A double trap typically arises during a sensitive phase in trap handling operations — when an exception or interrupt occurs while the trap handler (the component responsible for managing these events) is in a non-reentrant state. This non-reentrancy usually occurs in the early phase of trap handling, wherein the trap handler has not yet preserved the necessary state to handle and resume from the trap. The occurrence of such event is unlikely but can happen when dealing with hardware errors.
This series adds support for Ssdbltrp and Smdbltrp ratified ISA extensions [1]. It is based on the Smrnmi series [6]. Ssdbltrp can be tested using qemu[2], opensbi[3], linux[4] and kvm-unit-tests[5]. Assuming you have a riscv environment available and configured (CROSS_COMPILE), it can be built for riscv64 using the following instructions: Qemu: $ git clone https://github.com/rivosinc/qemu.git $ cd qemu $ git switch dev/cleger/dbltrp_v1 $ mkdir build && cd build $ ../configure --target-list=riscv64-softmmu $ make OpenSBI: $ git clone https://github.com/rivosinc/opensbi.git $ cd opensbi $ git switch dev/cleger/dbltrp_v1 $ make O=build PLATFORM_RISCV_XLEN=64 PLATFORM=generic Linux: $ git clone https://github.com/rivosinc/linux.git $ cd linux $ git switch dev/cleger/dbltrp_v1 $ export ARCH=riscv $ make O=build defconfig $ ./script/config --file build/.config --enable RISCV_DBLTRP $ make O=build kvm-unit-tests: $ git clone https://github.com/clementleger/kvm-unit-tests.git $ cd kvm-unit-tests $ git switch dev/cleger/dbltrp_v1 $ ./configure --arch=riscv64 --cross-prefix=$CROSS_COMPILE $ make You will also need kvmtool in your rootfs. Run with kvm-unit-test test as kernel: $ qemu-system-riscv64 \ -M virt \ -cpu rv64,ssdbltrp=true,smdbltrp=true \ -nographic \ -serial mon:stdio \ -bios opensbi/build/platform/generic/firmware/fw_jump.bin \ -kernel kvm-unit-tests-dbltrp/riscv/sbi_dbltrp.flat ... [OpenSBI boot partially elided] Boot HART ISA Extensions : sscofpmf,sstc,zicntr,zihpm,zicboz,zicbom,sdtrig,svadu,ssdbltrp ... ########################################################################## # kvm-unit-tests ########################################################################## PASS: sbi: fwft: FWFT extension probing no error PASS: sbi: fwft: FWFT extension is present PASS: sbi: fwft: dbltrp: Get double trap enable feature value PASS: sbi: fwft: dbltrp: Set double trap enable feature value == 0 PASS: sbi: fwft: dbltrp: Get double trap enable feature value == 0 PASS: sbi: fwft: dbltrp: Double trap disabled, trap first time ok PASS: sbi: fwft: dbltrp: Set double trap enable feature value == 1 PASS: sbi: fwft: dbltrp: Get double trap enable feature value == 1 PASS: sbi: fwft: dbltrp: Trapped twice allowed ok INFO: sbi: fwft: dbltrp: Should generate a double trap and crash ! sbi_trap_error: hart0: trap0: double trap handler failed (error -10) sbi_trap_error: hart0: trap0: mcause=0x0000000000000010 mtval=0x0000000000000000 sbi_trap_error: hart0: trap0: mtval2=0x0000000000000003 mtinst=0x0000000000000000 sbi_trap_error: hart0: trap0: mepc=0x00000000802000d8 mstatus=0x8000000a01006900 sbi_trap_error: hart0: trap0: ra=0x00000000802001fc sp=0x0000000080213e70 sbi_trap_error: hart0: trap0: gp=0x0000000000000000 tp=0x0000000080088000 sbi_trap_error: hart0: trap0: s0=0x0000000080213e80 s1=0x0000000000000001 sbi_trap_error: hart0: trap0: a0=0x0000000080213e80 a1=0x0000000080208193 sbi_trap_error: hart0: trap0: a2=0x000000008020dc20 a3=0x000000000000000f sbi_trap_error: hart0: trap0: a4=0x0000000080210cd8 a5=0x00000000802110d0 sbi_trap_error: hart0: trap0: a6=0x00000000802136e4 a7=0x0000000046574654 sbi_trap_error: hart0: trap0: s2=0x0000000080210cd9 s3=0x0000000000000000 sbi_trap_error: hart0: trap0: s4=0x0000000000000000 s5=0x0000000000000000 sbi_trap_error: hart0: trap0: s6=0x0000000000000000 s7=0x0000000000000001 sbi_trap_error: hart0: trap0: s8=0x0000000000002000 s9=0x0000000080083700 sbi_trap_error: hart0: trap0: s10=0x0000000000000000 s11=0x0000000000000000 sbi_trap_error: hart0: trap0: t0=0x0000000000000000 t1=0x0000000080213ed8 sbi_trap_error: hart0: trap0: t2=0x0000000000001000 t3=0x0000000080213ee0 sbi_trap_error: hart0: trap0: t4=0x0000000000000000 t5=0x000000008020f8d0 sbi_trap_error: hart0: trap0: t6=0x0000000000000000 Run with linux and kvm-unit-test test in kvm (testing VS-mode): $ qemu-system-riscv64 \ -M virt \ -cpu rv64,ssdbltrp=true,smdbltrp=true \ -nographic \ -serial mon:stdio \ -bios opensbi/build/platform/generic/firmware/fw_jump.bin \ -kernel linux/build/arch/riscv/boot/Image ... [Linux boot partially elided] [ 0.735079] riscv-dbltrp: Double trap handling registered ... $ lkvm run -k sbi_dbltrp.flat -m 128 -c 2 ########################################################################## # kvm-unit-tests ########################################################################## PASS: sbi: fwft: FWFT extension probing no error PASS: sbi: fwft: FWFT extension is present PASS: sbi: fwft: dbltrp: Get double trap enable feature value PASS: sbi: fwft: dbltrp: Set double trap enable feature value == 0 PASS: sbi: fwft: dbltrp: Get double trap enable feature value == 0 PASS: sbi: fwft: dbltrp: Double trap disabled, trap first time ok PASS: sbi: fwft: dbltrp: Set double trap enable feature value == 1 PASS: sbi: fwft: dbltrp: Get double trap enable feature value == 1 PASS: sbi: fwft: dbltrp: Trapped twice allowed ok INFO: sbi: fwft: dbltrp: Should generate a double trap and crash ! [ 51.939077] Guest double trap [ 51.939323] kvm [93]: VCPU exit error -95 [ 51.939683] kvm [93]: SEPC=0x802000d8 SSTATUS=0x200004520 HSTATUS=0x200200180 [ 51.939947] kvm [93]: SCAUSE=0x10 STVAL=0x0 HTVAL=0x3 HTINST=0x0 KVM_RUN failed: Operation not supported $ Testing Smbdbltrp can be done using gdb and trigger some trap. For instance, interrupt M-mode firmware at some point, set mstatus.mdt = 1 and corrupt some register to generate a NULL pointer exception. Link: https://github.com/riscv/riscv-isa-manual/commit/52a5742d5ab5a0792019033631b2035a493ad981 [1] Link: https://github.com/rivosinc/qemu/tree/dev/cleger/dbltrp_v1 [2] Link: https://github.com/rivosinc/opensbi/tree/dev/cleger/dbltrp_v1 [3] Link: https://github.com/rivosinc/linux/tree/dev/cleger/dbltrp_v1 [4] Link: https://github.com/clementleger/kvm-unit-tests/tree/dev/cleger/dbltrp_v1 [5] Link: https://lore.kernel.org/all/CAKmqyKO9k93OLX_pxtkHcUAvC=nunxtp6mdcb2j2zwhmnfb...@mail.gmail.com/T/ [6] --- Clément Léger (10): target/riscv: Add `ext_ssdbltrp` in RISCVCPUConfig. target/riscv: Add Ssdbltrp CSRs handling target/riscv: Implement Ssdbltrp sret, mret and mnret behavior target/riscv: Implement Ssdbltrp exception handling target/riscv: Add Ssdbltrp ISA extension enable switch target/riscv: Add `ext_smdbltrp` in RISCVCPUConfig. target/riscv: Add Smdbltrp CSRs handling target/riscv: Implement Smdbltrp sret, mret and mnret behavior target/riscv: Implement Smdbltrp behavior target/riscv: Add Smdbltrp ISA extension enable switch target/riscv/cpu.c | 9 +++- target/riscv/cpu.h | 1 + target/riscv/cpu_bits.h | 8 ++++ target/riscv/cpu_cfg.h | 2 + target/riscv/cpu_helper.c | 98 +++++++++++++++++++++++++++++++++------ target/riscv/csr.c | 60 ++++++++++++++++++++---- target/riscv/op_helper.c | 47 ++++++++++++++++++- 7 files changed, 198 insertions(+), 27 deletions(-) -- 2.45.2
