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Message-ID: <ef02ff0d-10b0-47db-93dc-3cb9f6db140e@rivosinc.com>
Date: Mon, 9 Oct 2023 15:02:52 +0200
From: Clément Léger <cleger@...osinc.com>
To: Björn Töpel <bjorn@...nel.org>,
Paul Walmsley <paul.walmsley@...ive.com>,
Palmer Dabbelt <palmer@...belt.com>,
Albert Ou <aou@...s.berkeley.edu>
Cc: Atish Patra <atishp@...osinc.com>,
Andrew Jones <ajones@...tanamicro.com>,
Evan Green <evan@...osinc.com>,
Björn Topel <bjorn@...osinc.com>,
linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org,
Ron Minnich <rminnich@...il.com>,
Daniel Maslowski <cyrevolt@...glemail.com>,
Conor Dooley <conor@...nel.org>
Subject: Re: [PATCH v2 2/8] riscv: add support for misaligned trap handling in
S-mode
On 04/10/2023 19:00, Björn Töpel wrote:
> Clément Léger <cleger@...osinc.com> writes:
>
>> Misalignment trap handling is only supported for M-mode and uses direct
>> accesses to user memory. In S-mode, when handling usermode fault, this
>> requires to use the get_user()/put_user() accessors. Implement
>> load_u8(), store_u8() and get_insn() using these accessors for
>> userspace and direct text access for kernel.
>>
>> Signed-off-by: Clément Léger <cleger@...osinc.com>
>> ---
>> arch/riscv/Kconfig | 8 ++
>> arch/riscv/include/asm/entry-common.h | 14 +++
>> arch/riscv/kernel/Makefile | 2 +-
>> arch/riscv/kernel/traps.c | 9 --
>> arch/riscv/kernel/traps_misaligned.c | 119 +++++++++++++++++++++++---
>> 5 files changed, 129 insertions(+), 23 deletions(-)
>>
>> diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
>> index d607ab0f7c6d..6e167358a897 100644
>> --- a/arch/riscv/Kconfig
>> +++ b/arch/riscv/Kconfig
>> @@ -636,6 +636,14 @@ config THREAD_SIZE_ORDER
>> Specify the Pages of thread stack size (from 4KB to 64KB), which also
>> affects irq stack size, which is equal to thread stack size.
>>
>> +config RISCV_MISALIGNED
>> + bool "Support misaligned load/store traps for kernel and userspace"
>> + default y
>> + help
>> + Say Y here if you want the kernel to embed support for misaligned
>> + load/store for both kernel and userspace. When disable, misaligned
>> + accesses will generate SIGBUS in userspace and panic in kernel.
>> +
>> endmenu # "Platform type"
>>
>> menu "Kernel features"
>> diff --git a/arch/riscv/include/asm/entry-common.h b/arch/riscv/include/asm/entry-common.h
>> index 6e4dee49d84b..7ab5e34318c8 100644
>> --- a/arch/riscv/include/asm/entry-common.h
>> +++ b/arch/riscv/include/asm/entry-common.h
>> @@ -8,4 +8,18 @@
>> void handle_page_fault(struct pt_regs *regs);
>> void handle_break(struct pt_regs *regs);
>>
>> +#ifdef CONFIG_RISCV_MISALIGNED
>> +int handle_misaligned_load(struct pt_regs *regs);
>> +int handle_misaligned_store(struct pt_regs *regs);
>> +#else
>> +static inline int handle_misaligned_load(struct pt_regs *regs)
>> +{
>> + return -1;
>> +}
>> +static inline int handle_misaligned_store(struct pt_regs *regs)
>> +{
>> + return -1;
>> +}
>> +#endif
>> +
>> #endif /* _ASM_RISCV_ENTRY_COMMON_H */
>> diff --git a/arch/riscv/kernel/Makefile b/arch/riscv/kernel/Makefile
>> index 95cf25d48405..0d874fb24b51 100644
>> --- a/arch/riscv/kernel/Makefile
>> +++ b/arch/riscv/kernel/Makefile
>> @@ -59,7 +59,7 @@ obj-y += patch.o
>> obj-y += probes/
>> obj-$(CONFIG_MMU) += vdso.o vdso/
>>
>> -obj-$(CONFIG_RISCV_M_MODE) += traps_misaligned.o
>> +obj-$(CONFIG_RISCV_MISALIGNED) += traps_misaligned.o
>> obj-$(CONFIG_FPU) += fpu.o
>> obj-$(CONFIG_RISCV_ISA_V) += vector.o
>> obj-$(CONFIG_SMP) += smpboot.o
>> diff --git a/arch/riscv/kernel/traps.c b/arch/riscv/kernel/traps.c
>> index 19807c4d3805..d69779e4b967 100644
>> --- a/arch/riscv/kernel/traps.c
>> +++ b/arch/riscv/kernel/traps.c
>> @@ -179,14 +179,6 @@ asmlinkage __visible __trap_section void do_trap_insn_illegal(struct pt_regs *re
>>
>> DO_ERROR_INFO(do_trap_load_fault,
>> SIGSEGV, SEGV_ACCERR, "load access fault");
>> -#ifndef CONFIG_RISCV_M_MODE
>> -DO_ERROR_INFO(do_trap_load_misaligned,
>> - SIGBUS, BUS_ADRALN, "Oops - load address misaligned");
>> -DO_ERROR_INFO(do_trap_store_misaligned,
>> - SIGBUS, BUS_ADRALN, "Oops - store (or AMO) address misaligned");
>> -#else
>> -int handle_misaligned_load(struct pt_regs *regs);
>> -int handle_misaligned_store(struct pt_regs *regs);
>>
>> asmlinkage __visible __trap_section void do_trap_load_misaligned(struct pt_regs *regs)
>> {
>> @@ -229,7 +221,6 @@ asmlinkage __visible __trap_section void do_trap_store_misaligned(struct pt_regs
>> irqentry_nmi_exit(regs, state);
>> }
>> }
>> -#endif
>> DO_ERROR_INFO(do_trap_store_fault,
>> SIGSEGV, SEGV_ACCERR, "store (or AMO) access fault");
>> DO_ERROR_INFO(do_trap_ecall_s,
>> diff --git a/arch/riscv/kernel/traps_misaligned.c b/arch/riscv/kernel/traps_misaligned.c
>> index e7bfb33089c1..9daed7d756ae 100644
>> --- a/arch/riscv/kernel/traps_misaligned.c
>> +++ b/arch/riscv/kernel/traps_misaligned.c
>> @@ -12,6 +12,7 @@
>> #include <asm/processor.h>
>> #include <asm/ptrace.h>
>> #include <asm/csr.h>
>> +#include <asm/entry-common.h>
>>
>> #define INSN_MATCH_LB 0x3
>> #define INSN_MASK_LB 0x707f
>> @@ -151,21 +152,25 @@
>> #define PRECISION_S 0
>> #define PRECISION_D 1
>>
>> -static inline u8 load_u8(const u8 *addr)
>> +#ifdef CONFIG_RISCV_M_MODE
>> +static inline int load_u8(struct pt_regs *regs, const u8 *addr, u8 *r_val)
>> {
>> u8 val;
>>
>> asm volatile("lbu %0, %1" : "=&r" (val) : "m" (*addr));
>> + *r_val = val;
>>
>> - return val;
>> + return 0;
>> }
>>
>> -static inline void store_u8(u8 *addr, u8 val)
>> +static inline int store_u8(struct pt_regs *regs, u8 *addr, u8 val)
>> {
>> asm volatile ("sb %0, %1\n" : : "r" (val), "m" (*addr));
>> +
>> + return 0;
>> }
>>
>> -static inline ulong get_insn(ulong mepc)
>> +static inline int get_insn(struct pt_regs *regs, ulong mepc, ulong *r_insn)
>> {
>> register ulong __mepc asm ("a2") = mepc;
>> ulong val, rvc_mask = 3, tmp;
>> @@ -194,9 +199,87 @@ static inline ulong get_insn(ulong mepc)
>> : [addr] "r" (__mepc), [rvc_mask] "r" (rvc_mask),
>> [xlen_minus_16] "i" (XLEN_MINUS_16));
>>
>> - return val;
>> + *r_insn = val;
>> +
>> + return 0;
>> +}
>> +#else
>> +static inline int load_u8(struct pt_regs *regs, const u8 *addr, u8 *r_val)
>> +{
>> + if (user_mode(regs)) {
>> + return __get_user(*r_val, addr);
>> + } else {
>> + *r_val = *addr;
>> + return 0;
>> + }
>
> One nit (...well two) ;-)
>
> If you're respinning I'd get rid of the "inlines",and personally I
> think early exit is easier to read. Applies to the whole patch.
Noted, I'll fix that (checkpatch suggested it so that makes sense).
Clément
>
> | {
> | if (user_mode(regs))
> | return __get_user(*r_val, addr);
> |
> | *r_val = *addr;
> | return 0;
> | }
>
>
> Regardless if you change or not,
>
> Reviewed-by: Björn Töpel <bjorn@...osinc.com>
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