[RFC PATCH 12/16] KVM: arm64/sve: Context switch the SVE registers

Dave Martin
2018-06-21T14:47:37Z

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 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>
---
arch/arm64/include/asm/kvm_host.h | 2 ++
arch/arm64/kvm/fpsimd.c | 5 +++--
arch/arm64/kvm/hyp/switch.c | 43 ++++++++++++++++++++++++++++++---------
3 files changed, 38 insertions(+), 12 deletions(-)

diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
index f331abf..d2084ae 100644
--- a/arch/arm64/include/asm/kvm_host.h
+++ b/arch/arm64/include/asm/kvm_host.h
@@ -211,6 +211,8 @@ typedef struct kvm_cpu_context kvm_cpu_context_t;

struct kvm_vcpu_arch {
struct kvm_cpu_context ctxt;
+ void *sve_state;
+ unsigned int sve_max_vl;

/* HYP configuration */
u64 hcr_el2;
diff --git a/arch/arm64/kvm/fpsimd.c b/arch/arm64/kvm/fpsimd.c
index 872008c..44cf783 100644
--- a/arch/arm64/kvm/fpsimd.c
+++ b/arch/arm64/kvm/fpsimd.c
@@ -86,10 +86,11 @@ 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_max_vl);
+ 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->arch));
}
}

diff --git a/arch/arm64/kvm/hyp/switch.c b/arch/arm64/kvm/hyp/switch.c
index d496ef5..98df5c1 100644
--- a/arch/arm64/kvm/hyp/switch.c
+++ b/arch/arm64/kvm/hyp/switch.c
@@ -98,8 +98,13 @@ 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->arch))
+ val |= CPACR_EL1_ZEN;
+ } else {
val &= ~CPACR_EL1_FPEN;
+ }

write_sysreg(val, cpacr_el1);

@@ -114,6 +119,7 @@ static void __hyp_text __activate_traps_nvhe(struct kvm_vcpu *vcpu)

val = CPTR_EL2_DEFAULT;
val |= CPTR_EL2_TTA | CPTR_EL2_TZ;
+
if (!update_fp_enabled(vcpu))
val |= CPTR_EL2_TFP;

@@ -329,16 +335,22 @@ static bool __hyp_text __skip_instr(struct kvm_vcpu *vcpu)
}
}

-static bool __hyp_text __hyp_switch_fpsimd(struct kvm_vcpu *vcpu)
+static bool __hyp_text __hyp_switch_fpsimd(struct kvm_vcpu *vcpu,
+ bool guest_has_sve)
{
struct user_fpsimd_state *host_fpsimd = vcpu->arch.host_fpsimd_state;

- if (has_vhe())
- write_sysreg(read_sysreg(cpacr_el1) | CPACR_EL1_FPEN,
- cpacr_el1);
- else
+ if (has_vhe()) {
+ u64 reg = read_sysreg(cpacr_el1) | CPACR_EL1_FPEN;
+
+ if (system_supports_sve() && guest_has_sve)
+ reg |= CPACR_EL1_ZEN;
+
+ write_sysreg(reg, cpacr_el1);
+ } else {
write_sysreg(read_sysreg(cptr_el2) & ~(u64)CPTR_EL2_TFP,
cptr_el2);
+ }

isb();

@@ -361,7 +373,13 @@ static bool __hyp_text __hyp_switch_fpsimd(struct kvm_vcpu *vcpu)
vcpu->arch.flags &= ~KVM_ARM64_FP_HOST;
}

- __fpsimd_restore_state(&vcpu->arch.ctxt.gp_regs.fp_regs);
+ if (system_supports_sve() && guest_has_sve)
+ sve_load_state((char *)vcpu->arch.sve_state +
+ sve_ffr_offset(vcpu->arch.sve_max_vl),
+ &vcpu->arch.ctxt.gp_regs.fp_regs.fpsr,
+ sve_vq_from_vl(vcpu->arch.sve_max_vl) - 1);
+ else
+ __fpsimd_restore_state(&vcpu->arch.ctxt.gp_regs.fp_regs);

/* Skip restoring fpexc32 for AArch64 guests */
if (!(read_sysreg(hcr_el2) & HCR_RW))
@@ -380,6 +398,8 @@ static bool __hyp_text __hyp_switch_fpsimd(struct kvm_vcpu *vcpu)
*/
static bool __hyp_text fixup_guest_exit(struct kvm_vcpu *vcpu, u64 *exit_code)
{
+ bool guest_has_sve;
+
if (ARM_EXCEPTION_CODE(*exit_code) != ARM_EXCEPTION_IRQ)
vcpu->arch.fault.esr_el2 = read_sysreg_el2(esr);

@@ -397,10 +417,13 @@ 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);
+ guest_has_sve = vcpu_has_sve(&vcpu->arch);
+ if ((system_supports_fpsimd() &&
+ kvm_vcpu_trap_get_class(vcpu) == ESR_ELx_EC_FP_ASIMD) ||
+ (guest_has_sve && kvm_vcpu_trap_get_class(vcpu) == ESR_ELx_EC_SVE))
+ return __hyp_switch_fpsimd(vcpu, guest_has_sve);

if (!__populate_fault_info(vcpu))
return true;
--
2.1.4