[PATCH -next v18 10/20] riscv: Allocate user's vector context in the first-use trap

Andy Chiu
2023-04-14T16:00:12Z

Vector unit is disabled by default for all user processes. Thus, a
process will take a trap (illegal instruction) into kernel at the first
time when it uses Vector. Only after then, the kernel allocates V
context and starts take care of the context for that user process.

Suggested-by: Richard Henderson <richard.henderson@linaro.org>
Link: https://lore.kernel.org/r/3923eeee-e4dc-0911-40bf-84c34aee962d@linaro.org
Signed-off-by: Andy Chiu <andy.chiu@sifive.com>
Acked-by: Heiko Stuebner <heiko.stuebner@vrull.eu>
Tested-by: Heiko Stuebner <heiko.stuebner@vrull.eu>
---

Changes in v18:
- Add blank lines (Heiko)
- Return immediately in insn_is_vector() if an insn matches (Heiko)

arch/riscv/include/asm/insn.h | 29 +++++++++++
arch/riscv/include/asm/vector.h | 2 +
arch/riscv/kernel/traps.c | 26 +++++++++-
arch/riscv/kernel/vector.c | 91 +++++++++++++++++++++++++++++++++
4 files changed, 146 insertions(+), 2 deletions(-)

diff --git a/arch/riscv/include/asm/insn.h b/arch/riscv/include/asm/insn.h
index 8d5c84f2d5ef..4e1505cef8aa 100644
--- a/arch/riscv/include/asm/insn.h
+++ b/arch/riscv/include/asm/insn.h
@@ -137,6 +137,26 @@
#define RVG_OPCODE_JALR 0x67
#define RVG_OPCODE_JAL 0x6f
#define RVG_OPCODE_SYSTEM 0x73
+#define RVG_SYSTEM_CSR_OFF 20
+#define RVG_SYSTEM_CSR_MASK GENMASK(12, 0)
+
+/* parts of opcode for RVF, RVD and RVQ */
+#define RVFDQ_FL_FS_WIDTH_OFF 12
+#define RVFDQ_FL_FS_WIDTH_MASK GENMASK(3, 0)
+#define RVFDQ_FL_FS_WIDTH_W 2
+#define RVFDQ_FL_FS_WIDTH_D 3
+#define RVFDQ_LS_FS_WIDTH_Q 4
+#define RVFDQ_OPCODE_FL 0x07
+#define RVFDQ_OPCODE_FS 0x27
+
+/* parts of opcode for RVV */
+#define RVV_OPCODE_VECTOR 0x57
+#define RVV_VL_VS_WIDTH_8 0
+#define RVV_VL_VS_WIDTH_16 5
+#define RVV_VL_VS_WIDTH_32 6
+#define RVV_VL_VS_WIDTH_64 7
+#define RVV_OPCODE_VL RVFDQ_OPCODE_FL
+#define RVV_OPCODE_VS RVFDQ_OPCODE_FS

/* parts of opcode for RVC*/
#define RVC_OPCODE_C0 0x0
@@ -304,6 +324,15 @@ static __always_inline bool riscv_insn_is_branch(u32 code)
(RVC_X(x_, RVC_B_IMM_7_6_OPOFF, RVC_B_IMM_7_6_MASK) << RVC_B_IMM_7_6_OFF) | \
(RVC_IMM_SIGN(x_) << RVC_B_IMM_SIGN_OFF); })

+#define RVG_EXTRACT_SYSTEM_CSR(x) \
+ ({typeof(x) x_ = (x); RV_X(x_, RVG_SYSTEM_CSR_OFF, RVG_SYSTEM_CSR_MASK); })
+
+#define RVFDQ_EXTRACT_FL_FS_WIDTH(x) \
+ ({typeof(x) x_ = (x); RV_X(x_, RVFDQ_FL_FS_WIDTH_OFF, \
+ RVFDQ_FL_FS_WIDTH_MASK); })
+
+#define RVV_EXRACT_VL_VS_WIDTH(x) RVFDQ_EXTRACT_FL_FS_WIDTH(x)
+
/*
* Get the immediate from a J-type instruction.
*
diff --git a/arch/riscv/include/asm/vector.h b/arch/riscv/include/asm/vector.h
index 121d700c6ada..a8881af83ce4 100644
--- a/arch/riscv/include/asm/vector.h
+++ b/arch/riscv/include/asm/vector.h
@@ -21,6 +21,7 @@

extern unsigned long riscv_v_vsize;
int riscv_v_setup_vsize(void);
+bool riscv_v_first_use_handler(struct pt_regs *regs);

static __always_inline bool has_vector(void)
{
@@ -165,6 +166,7 @@ struct pt_regs;

static inline int riscv_v_setup_vsize(void) { return -EOPNOTSUPP; }
static __always_inline bool has_vector(void) { return false; }
+static inline bool riscv_v_first_use_handler(struct pt_regs *regs) { return false; }
static inline bool riscv_v_vstate_query(struct pt_regs *regs) { return false; }
#define riscv_v_vsize (0)
#define riscv_v_vstate_save(task, regs) do {} while (0)
diff --git a/arch/riscv/kernel/traps.c b/arch/riscv/kernel/traps.c
index 8c258b78c925..24d309c6ab8d 100644
--- a/arch/riscv/kernel/traps.c
+++ b/arch/riscv/kernel/traps.c
@@ -26,6 +26,7 @@
#include <asm/ptrace.h>
#include <asm/syscall.h>
#include <asm/thread_info.h>
+#include <asm/vector.h>

int show_unhandled_signals = 1;

@@ -145,8 +146,29 @@ DO_ERROR_INFO(do_trap_insn_misaligned,
SIGBUS, BUS_ADRALN, "instruction address misaligned");
DO_ERROR_INFO(do_trap_insn_fault,
SIGSEGV, SEGV_ACCERR, "instruction access fault");
-DO_ERROR_INFO(do_trap_insn_illegal,
- SIGILL, ILL_ILLOPC, "illegal instruction");
+
+asmlinkage __visible __trap_section void do_trap_insn_illegal(struct pt_regs *regs)
+{
+ if (user_mode(regs)) {
+ irqentry_enter_from_user_mode(regs);
+
+ local_irq_enable();
+
+ if (!has_vector() || !riscv_v_first_use_handler(regs))
+ do_trap_error(regs, SIGILL, ILL_ILLOPC, regs->epc,
+ "Oops - illegal instruction");
+
+ irqentry_exit_to_user_mode(regs);
+ } else {
+ irqentry_state_t state = irqentry_nmi_enter(regs);
+
+ do_trap_error(regs, SIGILL, ILL_ILLOPC, regs->epc,
+ "Oops - illegal instruction");
+
+ irqentry_nmi_exit(regs, state);
+ }
+}
+
DO_ERROR_INFO(do_trap_load_fault,
SIGSEGV, SEGV_ACCERR, "load access fault");
#ifndef CONFIG_RISCV_M_MODE
diff --git a/arch/riscv/kernel/vector.c b/arch/riscv/kernel/vector.c
index 53bb32546248..1457dc6f6fd4 100644
--- a/arch/riscv/kernel/vector.c
+++ b/arch/riscv/kernel/vector.c
@@ -4,10 +4,19 @@
* Author: Andy Chiu <andy.chiu@sifive.com>
*/
#include <linux/export.h>
+#include <linux/sched/signal.h>
+#include <linux/types.h>
+#include <linux/slab.h>
+#include <linux/sched.h>
+#include <linux/uaccess.h>

+#include <asm/thread_info.h>
+#include <asm/processor.h>
+#include <asm/insn.h>
#include <asm/vector.h>
#include <asm/csr.h>
#include <asm/elf.h>
+#include <asm/ptrace.h>
#include <asm/bug.h>

unsigned long riscv_v_vsize __read_mostly;
@@ -34,3 +43,85 @@ int riscv_v_setup_vsize(void)

return 0;
}
+
+static bool insn_is_vector(u32 insn_buf)
+{
+ u32 opcode = insn_buf & __INSN_OPCODE_MASK;
+ u32 width, csr;
+
+ /*
+ * All V-related instructions, including CSR operations are 4-Byte. So,
+ * do not handle if the instruction length is not 4-Byte.
+ */
+ if (unlikely(GET_INSN_LENGTH(insn_buf) != 4))
+ return false;
+
+ switch (opcode) {
+ case RVV_OPCODE_VECTOR:
+ return true;
+ case RVV_OPCODE_VL:
+ case RVV_OPCODE_VS:
+ width = RVV_EXRACT_VL_VS_WIDTH(insn_buf);
+ if (width == RVV_VL_VS_WIDTH_8 || width == RVV_VL_VS_WIDTH_16 ||
+ width == RVV_VL_VS_WIDTH_32 || width == RVV_VL_VS_WIDTH_64)
+ return true;
+
+ break;
+ case RVG_OPCODE_SYSTEM:
+ csr = RVG_EXTRACT_SYSTEM_CSR(insn_buf);
+ if ((csr >= CSR_VSTART && csr <= CSR_VCSR) ||
+ (csr >= CSR_VL && csr <= CSR_VLENB))
+ return true;
+ }
+
+ return false;
+}
+
+static int riscv_v_thread_zalloc(void)
+{
+ void *datap;
+
+ datap = kzalloc(riscv_v_vsize, GFP_KERNEL);
+ if (!datap)
+ return -ENOMEM;
+
+ current->thread.vstate.datap = datap;
+ memset(&current->thread.vstate, 0, offsetof(struct __riscv_v_ext_state,
+ datap));
+ return 0;
+}
+
+bool riscv_v_first_use_handler(struct pt_regs *regs)
+{
+ u32 __user *epc = (u32 __user *)regs->epc;
+ u32 insn = (u32)regs->badaddr;
+
+ /* If V has been enabled then it is not the first-use trap */
+ if (riscv_v_vstate_query(regs))
+ return false;
+
+ /* Get the instruction */
+ if (!insn) {
+ if (__get_user(insn, epc))
+ return false;
+ }
+
+ /* Filter out non-V instructions */
+ if (!insn_is_vector(insn))
+ return false;
+
+ /* Sanity check. datap should be null by the time of the first-use trap */
+ WARN_ON(current->thread.vstate.datap);
+
+ /*
+ * Now we sure that this is a V instruction. And it executes in the
+ * context where VS has been off. So, try to allocate the user's V
+ * context and resume execution.
+ */
+ if (riscv_v_thread_zalloc()) {
+ force_sig(SIGKILL);
+ return true;
+ }
+ riscv_v_vstate_on(regs);
+ return true;
+}
--
2.17.1