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SubjectRe: [PATCH 12/14] arm64: KVM: Add ARCH_WORKAROUND_2 support for guests
On Tue, May 22, 2018 at 04:06:46PM +0100, Marc Zyngier wrote:
> 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>
> Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>

Reviewed-by: Mark Rutland <mark.rutland@arm.com>

Mark.

> ---
> 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 707a1f06dc5d..b0c17d88ed40 100644
> --- a/arch/arm/include/asm/kvm_mmu.h
> +++ b/arch/arm/include/asm/kvm_mmu.h
> @@ -319,6 +319,11 @@ 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 082110993647..eb7a5c2a2bfb 100644
> --- a/arch/arm64/include/asm/kvm_mmu.h
> +++ b/arch/arm64/include/asm/kvm_mmu.h
> @@ -457,6 +457,30 @@ 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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