[PATCH v2 3/5] KVM: arm64: Add context-switch of ACCDATA_EL1

[Fuad Tabba <fuad.tabba@linux.dev>]

From: Marc Zyngier <maz@kernel.org>

Add ACCDATA_EL1 save/restore as part of the EL0 context. This is
conditioned on the guest's view of ID_AA64ISAR1_EL1.LS64 reporting
that this register is supported.

Signed-off-by: Marc Zyngier <maz@kernel.org>
Fixes: 58ce78667a641 ("arm64: Add support for FEAT_{LS64, LS64_V}")
Link: https://lore.kernel.org/r/20240815125959.2097734-5-maz@kernel.org
Cc: stable@vger.kernel.org
[Fuad: rebased; switch ACCDATA_EL1 for guests only, as the host never
 uses it; gate it on a new ARM64_HAS_LS64_ACCDATA capability, since
 in pKVM the host controls a non-protected guest's ID registers, and
 an EL2 access to ACCDATA_EL1 on a CPU without the feature is UNDEFINED]
Signed-off-by: Fuad Tabba <fuad.tabba@linux.dev>
---
 arch/arm64/kernel/cpufeature.c             |  7 +++++++
 arch/arm64/kvm/hyp/include/hyp/sysreg-sr.h | 23 ++++++++++++++++++++++
 arch/arm64/tools/cpucaps                   |  1 +
 3 files changed, 31 insertions(+)

diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
index 32102c3912fa7..b5720c56eebc9 100644
--- a/arch/arm64/kernel/cpufeature.c
+++ b/arch/arm64/kernel/cpufeature.c
@@ -3225,6 +3225,13 @@ static const struct arm64_cpu_capabilities arm64_features[] = {
 		.cpu_enable = cpu_enable_ls64_v,
 		ARM64_CPUID_FIELDS(ID_AA64ISAR1_EL1, LS64, LS64_V)
 	},
+	{
+		.desc = "LS64_ACCDATA",
+		.capability = ARM64_HAS_LS64_ACCDATA,
+		.type = ARM64_CPUCAP_SYSTEM_FEATURE,
+		.matches = has_cpuid_feature,
+		ARM64_CPUID_FIELDS(ID_AA64ISAR1_EL1, LS64, LS64_ACCDATA)
+	},
 #ifdef CONFIG_ARM64_LSUI
 	{
 		.desc = "Unprivileged Load Store Instructions (LSUI)",
diff --git a/arch/arm64/kvm/hyp/include/hyp/sysreg-sr.h b/arch/arm64/kvm/hyp/include/hyp/sysreg-sr.h
index c382848d31947..4a008c8a696ba 100644
--- a/arch/arm64/kvm/hyp/include/hyp/sysreg-sr.h
+++ b/arch/arm64/kvm/hyp/include/hyp/sysreg-sr.h
@@ -17,6 +17,7 @@
 #include <asm/kvm_mmu.h>
 
 static inline bool ctxt_has_s1poe(struct kvm_cpu_context *ctxt);
+static inline bool ctxt_has_accdata(struct kvm_cpu_context *ctxt);
 
 static inline struct kvm_vcpu *ctxt_to_vcpu(struct kvm_cpu_context *ctxt)
 {
@@ -67,6 +68,13 @@ static inline void __sysreg_save_user_state(struct kvm_cpu_context *ctxt)
 {
 	ctxt_sys_reg(ctxt, TPIDR_EL0)	= read_sysreg(tpidr_el0);
 	ctxt_sys_reg(ctxt, TPIDRRO_EL0)	= read_sysreg(tpidrro_el0);
+
+	/*
+	 * Despite the appearances, ACCDATA_EL1 is part of the EL0
+	 * context, as it can only be used using ST64BV0.
+	 */
+	if (ctxt_has_accdata(ctxt))
+		ctxt_sys_reg(ctxt, ACCDATA_EL1)	= read_sysreg_s(SYS_ACCDATA_EL1);
 }
 
 static inline bool ctxt_has_mte(struct kvm_cpu_context *ctxt)
@@ -131,6 +139,18 @@ static inline bool ctxt_has_sctlr2(struct kvm_cpu_context *ctxt)
 	return kvm_has_sctlr2(kern_hyp_va(vcpu->kvm));
 }
 
+static inline bool ctxt_has_accdata(struct kvm_cpu_context *ctxt)
+{
+	struct kvm_vcpu *vcpu;
+
+	/* The host never uses ACCDATA_EL1 */
+	if (!cpus_have_final_cap(ARM64_HAS_LS64_ACCDATA) || !ctxt_is_guest(ctxt))
+		return false;
+
+	vcpu = ctxt_to_vcpu(ctxt);
+	return kvm_has_feat(kern_hyp_va(vcpu->kvm), ID_AA64ISAR1_EL1, LS64, LS64_ACCDATA);
+}
+
 static inline void __sysreg_save_el1_state(struct kvm_cpu_context *ctxt)
 {
 	ctxt_sys_reg(ctxt, SCTLR_EL1)	= read_sysreg_el1(SYS_SCTLR);
@@ -210,6 +230,9 @@ static inline void __sysreg_restore_user_state(struct kvm_cpu_context *ctxt)
 {
 	write_sysreg(ctxt_sys_reg(ctxt, TPIDR_EL0),	tpidr_el0);
 	write_sysreg(ctxt_sys_reg(ctxt, TPIDRRO_EL0),	tpidrro_el0);
+
+	if (ctxt_has_accdata(ctxt))
+		write_sysreg_s(ctxt_sys_reg(ctxt, ACCDATA_EL1), SYS_ACCDATA_EL1);
 }
 
 static inline void __sysreg_restore_el1_state(struct kvm_cpu_context *ctxt,
diff --git a/arch/arm64/tools/cpucaps b/arch/arm64/tools/cpucaps
index 2775ba3359cfe..f01719bbd6037 100644
--- a/arch/arm64/tools/cpucaps
+++ b/arch/arm64/tools/cpucaps
@@ -49,6 +49,7 @@ HAS_LPA2
 HAS_LSE_ATOMICS
 HAS_LS64
 HAS_LS64_V
+HAS_LS64_ACCDATA
 HAS_LSUI
 HAS_MOPS
 HAS_NESTED_VIRT
-- 
2.47.3