In non-protected KVM modes, while the guest FPSIMD/SVE/SME state is live on the
CPU, the host's active SVE VL may differ from the guest's maximum SVE VL:
* For VHE hosts, when a VM uses NV, ZCR_EL2 contains a value constrained
by the guest hypervisor, which may be less than or equal to that
guest's maximum VL.
Note: in this case the value of ZCR_EL1 is immaterial due to E2H.
* For nVHE/hVHE hosts, ZCR_EL1 contains a value written by the guest,
which may be less than or greater than the guest's maximum VL.
Note: in this case hyp code traps host SVE usage and lazily restores
ZCR_EL2 to the host's maximum VL, which may be greater than the
guest's maximum VL.
This can be the case between exiting a guest and kvm_arch_vcpu_put_fp().
If a softirq is taken during this period and the softirq handler tries
to use kernel-mode NEON, then the kernel will fail to save the guest's
FPSIMD/SVE state, and will pend a SIGKILL for the current thread.
This happens because kvm_arch_vcpu_ctxsync_fp() binds the guest's live
FPSIMD/SVE state with the guest's maximum SVE VL, and
fpsimd_save_user_state() verifies that the live SVE VL is as expected
before attempting to save the register state:
| if (WARN_ON(sve_get_vl() != vl)) {
| force_signal_inject(SIGKILL, SI_KERNEL, 0, 0);
| return;
| }
Fix this and make this a bit easier to reason about by always eagerly
switching ZCR_EL{1,2} at hyp during guest<->host transitions. With this
happening, there's no need to trap host SVE usage, and the nVHE/nVHE
__deactivate_cptr_traps() logic can be simplified to enable host access
to all present FPSIMD/SVE/SME features.
In protected nVHE/hVHE modes, the host's state is always saved/restored
by hyp, and the guest's state is saved prior to exit to the host, so
from the host's PoV the guest never has live FPSIMD/SVE/SME state, and
the host's ZCR_EL1 is never clobbered by hyp.
Fixes: 8c8010d69c132273 ("KVM: arm64: Save/restore SVE state for nVHE")
Fixes: 2e3cf82063a00ea0 ("KVM: arm64: nv: Ensure correct VL is loaded before saving SVE state")
Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Reviewed-by: Mark Brown <broonie@kernel.org>
Tested-by: Mark Brown <broonie@kernel.org>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Fuad Tabba <tabba@google.com>
Cc: Marc Zyngier <maz@kernel.org>
Cc: Oliver Upton <oliver.upton@linux.dev>
Cc: Will Deacon <will@kernel.org>
Reviewed-by: Oliver Upton <oliver.upton@linux.dev>
Link: https://lore.kernel.org/r/20250210195226.1215254-9-mark.rutland@arm.com
Signed-off-by: Marc Zyngier <maz@kernel.org>
local_irq_save(flags);
if (guest_owns_fp_regs()) {
- if (vcpu_has_sve(vcpu)) {
- u64 zcr = read_sysreg_el1(SYS_ZCR);
-
- /*
- * If the vCPU is in the hyp context then ZCR_EL1 is
- * loaded with its vEL2 counterpart.
- */
- __vcpu_sys_reg(vcpu, vcpu_sve_zcr_elx(vcpu)) = zcr;
-
- /*
- * Restore the VL that was saved when bound to the CPU,
- * which is the maximum VL for the guest. Because the
- * layout of the data when saving the sve state depends
- * on the VL, we need to use a consistent (i.e., the
- * maximum) VL.
- * Note that this means that at guest exit ZCR_EL1 is
- * not necessarily the same as on guest entry.
- *
- * ZCR_EL2 holds the guest hypervisor's VL when running
- * a nested guest, which could be smaller than the
- * max for the vCPU. Similar to above, we first need to
- * switch to a VL consistent with the layout of the
- * vCPU's SVE state. KVM support for NV implies VHE, so
- * using the ZCR_EL1 alias is safe.
- */
- if (!has_vhe() || (vcpu_has_nv(vcpu) && !is_hyp_ctxt(vcpu)))
- sve_cond_update_zcr_vq(vcpu_sve_max_vq(vcpu) - 1,
- SYS_ZCR_EL1);
- }
-
/*
* Flush (save and invalidate) the fpsimd/sve state so that if
* the host tries to use fpsimd/sve, it's not using stale data
alternative_else_nop_endif
mrs x1, isr_el1
cbz x1, 1f
+
+ // Ensure that __guest_enter() always provides a context
+ // synchronization event so that callers don't need ISBs for anything
+ // that would usually be synchonized by the ERET.
+ isb
mov x0, #ARM_EXCEPTION_IRQ
ret
true);
}
+static inline void fpsimd_lazy_switch_to_guest(struct kvm_vcpu *vcpu)
+{
+ u64 zcr_el1, zcr_el2;
+
+ if (!guest_owns_fp_regs())
+ return;
+
+ if (vcpu_has_sve(vcpu)) {
+ /* A guest hypervisor may restrict the effective max VL. */
+ if (vcpu_has_nv(vcpu) && !is_hyp_ctxt(vcpu))
+ zcr_el2 = __vcpu_sys_reg(vcpu, ZCR_EL2);
+ else
+ zcr_el2 = vcpu_sve_max_vq(vcpu) - 1;
+
+ write_sysreg_el2(zcr_el2, SYS_ZCR);
+
+ zcr_el1 = __vcpu_sys_reg(vcpu, vcpu_sve_zcr_elx(vcpu));
+ write_sysreg_el1(zcr_el1, SYS_ZCR);
+ }
+}
+
+static inline void fpsimd_lazy_switch_to_host(struct kvm_vcpu *vcpu)
+{
+ u64 zcr_el1, zcr_el2;
+
+ if (!guest_owns_fp_regs())
+ return;
+
+ /*
+ * When the guest owns the FP regs, we know that guest+hyp traps for
+ * any FPSIMD/SVE/SME features exposed to the guest have been disabled
+ * by either fpsimd_lazy_switch_to_guest() or kvm_hyp_handle_fpsimd()
+ * prior to __guest_entry(). As __guest_entry() guarantees a context
+ * synchronization event, we don't need an ISB here to avoid taking
+ * traps for anything that was exposed to the guest.
+ */
+ if (vcpu_has_sve(vcpu)) {
+ zcr_el1 = read_sysreg_el1(SYS_ZCR);
+ __vcpu_sys_reg(vcpu, vcpu_sve_zcr_elx(vcpu)) = zcr_el1;
+
+ /*
+ * The guest's state is always saved using the guest's max VL.
+ * Ensure that the host has the guest's max VL active such that
+ * the host can save the guest's state lazily, but don't
+ * artificially restrict the host to the guest's max VL.
+ */
+ if (has_vhe()) {
+ zcr_el2 = vcpu_sve_max_vq(vcpu) - 1;
+ write_sysreg_el2(zcr_el2, SYS_ZCR);
+ } else {
+ zcr_el2 = sve_vq_from_vl(kvm_host_sve_max_vl) - 1;
+ write_sysreg_el2(zcr_el2, SYS_ZCR);
+
+ zcr_el1 = vcpu_sve_max_vq(vcpu) - 1;
+ write_sysreg_el1(zcr_el1, SYS_ZCR);
+ }
+ }
+}
+
static void kvm_hyp_save_fpsimd_host(struct kvm_vcpu *vcpu)
{
/*
*/
#include <hyp/adjust_pc.h>
+#include <hyp/switch.h>
#include <asm/pgtable-types.h>
#include <asm/kvm_asm.h>
sync_hyp_vcpu(hyp_vcpu);
} else {
+ struct kvm_vcpu *vcpu = kern_hyp_va(host_vcpu);
+
/* The host is fully trusted, run its vCPU directly. */
- ret = __kvm_vcpu_run(kern_hyp_va(host_vcpu));
+ fpsimd_lazy_switch_to_guest(vcpu);
+ ret = __kvm_vcpu_run(vcpu);
+ fpsimd_lazy_switch_to_host(vcpu);
}
out:
cpu_reg(host_ctxt, 1) = ret;
case ESR_ELx_EC_SMC64:
handle_host_smc(host_ctxt);
break;
- case ESR_ELx_EC_SVE:
- cpacr_clear_set(0, CPACR_EL1_ZEN);
- isb();
- sve_cond_update_zcr_vq(sve_vq_from_vl(kvm_host_sve_max_vl) - 1,
- SYS_ZCR_EL2);
- break;
case ESR_ELx_EC_IABT_LOW:
case ESR_ELx_EC_DABT_LOW:
handle_host_mem_abort(host_ctxt);
static void __deactivate_cptr_traps(struct kvm_vcpu *vcpu)
{
- struct kvm *kvm = kern_hyp_va(vcpu->kvm);
-
if (has_hvhe()) {
u64 val = CPACR_EL1_FPEN;
- if (!kvm_has_sve(kvm) || !guest_owns_fp_regs())
+ if (cpus_have_final_cap(ARM64_SVE))
val |= CPACR_EL1_ZEN;
if (cpus_have_final_cap(ARM64_SME))
val |= CPACR_EL1_SMEN;
} else {
u64 val = CPTR_NVHE_EL2_RES1;
- if (kvm_has_sve(kvm) && guest_owns_fp_regs())
+ if (!cpus_have_final_cap(ARM64_SVE))
val |= CPTR_EL2_TZ;
if (!cpus_have_final_cap(ARM64_SME))
val |= CPTR_EL2_TSM;
sysreg_save_host_state_vhe(host_ctxt);
+ fpsimd_lazy_switch_to_guest(vcpu);
+
/*
* Note that ARM erratum 1165522 requires us to configure both stage 1
* and stage 2 translation for the guest context before we clear
__deactivate_traps(vcpu);
+ fpsimd_lazy_switch_to_host(vcpu);
+
sysreg_restore_host_state_vhe(host_ctxt);
if (guest_owns_fp_regs())
projects / users / dwmw2 / linux.git / commitdiff