From e0ccc45b056d626d4b271820faeedf3837337ceb Mon Sep 17 00:00:00 2001 From: Mark Brown Date: Thu, 17 Apr 2025 00:32:49 +0100 Subject: [PATCH] KVM: arm64: selftests: Add test for SVE host corruption Until recently, the kernel could unexpectedly discard SVE state for a period after a KVM_RUN ioctl, when the guest did not execute any FPSIMD/SVE/SME instructions. We fixed that issue in commit: fbc7e61195e2 ("KVM: arm64: Unconditionally save+flush host FPSIMD/SVE/SME state") Add a test which tries to provoke that issue by manipulating SVE state before/after running a guest which does not execute any FPSIMD/SVE/SME instructions. The test executes a handful of iterations to miminize the risk that the issue is masked by preemption. Signed-off--by: Mark Rutland Signed-off-by: Mark Brown Acked-by: Mark Rutland Link: https://lore.kernel.org/r/20250417-kvm-selftest-sve-signal-v1-1-6330c2f3da0c@kernel.org [maz: Restored MR's SoB, fixed commit message according to MR's write-up] Signed-off-by: Marc Zyngier --- tools/testing/selftests/kvm/Makefile.kvm | 1 + tools/testing/selftests/kvm/arm64/host_sve.c | 127 +++++++++++++++++++ 2 files changed, 128 insertions(+) create mode 100644 tools/testing/selftests/kvm/arm64/host_sve.c diff --git a/tools/testing/selftests/kvm/Makefile.kvm b/tools/testing/selftests/kvm/Makefile.kvm index f62b0a5aba35..d37072054a3d 100644 --- a/tools/testing/selftests/kvm/Makefile.kvm +++ b/tools/testing/selftests/kvm/Makefile.kvm @@ -147,6 +147,7 @@ TEST_GEN_PROGS_arm64 = $(TEST_GEN_PROGS_COMMON) TEST_GEN_PROGS_arm64 += arm64/aarch32_id_regs TEST_GEN_PROGS_arm64 += arm64/arch_timer_edge_cases TEST_GEN_PROGS_arm64 += arm64/debug-exceptions +TEST_GEN_PROGS_arm64 += arm64/host_sve TEST_GEN_PROGS_arm64 += arm64/hypercalls TEST_GEN_PROGS_arm64 += arm64/mmio_abort TEST_GEN_PROGS_arm64 += arm64/page_fault_test diff --git a/tools/testing/selftests/kvm/arm64/host_sve.c b/tools/testing/selftests/kvm/arm64/host_sve.c new file mode 100644 index 000000000000..3826772fd470 --- /dev/null +++ b/tools/testing/selftests/kvm/arm64/host_sve.c @@ -0,0 +1,127 @@ +// SPDX-License-Identifier: GPL-2.0-only + +/* + * Host SVE: Check FPSIMD/SVE/SME save/restore over KVM_RUN ioctls. + * + * Copyright 2025 Arm, Ltd + */ + +#include +#include +#include +#include +#include + +#include "ucall_common.h" + +static void guest_code(void) +{ + for (int i = 0; i < 10; i++) { + GUEST_UCALL_NONE(); + } + + GUEST_DONE(); +} + +void handle_sigill(int sig, siginfo_t *info, void *ctx) +{ + ucontext_t *uctx = ctx; + + printf(" < host signal %d >\n", sig); + + /* + * Skip the UDF + */ + uctx->uc_mcontext.pc += 4; +} + +void register_sigill_handler(void) +{ + struct sigaction sa = { + .sa_sigaction = handle_sigill, + .sa_flags = SA_SIGINFO, + }; + sigaction(SIGILL, &sa, NULL); +} + +static void do_sve_roundtrip(void) +{ + unsigned long before, after; + + /* + * Set all bits in a predicate register, force a save/restore via a + * SIGILL (which handle_sigill() will recover from), then report + * whether the value has changed. + */ + asm volatile( + " .arch_extension sve\n" + " ptrue p0.B\n" + " cntp %[before], p0, p0.B\n" + " udf #0\n" + " cntp %[after], p0, p0.B\n" + : [before] "=r" (before), + [after] "=r" (after) + : + : "p0" + ); + + if (before != after) { + TEST_FAIL("Signal roundtrip discarded predicate bits (%ld => %ld)\n", + before, after); + } else { + printf("Signal roundtrip preserved predicate bits (%ld => %ld)\n", + before, after); + } +} + +static void test_run(void) +{ + struct kvm_vcpu *vcpu; + struct kvm_vm *vm; + struct ucall uc; + bool guest_done = false; + + register_sigill_handler(); + + vm = vm_create_with_one_vcpu(&vcpu, guest_code); + + do_sve_roundtrip(); + + while (!guest_done) { + + printf("Running VCPU...\n"); + vcpu_run(vcpu); + + switch (get_ucall(vcpu, &uc)) { + case UCALL_NONE: + do_sve_roundtrip(); + do_sve_roundtrip(); + break; + case UCALL_DONE: + guest_done = true; + break; + case UCALL_ABORT: + REPORT_GUEST_ASSERT(uc); + break; + default: + TEST_FAIL("Unexpected guest exit"); + } + } + + kvm_vm_free(vm); +} + +int main(void) +{ + /* + * This is testing the host environment, we don't care about + * guest SVE support. + */ + if (!(getauxval(AT_HWCAP) & HWCAP_SVE)) { + printf("SVE not supported\n"); + return KSFT_SKIP; + } + + test_run(); + return 0; +} -- 2.50.1