[RFC/RFT PATCH 03/16] KVM: arm64: Set SCTLR_EL2.DSSBS if SSBD is forcefully disabled and !vhe

[Ard Biesheuvel <ard.biesheuvel@linaro.org>]

From: Will Deacon <will.deacon@arm.com>

When running without VHE, it is necessary to set SCTLR_EL2.DSSBS if SSBD
has been forcefully disabled on the kernel command-line.

Acked-by: Christoffer Dall <christoffer.dall@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
(cherry picked from commit 7c36447ae5a090729e7b129f24705bb231a07e0b)
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
---
 arch/arm64/include/asm/kvm_host.h | 11 +++++++++++
 arch/arm64/kvm/hyp/sysreg-sr.c    | 11 +++++++++++
 2 files changed, 22 insertions(+)

diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
index 6abe4002945f..367b2e0b6d76 100644
--- a/arch/arm64/include/asm/kvm_host.h
+++ b/arch/arm64/include/asm/kvm_host.h
@@ -398,6 +398,8 @@ struct kvm_vcpu *kvm_mpidr_to_vcpu(struct kvm *kvm, unsigned long mpidr);
 
 DECLARE_PER_CPU(kvm_cpu_context_t, kvm_host_cpu_state);
 
+void __kvm_enable_ssbs(void);
+
 static inline void __cpu_init_hyp_mode(phys_addr_t pgd_ptr,
 				       unsigned long hyp_stack_ptr,
 				       unsigned long vector_ptr)
@@ -418,6 +420,15 @@ static inline void __cpu_init_hyp_mode(phys_addr_t pgd_ptr,
 	 */
 	BUG_ON(!static_branch_likely(&arm64_const_caps_ready));
 	__kvm_call_hyp((void *)pgd_ptr, hyp_stack_ptr, vector_ptr, tpidr_el2);
+
+	/*
+	 * Disabling SSBD on a non-VHE system requires us to enable SSBS
+	 * at EL2.
+	 */
+	if (!has_vhe() && this_cpu_has_cap(ARM64_SSBS) &&
+	    arm64_get_ssbd_state() == ARM64_SSBD_FORCE_DISABLE) {
+		kvm_call_hyp(__kvm_enable_ssbs);
+	}
 }
 
 static inline bool kvm_arch_check_sve_has_vhe(void)
diff --git a/arch/arm64/kvm/hyp/sysreg-sr.c b/arch/arm64/kvm/hyp/sysreg-sr.c
index 963d669ae3a2..7414b76191c2 100644
--- a/arch/arm64/kvm/hyp/sysreg-sr.c
+++ b/arch/arm64/kvm/hyp/sysreg-sr.c
@@ -293,3 +293,14 @@ void kvm_vcpu_put_sysregs(struct kvm_vcpu *vcpu)
 
 	vcpu->arch.sysregs_loaded_on_cpu = false;
 }
+
+void __hyp_text __kvm_enable_ssbs(void)
+{
+	u64 tmp;
+
+	asm volatile(
+	"mrs	%0, sctlr_el2\n"
+	"orr	%0, %0, %1\n"
+	"msr	sctlr_el2, %0"
+	: "=&r" (tmp) : "L" (SCTLR_ELx_DSSBS));
+}
-- 
2.20.1


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