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Subject[PATCH v2 22/31] arm64: Floating point and SIMD
Date
This patch adds support for FP/ASIMD register bank saving and restoring
during context switch and FP exception handling to generate SIGFPE.
There are 32 128-bit registers and the context switching is currently
done non-lazily. Benchmarks on real hardware are required before
implementing lazy FP state saving/restoring.

Signed-off-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
---
arch/arm64/include/asm/fpsimd.h | 64 +++++++++++++++++++++++
arch/arm64/kernel/entry-fpsimd.S | 80 ++++++++++++++++++++++++++++
arch/arm64/kernel/fpsimd.c | 106 ++++++++++++++++++++++++++++++++++++++
3 files changed, 250 insertions(+), 0 deletions(-)
create mode 100644 arch/arm64/include/asm/fpsimd.h
create mode 100644 arch/arm64/kernel/entry-fpsimd.S
create mode 100644 arch/arm64/kernel/fpsimd.c

diff --git a/arch/arm64/include/asm/fpsimd.h b/arch/arm64/include/asm/fpsimd.h
new file mode 100644
index 0000000..7ea4711
--- /dev/null
+++ b/arch/arm64/include/asm/fpsimd.h
@@ -0,0 +1,64 @@
+/*
+ * Copyright (C) 2012 ARM Ltd.
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program. If not, see <http://www.gnu.org/licenses/>.
+ */
+#ifndef __ASM_FP_H
+#define __ASM_FP_H
+
+#include <asm/ptrace.h>
+
+#ifndef __ASSEMBLY__
+
+/*
+ * FP/SIMD storage area has:
+ * - FPSR and FPCR
+ * - 32 128-bit data registers
+ *
+ * Note that user_fp forms a prefix of this structure, which is relied
+ * upon in the ptrace FP/SIMD accessors. struct user_fpsimd_state must
+ * form a prefix of struct fpsimd_state.
+ */
+struct fpsimd_state {
+ union {
+ struct user_fpsimd_state user_fpsimd;
+ struct {
+ __uint128_t vregs[32];
+ u32 fpsr;
+ u32 fpcr;
+ };
+ };
+};
+
+#if defined(__KERNEL__) && defined(CONFIG_AARCH32_EMULATION)
+/* Masks for extracting the FPSR and FPCR from the FPSCR */
+#define VFP_FPSCR_STAT_MASK 0xf800009f
+#define VFP_FPSCR_CTRL_MASK 0x07f79f00
+/*
+ * The VFP state has 32x64-bit registers and a single 32-bit
+ * control/status register.
+ */
+#define VFP_STATE_SIZE ((32 * 8) + 4)
+#endif
+
+struct task_struct;
+
+extern void fpsimd_save_state(struct fpsimd_state *state);
+extern void fpsimd_load_state(struct fpsimd_state *state);
+
+extern void fpsimd_thread_switch(struct task_struct *next);
+extern void fpsimd_flush_thread(void);
+
+#endif
+
+#endif
diff --git a/arch/arm64/kernel/entry-fpsimd.S b/arch/arm64/kernel/entry-fpsimd.S
new file mode 100644
index 0000000..17988a6
--- /dev/null
+++ b/arch/arm64/kernel/entry-fpsimd.S
@@ -0,0 +1,80 @@
+/*
+ * FP/SIMD state saving and restoring
+ *
+ * Copyright (C) 2012 ARM Ltd.
+ * Author: Catalin Marinas <catalin.marinas@arm.com>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include <linux/linkage.h>
+
+#include <asm/assembler.h>
+
+/*
+ * Save the FP registers.
+ *
+ * x0 - pointer to struct fpsimd_state
+ */
+ENTRY(fpsimd_save_state)
+ stp q0, q1, [x0, #16 * 0]
+ stp q2, q3, [x0, #16 * 2]
+ stp q4, q5, [x0, #16 * 4]
+ stp q6, q7, [x0, #16 * 6]
+ stp q8, q9, [x0, #16 * 8]
+ stp q10, q11, [x0, #16 * 10]
+ stp q12, q13, [x0, #16 * 12]
+ stp q14, q15, [x0, #16 * 14]
+ stp q16, q17, [x0, #16 * 16]
+ stp q18, q19, [x0, #16 * 18]
+ stp q20, q21, [x0, #16 * 20]
+ stp q22, q23, [x0, #16 * 22]
+ stp q24, q25, [x0, #16 * 24]
+ stp q26, q27, [x0, #16 * 26]
+ stp q28, q29, [x0, #16 * 28]
+ stp q30, q31, [x0, #16 * 30]!
+ mrs x8, fpsr
+ str w8, [x0, #16 * 2]
+ mrs x8, fpcr
+ str w8, [x0, #16 * 2 + 4]
+ ret
+ENDPROC(fpsimd_save_state)
+
+/*
+ * Load the FP registers.
+ *
+ * x0 - pointer to struct fpsimd_state
+ */
+ENTRY(fpsimd_load_state)
+ ldp q0, q1, [x0, #16 * 0]
+ ldp q2, q3, [x0, #16 * 2]
+ ldp q4, q5, [x0, #16 * 4]
+ ldp q6, q7, [x0, #16 * 6]
+ ldp q8, q9, [x0, #16 * 8]
+ ldp q10, q11, [x0, #16 * 10]
+ ldp q12, q13, [x0, #16 * 12]
+ ldp q14, q15, [x0, #16 * 14]
+ ldp q16, q17, [x0, #16 * 16]
+ ldp q18, q19, [x0, #16 * 18]
+ ldp q20, q21, [x0, #16 * 20]
+ ldp q22, q23, [x0, #16 * 22]
+ ldp q24, q25, [x0, #16 * 24]
+ ldp q26, q27, [x0, #16 * 26]
+ ldp q28, q29, [x0, #16 * 28]
+ ldp q30, q31, [x0, #16 * 30]!
+ ldr w8, [x0, #16 * 2]
+ ldr w9, [x0, #16 * 2 + 4]
+ msr fpsr, x8
+ msr fpcr, x9
+ ret
+ENDPROC(fpsimd_load_state)
diff --git a/arch/arm64/kernel/fpsimd.c b/arch/arm64/kernel/fpsimd.c
new file mode 100644
index 0000000..e8b8357
--- /dev/null
+++ b/arch/arm64/kernel/fpsimd.c
@@ -0,0 +1,106 @@
+/*
+ * FP/SIMD context switching and fault handling
+ *
+ * Copyright (C) 2012 ARM Ltd.
+ * Author: Catalin Marinas <catalin.marinas@arm.com>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include <linux/kernel.h>
+#include <linux/init.h>
+#include <linux/sched.h>
+#include <linux/signal.h>
+
+#include <asm/fpsimd.h>
+#include <asm/cputype.h>
+
+#define FPEXC_IOF (1 << 0)
+#define FPEXC_DZF (1 << 1)
+#define FPEXC_OFF (1 << 2)
+#define FPEXC_UFF (1 << 3)
+#define FPEXC_IXF (1 << 4)
+#define FPEXC_IDF (1 << 7)
+
+/*
+ * Trapped FP/ASIMD access.
+ */
+void do_fpsimd_acc(unsigned int esr, struct pt_regs *regs)
+{
+ /* TODO: implement lazy context saving/restoring */
+ WARN_ON(1);
+}
+
+/*
+ * Raise a SIGFPE for the current process.
+ */
+void do_fpsimd_exc(unsigned int esr, struct pt_regs *regs)
+{
+ siginfo_t info;
+ unsigned int si_code = 0;
+
+ if (esr & FPEXC_IOF)
+ si_code = FPE_FLTINV;
+ else if (esr & FPEXC_DZF)
+ si_code = FPE_FLTDIV;
+ else if (esr & FPEXC_OFF)
+ si_code = FPE_FLTOVF;
+ else if (esr & FPEXC_UFF)
+ si_code = FPE_FLTUND;
+ else if (esr & FPEXC_IXF)
+ si_code = FPE_FLTRES;
+
+ memset(&info, 0, sizeof(info));
+ info.si_signo = SIGFPE;
+ info.si_code = si_code;
+ info.si_addr = (void __user *)instruction_pointer(regs);
+
+ send_sig_info(SIGFPE, &info, current);
+}
+
+void fpsimd_thread_switch(struct task_struct *next)
+{
+ /* check if not kernel threads */
+ if (current->mm)
+ fpsimd_save_state(&current->thread.fpsimd_state);
+ if (next->mm)
+ fpsimd_load_state(&next->thread.fpsimd_state);
+}
+
+void fpsimd_flush_thread(void)
+{
+ memset(&current->thread.fpsimd_state, 0, sizeof(struct fpsimd_state));
+ fpsimd_load_state(&current->thread.fpsimd_state);
+}
+
+/*
+ * FP/SIMD support code initialisation.
+ */
+static int __init fpsimd_init(void)
+{
+ u64 pfr = read_cpuid(ID_AA64PFR0_EL1);
+
+ if (pfr & (0xf << 16)) {
+ pr_notice("Floating-point is not implemented\n");
+ return 0;
+ }
+ elf_hwcap |= HWCAP_FP;
+
+ if (pfr & (0xf << 20))
+ pr_notice("Advanced SIMD is not implemented\n");
+ else
+ elf_hwcap |= HWCAP_ASIMD;
+
+ return 0;
+}
+late_initcall(fpsimd_init);


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