On Thu, 18 May 2023 09:19:34 PDT (-0700), andy.chiu@xxxxxxxxxx wrote:
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@xxxxxxxxxx> Link: https://lore.kernel.org/r/3923eeee-e4dc-0911-40bf-84c34aee962d@xxxxxxxxxx Signed-off-by: Andy Chiu <andy.chiu@xxxxxxxxxx> --- Hey Heiko and Conor, I am dropping you guys' A-b, T-b, and R-b because I added a check in riscv_v_first_use_handler(). Changelog v20: - move has_vector() into vector.c for better code readibility - check elf_hwcap in the first-use trap because it might get turned off if cores have different VLENs. Changelog 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 | 95 +++++++++++++++++++++++++++++++++ 4 files changed, 150 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 ce6a75e9cf62..8e56da67b5cf 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..05ffdcd1424e 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 (!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 120f1ce9abf9..0080798e8d2e 100644 --- a/arch/riscv/kernel/vector.c +++ b/arch/riscv/kernel/vector.c @@ -4,10 +4,19 @@ * Author: Andy Chiu <andy.chiu@xxxxxxxxxx> */ #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 +43,89 @@ 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(¤t->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; + + /* Do not handle if V is not supported, or disabled */ + if (!has_vector() || !(elf_hwcap & COMPAT_HWCAP_ISA_V)) + return false; + + /* 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);
Is SIGKILL too strong? Maybe we just SIGILL here? Maybe killing the process is the right way to go, though: if we're that out of memory something's getting killed, it might as well be whatever's about to get confused by vectors disappearing.
+ return true; + } + riscv_v_vstate_on(regs); + return true; +}
Reviewed-by: Palmer Dabbelt <palmer@xxxxxxxxxxxx>
