arm64: KVM: Obey RES0/1 reserved bits when setting CPTR_EL2

Some bits in CPTR are defined as RES1 in the architecture.  Setting
these bits to zero may unintentionally enable future architecture
extensions, allowing guests to use them without supervision by the host.

This would be bad: for forwards compatibility, this patch makes
sure the affected bits are always written with 1, not 0.

This patch only addresses CPTR_EL2.  Initialisation of other system
registers may still need review.

Reviewed-by: Marc Zyngier <marc.zyngier@arm.com>
Signed-off-by: Dave Martin <Dave.Martin@arm.com>
Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>

diff --git a/arch/arm64/include/asm/kvm_arm.h b/arch/arm64/include/asm/kvm_arm.h
index 738a95f93e493e3002ac8749857f8599c5ae3404..bef6e9243c636b2aab05688f79de4f37a00154b3 100644 (file)
--- a/arch/arm64/include/asm/kvm_arm.h
+++ b/arch/arm64/include/asm/kvm_arm.h
@@ -182,6 +182,7 @@
 #define CPTR_EL2_TCPAC (1 << 31)
 #define CPTR_EL2_TTA   (1 << 20)
 #define CPTR_EL2_TFP   (1 << CPTR_EL2_TFP_SHIFT)
+#define CPTR_EL2_DEFAULT       0x000033ff
 
 /* Hyp Debug Configuration Register bits */
 #define MDCR_EL2_TDRA          (1 << 11)

diff --git a/arch/arm64/kvm/hyp/switch.c b/arch/arm64/kvm/hyp/switch.c
index ca8f5a5e2f965748fca28ced482c9c195270e5ab..f0e7bdfae134a727ec7c0ac76466020fdb65e0fb 100644 (file)
--- a/arch/arm64/kvm/hyp/switch.c
+++ b/arch/arm64/kvm/hyp/switch.c
@@ -36,7 +36,11 @@ static void __hyp_text __activate_traps(struct kvm_vcpu *vcpu)
        write_sysreg(val, hcr_el2);
        /* Trap on AArch32 cp15 c15 accesses (EL1 or EL0) */
        write_sysreg(1 << 15, hstr_el2);
-       write_sysreg(CPTR_EL2_TTA | CPTR_EL2_TFP, cptr_el2);
+
+       val = CPTR_EL2_DEFAULT;
+       val |= CPTR_EL2_TTA | CPTR_EL2_TFP;
+       write_sysreg(val, cptr_el2);
+
        write_sysreg(vcpu->arch.mdcr_el2, mdcr_el2);
 }
 
@@ -45,7 +49,7 @@ static void __hyp_text __deactivate_traps(struct kvm_vcpu *vcpu)
        write_sysreg(HCR_RW, hcr_el2);
        write_sysreg(0, hstr_el2);
        write_sysreg(read_sysreg(mdcr_el2) & MDCR_EL2_HPMN_MASK, mdcr_el2);
-       write_sysreg(0, cptr_el2);
+       write_sysreg(CPTR_EL2_DEFAULT, cptr_el2);
 }
 
 static void __hyp_text __activate_vm(struct kvm_vcpu *vcpu)