@@ -1694,31 +1694,6 @@ void fpsimd_signal_preserve_current_state(void)
sve_to_fpsimd(current);
}
-/*
- * Called by KVM when entering the guest.
- */
-void fpsimd_kvm_prepare(void)
-{
- if (!system_supports_sve())
- return;
-
- /*
- * KVM does not save host SVE state since we can only enter
- * the guest from a syscall so the ABI means that only the
- * non-saved SVE state needs to be saved. If we have left
- * SVE enabled for performance reasons then update the task
- * state to be FPSIMD only.
- */
- get_cpu_fpsimd_context();
-
- if (test_and_clear_thread_flag(TIF_SVE)) {
- sve_to_fpsimd(current);
- current->thread.fp_type = FP_STATE_FPSIMD;
- }
-
- put_cpu_fpsimd_context();
-}
-
/*
* Associate current's FPSIMD context with this cpu
* The caller must have ownership of the cpu FPSIMD context before calling
@@ -54,16 +54,18 @@ void kvm_arch_vcpu_load_fp(struct kvm_vcpu *vcpu)
if (!system_supports_fpsimd())
return;
- fpsimd_kvm_prepare();
-
/*
- * We will check TIF_FOREIGN_FPSTATE just before entering the
- * guest in kvm_arch_vcpu_ctxflush_fp() and override this to
- * FP_STATE_FREE if the flag set.
+ * Ensure that any host FPSIMD/SVE/SME state is saved and unbound such
+ * that the host kernel is responsible for restoring this state upon
+ * return to userspace, and the hyp code doesn't need to save anything.
+ *
+ * When the host may use SME, fpsimd_save_and_flush_cpu_state() ensures
+ * that PSTATE.{SM,ZA} == {0,0}.
*/
- *host_data_ptr(fp_owner) = FP_STATE_HOST_OWNED;
- *host_data_ptr(fpsimd_state) = kern_hyp_va(¤t->thread.uw.fpsimd_state);
- *host_data_ptr(fpmr_ptr) = kern_hyp_va(¤t->thread.uw.fpmr);
+ fpsimd_save_and_flush_cpu_state();
+ *host_data_ptr(fp_owner) = FP_STATE_FREE;
+ *host_data_ptr(fpsimd_state) = NULL;
+ *host_data_ptr(fpmr_ptr) = NULL;
host_data_clear_flag(HOST_SVE_ENABLED);
if (read_sysreg(cpacr_el1) & CPACR_EL1_ZEN_EL0EN)
@@ -73,23 +75,6 @@ void kvm_arch_vcpu_load_fp(struct kvm_vcpu *vcpu)
host_data_clear_flag(HOST_SME_ENABLED);
if (read_sysreg(cpacr_el1) & CPACR_EL1_SMEN_EL0EN)
host_data_set_flag(HOST_SME_ENABLED);
-
- /*
- * If PSTATE.SM is enabled then save any pending FP
- * state and disable PSTATE.SM. If we leave PSTATE.SM
- * enabled and the guest does not enable SME via
- * CPACR_EL1.SMEN then operations that should be valid
- * may generate SME traps from EL1 to EL1 which we
- * can't intercept and which would confuse the guest.
- *
- * Do the same for PSTATE.ZA in the case where there
- * is state in the registers which has not already
- * been saved, this is very unlikely to happen.
- */
- if (read_sysreg_s(SYS_SVCR) & (SVCR_SM_MASK | SVCR_ZA_MASK)) {
- *host_data_ptr(fp_owner) = FP_STATE_FREE;
- fpsimd_save_and_flush_cpu_state();
- }
}
/*
There are several problems with the way hyp code lazily saves the host's FPSIMD/SVE state, including: * Host SVE being discarded unexpectedly due to inconsistent configuration of TIF_SVE and CPACR_ELx.ZEN. This has been seen to result in QEMU crashes where SVE is used by memmove(), as reported by Eric Auger: https://issues.redhat.com/browse/RHEL-68997 * Host SVE state is discarded *after* modification by ptrace, which was an unintentional ptrace ABI change introduced with lazy discarding of SVE state. * The host FPMR value can be discarded when running a non-protected VM, where FPMR support is not exposed to a VM, and that VM uses FPSIMD/SVE. In these cases the hyp code does not save the host's FPMR before unbinding the host's FPSIMD/SVE/SME state, leaving a stale value in memory. Avoid these by eagerly saving and "flushing" the host's FPSIMD/SVE/SME state when loading a vCPU such that KVM does not need to save any of the host's FPSIMD/SVE/SME state. For clarity, fpsimd_kvm_prepare() is removed and the necessary call to fpsimd_save_and_flush_cpu_state() is placed in kvm_arch_vcpu_load_fp(). As 'fpsimd_state' and 'fpmr_ptr' should not be used, they are set to NULL; all uses of these will be removed in subsequent patches. Historical problems go back at least as far as v5.17, e.g. erroneous assumptions about TIF_SVE being clear in commit: 8383741ab2e773a9 ("KVM: arm64: Get rid of host SVE tracking/saving") ... and so this eager save+flush probably needs to be backported to ALL stable trees. Fixes: 93ae6b01bafee8fa ("KVM: arm64: Discard any SVE state when entering KVM guests") Fixes: 8c845e2731041f0f ("arm64/sve: Leave SVE enabled on syscall if we don't context switch") Fixes: ef3be86021c3bdf3 ("KVM: arm64: Add save/restore support for FPMR") Reported-by: Eric Auger <eauger@redhat.com> Reported-by: Wilco Dijkstra <wilco.dijkstra@arm.com> Reviewed-by: Mark Brown <broonie@kernel.org> Tested-by: Mark Brown <broonie@kernel.org> Tested-by: Eric Auger <eric.auger@redhat.com> Acked-by: Will Deacon <will@kernel.org> Cc: stable@vger.kernel.org Cc: Catalin Marinas <catalin.marinas@arm.com> Cc: Florian Weimer <fweimer@redhat.com> Cc: Fuad Tabba <tabba@google.com> Cc: Jeremy Linton <jeremy.linton@arm.com> Cc: Marc Zyngier <maz@kernel.org> Cc: Oliver Upton <oliver.upton@linux.dev> Cc: Paolo Bonzini <pbonzini@redhat.com> Signed-off-by: Mark Rutland <mark.rutland@arm.com> --- arch/arm64/kernel/fpsimd.c | 25 ------------------------- arch/arm64/kvm/fpsimd.c | 35 ++++++++++------------------------- 2 files changed, 10 insertions(+), 50 deletions(-)