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 [5].
Ssdbltrp can be tested using qemu[2], opensbi (master branch), linux[3] and
kvm-unit-tests[4]. 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 -C dbltrp_v6 dev/cleger/dbltrp_v6
$ mkdir build && cd build
$ ../configure --target-list=riscv64-softmmu
$ make
OpenSBI:
$ git clone https://github.com/rivosinc/opensbi.git
$ cd opensbi
$ make O=build PLATFORM_RISCV_XLEN=64 PLATFORM=generic
Linux:
$ git clone https://github.com/rivosinc/linux.git
$ cd linux
$ git switch -C dbltrp_v1 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 -C dbltrp_v1 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_v5 [2]
Link: https://github.com/rivosinc/linux/tree/dev/cleger/dbltrp_v1 [3]
Link: https://github.com/clementleger/kvm-unit-tests/tree/dev/cleger/dbltrp_v1 [4]
Link: https://lore.kernel.org/qemu-riscv/20241122032217.3816540-1-frank.chang@sifive.com/T/ [5]
---
V6:
- Simplify and fix write_henvcfg() masking by assigning the written
value to henvcfg and mask the value to be written as well as clearing
the upper part of henvcfgh upon writing.
- Rebased on RNMI v9 series.
V5:
- Use 0 instead of false to set MSTATUS_MDT in helper_mnret()
- Added explicit comments about henvcfg write mask being tricky.
- Fixed a invalid menvcfg_mask in write_henvcfgh
V4:
- Remove DTE from sstatus_v1_10_mask variable and add specific if for
DTE masking where it's used.
- Use mstatus_hs.sdt field rather than setting DTE to 0 in
riscv_do_cpu_interrupt().
- Add a fix for henvcfg value which was incorrectly set after changing
menvcfg
- Remove useless ext_ssdbltrp check in
riscv_env_smode_dbltrp_enabled().
- Remove useless mstatus clear in write_mstatus().
- Add proper handling of SDT writing to vsstatus.
- Add clearing of vsstatus//mstatus SDT field when DTE is disabled.
- Fix wrong value being written for MDT/MIE in write_mstatush().
- Rebased on Frank Snrnmi v7
V3:
- Fix spec version from 1.12 to 1.13 for Smdbltrp and Ssdbltrp
- Add better comments for dte/sdt computation in
riscv_cpu_do_interrupt().
- Move some CSR related changes to the CSRs related commits.
V2:
- Squashed commits that added ext_s{s|m}dbltrp as suggested by Daniel
Clément Léger (9):
target/riscv: fix henvcfg potentially containing stale bits
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 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 | 115 +++++++++++++++++++++++++++++++-------
target/riscv/csr.c | 95 ++++++++++++++++++++++++++-----
target/riscv/op_helper.c | 47 +++++++++++++++-
7 files changed, 239 insertions(+), 38 deletions(-)
--
2.45.2