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Thu, 05 Nov 2026 09:59:05 -0800 (PST) Received: from localhost ([12.55.13.134]) by smtp.gmail.com with ESMTPSA id 46e09a7af769-85ef3e603b9sm5021990a34.20.2026.11.05.09.59.05 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 05 Nov 2026 09:59:05 -0800 (PST) Date: Thu, 5 Nov 2026 11:59:04 -0600 From: Andy Chiu To: Nickolai Zeldovich Cc: Paul Walmsley , Palmer Dabbelt , Albert Ou , Alexandre Ghiti , Andy Chiu , Guobin Zhang , Deepak Gupta , Shuah Khan , linux-riscv@lists.infradead.org, linux-kselftest@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v2 2/2] selftests: riscv: test FP state restore when rt_sigreturn() faults Message-ID: References: <20261031161826.858908-1-nickolai@csail.mit.edu> <20261031161826.858908-3-nickolai@csail.mit.edu> X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20261031161826.858908-3-nickolai@csail.mit.edu> Hi Nickolai, On Sat, Oct 31, 2026 at 12:18:26PM -0400, Nickolai Zeldovich wrote: > Add a test for the previous patch: the signal frame sits on a > userfaultfd page that the handler drops after dirtying the FP > registers, so rt_sigreturn() sleeps in the middle of copying the FP > registers from the frame. The interrupted code must get its own > registers back. > > The test is skipped without the D extension or when userfaultfd is not > available to the caller. > The test is failing on qemu, with or without the patch applied. > Signed-off-by: Nickolai Zeldovich > --- > .../selftests/riscv/sigreturn/.gitignore | 1 + > .../selftests/riscv/sigreturn/Makefile | 5 +- > .../selftests/riscv/sigreturn/fp_restore.c | 146 ++++++++++++++++++ > 3 files changed, 151 insertions(+), 1 deletion(-) > create mode 100644 tools/testing/selftests/riscv/sigreturn/fp_restore.c > > diff --git a/tools/testing/selftests/riscv/sigreturn/.gitignore b/tools/testing/selftests/riscv/sigreturn/.gitignore > index 35002b8ae780..8ed282ecb618 100644 > --- a/tools/testing/selftests/riscv/sigreturn/.gitignore > +++ b/tools/testing/selftests/riscv/sigreturn/.gitignore > @@ -1 +1,2 @@ > +fp_restore > sigreturn > diff --git a/tools/testing/selftests/riscv/sigreturn/Makefile b/tools/testing/selftests/riscv/sigreturn/Makefile > index 8c77508641f3..ac7ae7a7c2ae 100644 > --- a/tools/testing/selftests/riscv/sigreturn/Makefile > +++ b/tools/testing/selftests/riscv/sigreturn/Makefile > @@ -4,9 +4,12 @@ > > CFLAGS += -I$(top_srcdir)/tools/include > > -TEST_GEN_PROGS := sigreturn > +TEST_GEN_PROGS := sigreturn fp_restore > > include ../../lib.mk > > $(OUTPUT)/sigreturn: sigreturn.c > $(CC) -static -o $@ $(CFLAGS) $(LDFLAGS) $^ > + > +$(OUTPUT)/fp_restore: fp_restore.c > + $(CC) -static -pthread -o $@ $(CFLAGS) $(LDFLAGS) $^ > diff --git a/tools/testing/selftests/riscv/sigreturn/fp_restore.c b/tools/testing/selftests/riscv/sigreturn/fp_restore.c > new file mode 100644 > index 000000000000..1a56684c5f28 > --- /dev/null > +++ b/tools/testing/selftests/riscv/sigreturn/fp_restore.c > @@ -0,0 +1,146 @@ > +// SPDX-License-Identifier: GPL-2.0-only > +/* > + * Check that rt_sigreturn() restores the FP registers from the signal > + * frame when the copy of the frame sleeps on a page fault while the > + * handler's FP state is dirty. The frame is placed on a userfaultfd > + * page that the handler drops, so the copy faults after f0-f15. > + */ > +#include > +#include > +#include > +#include > +#include > +#include > +#include > +#include > +#include > +#include > +#include > +#include > +#include > +#include "kselftest_harness.h" > + > +#define PAGE 4096UL > +#define STACK_SIZE 65536UL > +/* the page boundary falls this far into the FP image, after f0-f15 */ > +#define SPLIT 128 > + > +#define F0_15 "0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15" > +/* caller-saved only, so the handler's epilogue does not reload them */ > +#define HANDLER_REGS "0, 1, 2, 3, 4, 5, 6, 7, 10, 11, 12, 13, 14, 15" > + > +static uint64_t pattern[16], handler_pattern[16]; > +static void *saved; > +static int placed; > + > +static void handler(int sig, siginfo_t *si, void *context) > +{ > + ucontext_t *uc = context; > + unsigned long split = (unsigned long)&uc->uc_mcontext.__fpregs + SPLIT; > + > + placed = !(split & (PAGE - 1)); > + if (placed) { > + /* rt_sigreturn() will fault on this page and wait for serve() */ > + memcpy(saved, (void *)split, PAGE); > + if (madvise((void *)split, PAGE, MADV_DONTNEED)) > + _exit(1); > + } > + asm volatile(".irp i, " HANDLER_REGS "\n" > + "fld f\\i, \\i * 8(%[h])\n" > + ".endr\n" > + : : [h] "r" (handler_pattern) > + : "memory", "ft0", "ft1", "ft2", "ft3", "ft4", "ft5", > + "ft6", "ft7", "fa0", "fa1", "fa2", "fa3", "fa4", "fa5"); > +} > + > +static void *serve(void *arg) > +{ > + struct uffdio_copy copy = { .src = (unsigned long)saved, .len = PAGE }; > + struct uffd_msg msg; > + int fd = (long)arg; > + > + while (read(fd, &msg, sizeof(msg)) == sizeof(msg)) { > + copy.dst = msg.arg.pagefault.address & ~(PAGE - 1); > + copy.copy = 0; > + ioctl(fd, UFFDIO_COPY, ©); > + } > + return NULL; > +} > + > +TEST(fp_restore_frame_fault) > +{ > + struct sigaction sa = { > + .sa_sigaction = handler, > + .sa_flags = SA_SIGINFO | SA_ONSTACK, > + }; > + struct uffdio_api api = { .api = UFFD_API }; > + struct uffdio_register reg = { .mode = UFFDIO_REGISTER_MODE_MISSING }; > + stack_t ss = { .ss_size = STACK_SIZE }; > + long pid = getpid(), tid = syscall(__NR_gettid); > + uint64_t out[16]; > + unsigned long fcsr, shift; > + pthread_t thread; > + int fd, i; > + > + if (!(getauxval(AT_HWCAP) & COMPAT_HWCAP_ISA_D)) > + SKIP(return, "no D extension"); > + > + fd = syscall(__NR_userfaultfd, O_CLOEXEC); > + if (fd < 0) > + SKIP(return, "userfaultfd not available"); > + ASSERT_EQ(0, ioctl(fd, UFFDIO_API, &api)); > + > + for (i = 0; i < 16; i++) { > + pattern[i] = 0x4010000000000000ULL + i; > + handler_pattern[i] = 0xbff0000000000000ULL + i; > + } > + > + saved = mmap(NULL, PAGE, PROT_READ | PROT_WRITE, > + MAP_PRIVATE | MAP_ANONYMOUS, -1, 0); > + ASSERT_NE(MAP_FAILED, saved); > + ss.ss_sp = mmap(NULL, STACK_SIZE, PROT_READ | PROT_WRITE, > + MAP_PRIVATE | MAP_ANONYMOUS, -1, 0); > + ASSERT_NE(MAP_FAILED, ss.ss_sp); > + /* populate it, so only the page the handler drops faults */ > + memset(ss.ss_sp, 0, STACK_SIZE); > + reg.range.start = (unsigned long)ss.ss_sp; > + reg.range.len = STACK_SIZE; > + ASSERT_EQ(0, ioctl(fd, UFFDIO_REGISTER, ®)); > + ASSERT_EQ(0, pthread_create(&thread, NULL, serve, (void *)(long)fd)); > + ASSERT_EQ(0, sigaction(SIGUSR1, &sa, NULL)); > + > + /* lower the frame until the FP image crosses a page at SPLIT */ > + for (shift = 0; shift < PAGE && !placed; shift += 16) { > + register long a0 asm("a0") = pid; > + register long a1 asm("a1") = tid; > + register long a2 asm("a2") = SIGUSR1; > + register long a7 asm("a7") = __NR_tgkill; > + > + ss.ss_size = STACK_SIZE - shift; > + ASSERT_EQ(0, sigaltstack(&ss, NULL)); > + fcsr = 0x1f; > + asm volatile(".irp i, " F0_15 "\n" > + "fld f\\i, \\i * 8(%[in])\n" > + ".endr\n" > + "csrw fcsr, %[fcsr]\n" > + "ecall\n" > + "csrr %[fcsr], fcsr\n" > + ".irp i, " F0_15 "\n" > + "fsd f\\i, \\i * 8(%[out])\n" > + ".endr\n" > + : "+r" (a0), [fcsr] "+r" (fcsr) > + : "r" (a1), "r" (a2), "r" (a7), > + [in] "r" (pattern), [out] "r" (out) > + : "memory", "ft0", "ft1", "ft2", "ft3", "ft4", "ft5", > + "ft6", "ft7", "fs0", "fs1", "fa0", "fa1", "fa2", > + "fa3", "fa4", "fa5"); > + } > + ASSERT_TRUE(placed); > + > + for (i = 0; i < 16; i++) { > + EXPECT_EQ(pattern[i], out[i]) TH_LOG("f%d", i); > + } > + EXPECT_EQ(0x1fUL, fcsr); > +} > + > +TEST_HARNESS_MAIN > -- > 2.53.0 >