[PATCH v2] KVM: arm64: Sync a pVM's control state before CPU_ON reads its endianness

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

pKVM handles a protected guest's PSCI CPU_ON at EL2 before the guest's
EL1 sysregs are saved, so kvm_vcpu_is_be() reads a stale SCTLR_EL1. A
guest that changes SCTLR_EL1.EE and calls CPU_ON before its next exit
to the host starts the target vCPU with the old endianness.

Have CPU_ON sync the caller's PC, PSTATE, VBAR_EL1 and SCTLR_EL1 before
reading its endianness, through a helper factored out of
inject_sync64(), so that both handlers sync the same state.

Fixes: 9d4ec80be2eb4 ("KVM: arm64: Handle PSCI calls for protected VMs at EL2")
Suggested-by: Marc Zyngier <maz@kernel.org>
Signed-off-by: Fuad Tabba <fuad.tabba@linux.dev>
---

Notes:
    Changes in v2:
    - Factor inject_sync64()'s sync into a helper and call it from CPU_ON,
      as Marc suggested. Named pkvm_sync_vcpu_ctrl_state() rather than
      ..._before_exception(), since CPU_ON injects no exception.
    - Subject and message reworded to match.
    
    v1: https://lore.kernel.org/r/20261111082746.1064567-1-fuad.tabba@linux.dev

 arch/arm64/kvm/hyp/include/nvhe/pkvm.h |  1 +
 arch/arm64/kvm/hyp/nvhe/pkvm.c         |  2 ++
 arch/arm64/kvm/hyp/nvhe/sys_regs.c     | 16 ++++++++++------
 3 files changed, 13 insertions(+), 6 deletions(-)

diff --git a/arch/arm64/kvm/hyp/include/nvhe/pkvm.h b/arch/arm64/kvm/hyp/include/nvhe/pkvm.h
index 0261b2bc681f7..5c68c9184bda6 100644
--- a/arch/arm64/kvm/hyp/include/nvhe/pkvm.h
+++ b/arch/arm64/kvm/hyp/include/nvhe/pkvm.h
@@ -133,6 +133,7 @@ bool kvm_handle_pvm_restricted(struct kvm_vcpu *vcpu, u64 *exit_code);
 void kvm_init_pvm_id_regs(struct kvm_vcpu *vcpu);
 void kvm_reset_pvm_sys_regs(struct kvm_vcpu *vcpu);
 int kvm_check_pvm_sysreg_table(void);
+void pkvm_sync_vcpu_ctrl_state(struct kvm_vcpu *vcpu);
 
 int pkvm_reset_vcpu(struct pkvm_hyp_vcpu *hyp_vcpu);
 struct pkvm_hyp_vcpu *pkvm_mpidr_to_hyp_vcpu(struct pkvm_hyp_vm *vm, unsigned long mpidr);
diff --git a/arch/arm64/kvm/hyp/nvhe/pkvm.c b/arch/arm64/kvm/hyp/nvhe/pkvm.c
index fc0475f0877d1..eedc1dd81ee56 100644
--- a/arch/arm64/kvm/hyp/nvhe/pkvm.c
+++ b/arch/arm64/kvm/hyp/nvhe/pkvm.c
@@ -1321,6 +1321,8 @@ static bool pvm_psci_vcpu_on(struct pkvm_hyp_vcpu *hyp_vcpu)
 		goto error;
 	}
 
+	pkvm_sync_vcpu_ctrl_state(&hyp_vcpu->vcpu);
+
 	reset_state = &target->vcpu.arch.reset_state;
 	WRITE_ONCE(reset_state->pc, smccc_get_arg2(&hyp_vcpu->vcpu));
 	WRITE_ONCE(reset_state->r0, smccc_get_arg3(&hyp_vcpu->vcpu));
diff --git a/arch/arm64/kvm/hyp/nvhe/sys_regs.c b/arch/arm64/kvm/hyp/nvhe/sys_regs.c
index 32e82653ebf7e..be785eec2ec96 100644
--- a/arch/arm64/kvm/hyp/nvhe/sys_regs.c
+++ b/arch/arm64/kvm/hyp/nvhe/sys_regs.c
@@ -254,17 +254,21 @@ static u64 pvm_calc_id_reg(const struct kvm_vcpu *vcpu, u32 id)
 	}
 }
 
-static void inject_sync64(struct kvm_vcpu *vcpu, u64 esr)
+/*
+ * pKVM handles some exits at EL2 before it saves the guest's EL1 state, so
+ * sync the copies that exception injection and PSCI CPU_ON read.
+ */
+void pkvm_sync_vcpu_ctrl_state(struct kvm_vcpu *vcpu)
 {
 	*vcpu_pc(vcpu) = read_sysreg_el2(SYS_ELR);
 	*vcpu_cpsr(vcpu) = read_sysreg_el2(SYS_SPSR);
-
-	/*
-	 * Sync VBAR_EL1 and SCTLR_EL1, both read by enter_exception64(),
-	 * as pKVM handles traps before sysregs are resync'ed.
-	 */
 	__vcpu_assign_sys_reg(vcpu, VBAR_EL1, read_sysreg_el1(SYS_VBAR));
 	__vcpu_assign_sys_reg(vcpu, SCTLR_EL1, read_sysreg_el1(SYS_SCTLR));
+}
+
+static void inject_sync64(struct kvm_vcpu *vcpu, u64 esr)
+{
+	pkvm_sync_vcpu_ctrl_state(vcpu);
 
 	kvm_pend_exception(vcpu, EXCEPT_AA64_EL1_SYNC);
 

base-commit: 7475ea8b58616b33c04afb976cf0fbaad9dd63fb
-- 
2.47.3