Re: [PATCH v7 13/27] KVM: arm64/sve: Context switch the SVE registers

Andrew Jones
2019-04-03T20:02:04Z

On Fri, Mar 29, 2019 at 01:00:38PM +0000, Dave Martin wrote:
> In order to give each vcpu its own view of the SVE registers, this
> patch adds context storage via a new sve_state pointer in struct
> vcpu_arch. An additional member sve_max_vl is also added for each
> vcpu, to determine the maximum vector length visible to the guest
> and thus the value to be configured in ZCR_EL2.LEN while the vcpu
> is active. This also determines the layout and size of the storage
> in sve_state, which is read and written by the same backend
> functions that are used for context-switching the SVE state for
> host tasks.
>
> On SVE-enabled vcpus, SVE access traps are now handled by switching
> in the vcpu's SVE context and disabling the trap before returning
> to the guest. On other vcpus, the trap is not handled and an exit
> back to the host occurs, where the handle_sve() fallback path
> reflects an undefined instruction exception back to the guest,
> consistently with the behaviour of non-SVE-capable hardware (as was
> done unconditionally prior to this patch).
>
> No SVE handling is added on non-VHE-only paths, since VHE is an
> architectural and Kconfig prerequisite of SVE.
>
> Signed-off-by: Dave Martin <Dave.Martin@arm.com>
> Reviewed-by: Julien Thierry <julien.thierry@arm.com>
> Tested-by: zhang.lei <zhang.lei@jp.fujitsu.com>
>
> ---
>
> Changes since v5:
>
> * [Julien Thierry, Julien Grall] Commit message typo fixes
>
> * [Mark Rutland] Rename trap_class to hsr_ec, for consistency with
> existing code.
>
> * [Mark Rutland] Simplify condition for refusing to handle an
> FPSIMD/SVE trap, using multiple if () statements for clarity. The
> previous condition was a bit tortuous, and how that the static_key
> checks have been hoisted out, it makes little difference to the
> compiler how we express the condition here.
> ---
> arch/arm64/include/asm/kvm_host.h | 6 ++++
> arch/arm64/kvm/fpsimd.c | 5 +--
> arch/arm64/kvm/hyp/switch.c | 75 +++++++++++++++++++++++++++++----------
> 3 files changed, 66 insertions(+), 20 deletions(-)
>
> diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
> index 22cf484..4fabfd2 100644
> --- a/arch/arm64/include/asm/kvm_host.h
> +++ b/arch/arm64/include/asm/kvm_host.h
> @@ -228,6 +228,8 @@ struct vcpu_reset_state {
>
> struct kvm_vcpu_arch {
> struct kvm_cpu_context ctxt;
> + void *sve_state;
> + unsigned int sve_max_vl;
>
> /* HYP configuration */
> u64 hcr_el2;
> @@ -323,6 +325,10 @@ struct kvm_vcpu_arch {
> bool sysregs_loaded_on_cpu;
> };
>
> +/* Pointer to the vcpu's SVE FFR for sve_{save,load}_state() */
> +#define vcpu_sve_pffr(vcpu) ((void *)((char *)((vcpu)->arch.sve_state) + \
> + sve_ffr_offset((vcpu)->arch.sve_max_vl)))

Maybe an inline function instead?

> +
> /* vcpu_arch flags field values: */
> #define KVM_ARM64_DEBUG_DIRTY (1 << 0)
> #define KVM_ARM64_FP_ENABLED (1 << 1) /* guest FP regs loaded */
> diff --git a/arch/arm64/kvm/fpsimd.c b/arch/arm64/kvm/fpsimd.c
> index 7053bf4..6e3c9c8 100644
> --- a/arch/arm64/kvm/fpsimd.c
> +++ b/arch/arm64/kvm/fpsimd.c
> @@ -87,10 +87,11 @@ void kvm_arch_vcpu_ctxsync_fp(struct kvm_vcpu *vcpu)
>
> if (vcpu->arch.flags & KVM_ARM64_FP_ENABLED) {
> fpsimd_bind_state_to_cpu(&vcpu->arch.ctxt.gp_regs.fp_regs,
> - NULL, SVE_VL_MIN);
> + vcpu->arch.sve_state,
> + vcpu->arch.sve_max_vl);
>
> clear_thread_flag(TIF_FOREIGN_FPSTATE);
> - clear_thread_flag(TIF_SVE);
> + update_thread_flag(TIF_SVE, vcpu_has_sve(vcpu));
> }
> }
>
> diff --git a/arch/arm64/kvm/hyp/switch.c b/arch/arm64/kvm/hyp/switch.c
> index 9d46066..5444b9c 100644
> --- a/arch/arm64/kvm/hyp/switch.c
> +++ b/arch/arm64/kvm/hyp/switch.c
> @@ -100,7 +100,10 @@ static void activate_traps_vhe(struct kvm_vcpu *vcpu)
> val = read_sysreg(cpacr_el1);
> val |= CPACR_EL1_TTA;
> val &= ~CPACR_EL1_ZEN;
> - if (!update_fp_enabled(vcpu)) {
> + if (update_fp_enabled(vcpu)) {
> + if (vcpu_has_sve(vcpu))
> + val |= CPACR_EL1_ZEN;
> + } else {
> val &= ~CPACR_EL1_FPEN;
> __activate_traps_fpsimd32(vcpu);
> }
> @@ -317,16 +320,48 @@ static bool __hyp_text __populate_fault_info(struct kvm_vcpu *vcpu)
> return true;
> }
>
> -static bool __hyp_text __hyp_switch_fpsimd(struct kvm_vcpu *vcpu)
> +/* Check for an FPSIMD/SVE trap and handle as appropriate */
> +static bool __hyp_text __hyp_handle_fpsimd(struct kvm_vcpu *vcpu)
> {
> - struct user_fpsimd_state *host_fpsimd = vcpu->arch.host_fpsimd_state;
> + bool vhe, sve_guest, sve_host;
> + u8 hsr_ec;
>
> - if (has_vhe())
> - write_sysreg(read_sysreg(cpacr_el1) | CPACR_EL1_FPEN,
> - cpacr_el1);
> - else
> + if (!system_supports_fpsimd())
> + return false;
> +
> + if (system_supports_sve()) {
> + sve_guest = vcpu_has_sve(vcpu);
> + sve_host = vcpu->arch.flags & KVM_ARM64_HOST_SVE_IN_USE;
> + vhe = true;
> + } else {
> + sve_guest = false;
> + sve_host = false;
> + vhe = has_vhe();
> + }
> +
> + hsr_ec = kvm_vcpu_trap_get_class(vcpu);
> + if (hsr_ec != ESR_ELx_EC_FP_ASIMD &&
> + hsr_ec != ESR_ELx_EC_SVE)
> + return false;
> +
> + /* Don't handle SVE traps for non-SVE vcpus here: */
> + if (!sve_guest)
> + if (hsr_ec != ESR_ELx_EC_FP_ASIMD)
> + return false;
> +
> + /* Valid trap. Switch the context: */
> +
> + if (vhe) {
> + u64 reg = read_sysreg(cpacr_el1) | CPACR_EL1_FPEN;
> +
> + if (sve_guest)
> + reg |= CPACR_EL1_ZEN;
> +
> + write_sysreg(reg, cpacr_el1);
> + } else {
> write_sysreg(read_sysreg(cptr_el2) & ~(u64)CPTR_EL2_TFP,
> cptr_el2);
> + }
>
> isb();
>
> @@ -335,24 +370,28 @@ static bool __hyp_text __hyp_switch_fpsimd(struct kvm_vcpu *vcpu)
> * In the SVE case, VHE is assumed: it is enforced by
> * Kconfig and kvm_arch_init().
> */
> - if (system_supports_sve() &&
> - (vcpu->arch.flags & KVM_ARM64_HOST_SVE_IN_USE)) {
> + if (sve_host) {
> struct thread_struct *thread = container_of(
> - host_fpsimd,
> + vcpu->arch.host_fpsimd_state,
> struct thread_struct, uw.fpsimd_state);
>
> - sve_save_state(sve_pffr(thread), &host_fpsimd->fpsr);
> + sve_save_state(sve_pffr(thread),
> + &vcpu->arch.host_fpsimd_state->fpsr);
> } else {
> - __fpsimd_save_state(host_fpsimd);
> + __fpsimd_save_state(vcpu->arch.host_fpsimd_state);
> }
>
> vcpu->arch.flags &= ~KVM_ARM64_FP_HOST;
> }
>
> - __fpsimd_restore_state(&vcpu->arch.ctxt.gp_regs.fp_regs);
> -
> - if (vcpu_has_sve(vcpu))
> + if (sve_guest) {
> + sve_load_state(vcpu_sve_pffr(vcpu),
> + &vcpu->arch.ctxt.gp_regs.fp_regs.fpsr,
> + sve_vq_from_vl(vcpu->arch.sve_max_vl) - 1);
> write_sysreg_s(vcpu->arch.ctxt.sys_regs[ZCR_EL1], SYS_ZCR_EL12);
> + } else {
> + __fpsimd_restore_state(&vcpu->arch.ctxt.gp_regs.fp_regs);
> + }
>
> /* Skip restoring fpexc32 for AArch64 guests */
> if (!(read_sysreg(hcr_el2) & HCR_RW))
> @@ -388,10 +427,10 @@ static bool __hyp_text fixup_guest_exit(struct kvm_vcpu *vcpu, u64 *exit_code)
> * and restore the guest context lazily.
> * If FP/SIMD is not implemented, handle the trap and inject an
> * undefined instruction exception to the guest.
> + * Similarly for trapped SVE accesses.
> */
> - if (system_supports_fpsimd() &&
> - kvm_vcpu_trap_get_class(vcpu) == ESR_ELx_EC_FP_ASIMD)
> - return __hyp_switch_fpsimd(vcpu);
> + if (__hyp_handle_fpsimd(vcpu))
> + return true;
>
> if (!__populate_fault_info(vcpu))
> return true;

Reviewed-by: Andrew Jones <drjones@redhat.com>