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Subject[PATCH v2 12/17] arm64: KVM: Add ARCH_WORKAROUND_2 support for guests
Date
In order to offer ARCH_WORKAROUND_2 support to guests, we need
a bit of infrastructure.

Let's add a flag indicating whether or not the guest uses
SSBD mitigation. Depending on the state of this flag, allow
KVM to disable ARCH_WORKAROUND_2 before entering the guest,
and enable it when exiting it.

Reviewed-by: Christoffer Dall <christoffer.dall@arm.com>
Reviewed-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
---
arch/arm/include/asm/kvm_mmu.h | 5 +++++
arch/arm64/include/asm/kvm_asm.h | 3 +++
arch/arm64/include/asm/kvm_host.h | 3 +++
arch/arm64/include/asm/kvm_mmu.h | 24 ++++++++++++++++++++++
arch/arm64/kvm/hyp/switch.c | 42 +++++++++++++++++++++++++++++++++++++++
virt/kvm/arm/arm.c | 4 ++++
6 files changed, 81 insertions(+)

diff --git a/arch/arm/include/asm/kvm_mmu.h b/arch/arm/include/asm/kvm_mmu.h
index f675162663f0..d2eb24eccf8f 100644
--- a/arch/arm/include/asm/kvm_mmu.h
+++ b/arch/arm/include/asm/kvm_mmu.h
@@ -335,6 +335,11 @@ static inline int kvm_map_vectors(void)
return 0;
}

+static inline int hyp_map_aux_data(void)
+{
+ return 0;
+}
+
#define kvm_phys_to_vttbr(addr) (addr)

#endif /* !__ASSEMBLY__ */
diff --git a/arch/arm64/include/asm/kvm_asm.h b/arch/arm64/include/asm/kvm_asm.h
index fefd8cf42c35..d4fbb1356c4c 100644
--- a/arch/arm64/include/asm/kvm_asm.h
+++ b/arch/arm64/include/asm/kvm_asm.h
@@ -33,6 +33,9 @@
#define KVM_ARM64_DEBUG_DIRTY_SHIFT 0
#define KVM_ARM64_DEBUG_DIRTY (1 << KVM_ARM64_DEBUG_DIRTY_SHIFT)

+#define VCPU_WORKAROUND_2_FLAG_SHIFT 0
+#define VCPU_WORKAROUND_2_FLAG (_AC(1, UL) << VCPU_WORKAROUND_2_FLAG_SHIFT)
+
/* Translate a kernel address of @sym into its equivalent linear mapping */
#define kvm_ksym_ref(sym) \
({ \
diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
index 469de8acd06f..9bef3f69bdcd 100644
--- a/arch/arm64/include/asm/kvm_host.h
+++ b/arch/arm64/include/asm/kvm_host.h
@@ -216,6 +216,9 @@ struct kvm_vcpu_arch {
/* Exception Information */
struct kvm_vcpu_fault_info fault;

+ /* State of various workarounds, see kvm_asm.h for bit assignment */
+ u64 workaround_flags;
+
/* Guest debug state */
u64 debug_flags;

diff --git a/arch/arm64/include/asm/kvm_mmu.h b/arch/arm64/include/asm/kvm_mmu.h
index 6128992c2ded..e3b2ad7dd40a 100644
--- a/arch/arm64/include/asm/kvm_mmu.h
+++ b/arch/arm64/include/asm/kvm_mmu.h
@@ -473,6 +473,30 @@ static inline int kvm_map_vectors(void)
}
#endif

+#ifdef CONFIG_ARM64_SSBD
+DECLARE_PER_CPU_READ_MOSTLY(u64, arm64_ssbd_callback_required);
+
+static inline int hyp_map_aux_data(void)
+{
+ int cpu, err;
+
+ for_each_possible_cpu(cpu) {
+ u64 *ptr;
+
+ ptr = per_cpu_ptr(&arm64_ssbd_callback_required, cpu);
+ err = create_hyp_mappings(ptr, ptr + 1, PAGE_HYP);
+ if (err)
+ return err;
+ }
+ return 0;
+}
+#else
+static inline int hyp_map_aux_data(void)
+{
+ return 0;
+}
+#endif
+
#define kvm_phys_to_vttbr(addr) phys_to_ttbr(addr)

#endif /* __ASSEMBLY__ */
diff --git a/arch/arm64/kvm/hyp/switch.c b/arch/arm64/kvm/hyp/switch.c
index d9645236e474..c50cedc447f1 100644
--- a/arch/arm64/kvm/hyp/switch.c
+++ b/arch/arm64/kvm/hyp/switch.c
@@ -15,6 +15,7 @@
* along with this program. If not, see <http://www.gnu.org/licenses/>.
*/

+#include <linux/arm-smccc.h>
#include <linux/types.h>
#include <linux/jump_label.h>
#include <uapi/linux/psci.h>
@@ -389,6 +390,39 @@ static bool __hyp_text fixup_guest_exit(struct kvm_vcpu *vcpu, u64 *exit_code)
return false;
}

+static inline bool __hyp_text __needs_ssbd_off(struct kvm_vcpu *vcpu)
+{
+ if (!cpus_have_const_cap(ARM64_SSBD))
+ return false;
+
+ return !(vcpu->arch.workaround_flags & VCPU_WORKAROUND_2_FLAG);
+}
+
+static void __hyp_text __set_guest_arch_workaround_state(struct kvm_vcpu *vcpu)
+{
+#ifdef CONFIG_ARM64_SSBD
+ /*
+ * The host runs with the workaround always present. If the
+ * guest wants it disabled, so be it...
+ */
+ if (__needs_ssbd_off(vcpu) &&
+ __hyp_this_cpu_read(arm64_ssbd_callback_required))
+ arm_smccc_1_1_smc(ARM_SMCCC_ARCH_WORKAROUND_2, 0, NULL);
+#endif
+}
+
+static void __hyp_text __set_host_arch_workaround_state(struct kvm_vcpu *vcpu)
+{
+#ifdef CONFIG_ARM64_SSBD
+ /*
+ * If the guest has disabled the workaround, bring it back on.
+ */
+ if (__needs_ssbd_off(vcpu) &&
+ __hyp_this_cpu_read(arm64_ssbd_callback_required))
+ arm_smccc_1_1_smc(ARM_SMCCC_ARCH_WORKAROUND_2, 1, NULL);
+#endif
+}
+
/* Switch to the guest for VHE systems running in EL2 */
int kvm_vcpu_run_vhe(struct kvm_vcpu *vcpu)
{
@@ -409,6 +443,8 @@ int kvm_vcpu_run_vhe(struct kvm_vcpu *vcpu)
sysreg_restore_guest_state_vhe(guest_ctxt);
__debug_switch_to_guest(vcpu);

+ __set_guest_arch_workaround_state(vcpu);
+
do {
/* Jump in the fire! */
exit_code = __guest_enter(vcpu, host_ctxt);
@@ -416,6 +452,8 @@ int kvm_vcpu_run_vhe(struct kvm_vcpu *vcpu)
/* And we're baaack! */
} while (fixup_guest_exit(vcpu, &exit_code));

+ __set_host_arch_workaround_state(vcpu);
+
fp_enabled = fpsimd_enabled_vhe();

sysreg_save_guest_state_vhe(guest_ctxt);
@@ -465,6 +503,8 @@ int __hyp_text __kvm_vcpu_run_nvhe(struct kvm_vcpu *vcpu)
__sysreg_restore_state_nvhe(guest_ctxt);
__debug_switch_to_guest(vcpu);

+ __set_guest_arch_workaround_state(vcpu);
+
do {
/* Jump in the fire! */
exit_code = __guest_enter(vcpu, host_ctxt);
@@ -472,6 +512,8 @@ int __hyp_text __kvm_vcpu_run_nvhe(struct kvm_vcpu *vcpu)
/* And we're baaack! */
} while (fixup_guest_exit(vcpu, &exit_code));

+ __set_host_arch_workaround_state(vcpu);
+
fp_enabled = __fpsimd_enabled_nvhe();

__sysreg_save_state_nvhe(guest_ctxt);
diff --git a/virt/kvm/arm/arm.c b/virt/kvm/arm/arm.c
index a4c1b76240df..2d9b4795edb2 100644
--- a/virt/kvm/arm/arm.c
+++ b/virt/kvm/arm/arm.c
@@ -1490,6 +1490,10 @@ static int init_hyp_mode(void)
}
}

+ err = hyp_map_aux_data();
+ if (err)
+ kvm_err("Cannot map host auxilary data: %d\n", err);
+
return 0;

out_err:
--
2.14.2
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