcpu->kvm))
>  		vcpu->arch.hcr_el2 |= HCR_ATA;
> +	else
> +		vcpu->arch.hcr_el2 |= HCR_TID5;

Reviewed-by: Yuan Yao <yaoyuan@linux.alibaba.com>

>
>  	/*
>  	 * In the absence of FGT, we cannot independently trap TLBI
> --
> 2.47.3

Re: [PATCH v3 4/9] KVM: arm64: Handle FEAT_IDST for sysregs without specific handlers

[Yao Yuan]

On Thu, Dec 04, 2025 at 09:48:01AM +0800, Marc Zyngier wrote:
> Add a bit of infrastrtcture to triage_sysreg_trap() to handle the
> case of registers falling into the Feature ID space that do not
> have a local handler.
>
> For these, we can directly apply the FEAT_IDST semantics and inject
> an EC=0x18 exception. Otherwise, an UNDEF will do.
>
> Signed-off-by: Marc Zyngier <maz@kernel.org>
> ---
>  arch/arm64/kvm/emulate-nested.c | 20 ++++++++++++++++++++
>  1 file changed, 20 insertions(+)
>
> diff --git a/arch/arm64/kvm/emulate-nested.c b/arch/arm64/kvm/emulate-nested.c
> index 616eb6ad68701..fac2707221b47 100644
> --- a/arch/arm64/kvm/emulate-nested.c
> +++ b/arch/arm64/kvm/emulate-nested.c
> @@ -2588,6 +2588,26 @@ bool triage_sysreg_trap(struct kvm_vcpu *vcpu, int *sr_index)
>
>  		params = esr_sys64_to_params(esr);
>
> +		/*
> +		 * This implements the pseudocode UnimplementedIDRegister()
> +		 * helper for the purpose of fealing with FEAT_IDST.
> +		 *
> +		 * The Feature ID space is defined as the System register
> +		 * space in AArch64 with op0==3, op1=={0, 1, 3}, CRn==0,
> +		 * CRm=={0-7}, op2=={0-7}.
> +		 */
> +		if (params.Op0 == 3 &&
> +		    !(params.Op1 & 0b100) && params.Op1 != 2 &&
> +		    params.CRn == 0 &&
> +		    !(params.CRm & 0b1000)) {

Hi Marc,

May give a macro/inline function or local variable w/ name like "is_feat_id_space()"
can simplify the long comment here. Others LGTM:

Reviewed-by: Yuan Yao <yaoyuan@linux.alibaba.com>

> +			if (kvm_has_feat_enum(vcpu->kvm, ID_AA64MMFR2_EL1, IDS, IMP))
> +				kvm_inject_sync(vcpu, kvm_vcpu_get_esr(vcpu));
> +			else
> +				kvm_inject_undefined(vcpu);
> +
> +			return true;
> +		}
> +
>  		/*
>  		 * Check for the IMPDEF range, as per DDI0487 J.a,
>  		 * D18.3.2 Reserved encodings for IMPLEMENTATION
> --
> 2.47.3

Re: [PATCH v3 5/9] KVM: arm64: Handle CSSIDR2_EL1 and SMIDR_EL1 in a generic way

[Yao Yuan]

On Thu, Dec 04, 2025 at 09:48:02AM +0800, Marc Zyngier wrote:
> Now that we can handle ID registers using the FEAT_IDST infrastrcuture,
> get rid of the handling of CSSIDR2_EL1 and SMIDR_EL1.
>
> Signed-off-by: Marc Zyngier <maz@kernel.org>
> ---
>  arch/arm64/kvm/sys_regs.c | 2 --
>  1 file changed, 2 deletions(-)
>
> diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c
> index ec3fbe0b8d525..ae1e72df1ed45 100644
> --- a/arch/arm64/kvm/sys_regs.c
> +++ b/arch/arm64/kvm/sys_regs.c
> @@ -3399,8 +3399,6 @@ static const struct sys_reg_desc sys_reg_descs[] = {
>  	{ SYS_DESC(SYS_CCSIDR_EL1), access_ccsidr },
>  	{ SYS_DESC(SYS_CLIDR_EL1), access_clidr, reset_clidr, CLIDR_EL1,
>  	  .set_user = set_clidr, .val = ~CLIDR_EL1_RES0 },
> -	{ SYS_DESC(SYS_CCSIDR2_EL1), undef_access },
> -	{ SYS_DESC(SYS_SMIDR_EL1), undef_access },
Hi Marc,

I checked the arm ARM to make sure these 2 belong to ID space.

Reviewed-by: Yuan Yao <yaoyuan@linux.alibaba.com>

>  	IMPLEMENTATION_ID(AIDR_EL1, GENMASK_ULL(63, 0)),
>  	{ SYS_DESC(SYS_CSSELR_EL1), access_csselr, reset_unknown, CSSELR_EL1 },
>  	ID_FILTERED(CTR_EL0, ctr_el0,
> --
> 2.47.3