Re: [PATCH v4] riscv: Use Zalrsc extension to implement atomic functions

From: Jesse Taube

Date: Mon Jul 27 2026 - 18:38:36 EST

On Mon, Jul 27, 2026 at 5:03 PM Jesse Taube <jtaubepe@xxxxxxxxxx> wrote:
>
> On Thu, Jul 23, 2026 at 11:53 AM Aleksa Paunovic via B4 Relay
> <devnull+aleksa.paunovic.htecgroup.com@xxxxxxxxxx> wrote:
> >
> > From: Chao-ying Fu <cfu@xxxxxxxx>
> >
> > MIPS P8700 does not natively support Zaamo instructions.
> > They are emulated with Zalrsc extension instructions instead [1].
> > Since the emulation is implemented through M-mode traps in the SBI
> > layer, it is best to avoid using these instructions wherever possible on
> > the P8700.
> >
> > Implement kernel atomic operations using LR/SC sequences only.
> > This is achieved by using the errata mechanism, with minimal
> > interference on other cores.
> >
> > Signed-off-by: Chao-ying Fu <cfu@xxxxxxxx>
> > Signed-off-by: Aleksandar Rikalo <arikalo@xxxxxxxxx>
> > Co-developed-by: Aleksa Paunovic <aleksa.paunovic@xxxxxxxxxxxxx>
> > Signed-off-by: Aleksa Paunovic <aleksa.paunovic@xxxxxxxxxxxxx>

Tested-by: Jesse Taube <jtaubepe@xxxxxxxxxx>

> >
> > [1] https://mips.com/wp-content/uploads/2026/03/MIPS_P8700_P8700-F_Programmers_Reference_Guide_Rev1.86_2-17-2026.pdf
> >
> > ---
> > The patch was tested on QEMU configured to emulate an eight-hart MIPS P8700 CPU.
>
> Can you share the tests. I made my own tests a while back here:
> https://github.com/Mr-Bossman/zalrsc-buildroot/tree/master
> Though they don't seem to boot without the zaamo extension

I found out that the devicetree needs to have the amo extention to work.
Somewhere there is a patch to split support into Zalrsc and Zaamo, but
here is one on my tree
https://github.com/Mr-Bossman/linux/commit/2bde8c4382a55cb82e769b0c8d9d8bf1b9c9164d

> Thanks,
> Jesse Taube
>
> > Testing done since v3: futex kselftests and perf futex tests. These tests caught the issues described below.
> > The same tests were executed on the Boston board with a single-hart P8700 core.
> >
> > Since the main issue was with an incorrectly written erratum, it shouldn't affect Vladimir's version [1].
> > However, since chips supporting only one part of the A extension are rare, we believe it might be
> > better to address this using the alternative mechanism, instead of demanding that the wider community
> > relax the A extension requirement.
> >
> > Changes in v4:
> > - The amo part of the ALT_TEST_AND_OP_BIT_ORD erratum erroneously hardcoded zero as the destination register.
> > This is fixed in v4.
> > - futex.h was missing the ANDN case.
> > - Link to v3: https://lore.kernel.org/r/20250901-p8700-zalrsc-v3-1-ec64fabbe093@xxxxxxxxxxxxx
> >
> > Changes in v3:
> > - Use alternatives to replace AMO instructions with LR/SC
> > - Rebase on Alexandre Ghiti's "for-next" branch.
> > - Link to v2: https://lore.kernel.org/linux-riscv/20241225082412.36727-1-arikalo@xxxxxxxxx/
> >
> > Links:
> > [1] https://lore.kernel.org/linux-riscv/20260120-lrsc-only-v2-0-a522e640d27d@xxxxxxxxxxxx/
> >
> > Signed-off-by: Aleksa Paunovic <aleksa.paunovic@xxxxxxxxxxxxx>
> > ---
> > arch/riscv/Kconfig.errata | 11 ++
> > arch/riscv/errata/mips/errata.c | 13 +-
> > arch/riscv/include/asm/atomic.h | 29 ++--
> > arch/riscv/include/asm/bitops.h | 28 ++--
> > arch/riscv/include/asm/cmpxchg.h | 9 +-
> > arch/riscv/include/asm/errata_list.h | 215 +++++++++++++++++++++++++++
> > arch/riscv/include/asm/errata_list_vendors.h | 3 +-
> > arch/riscv/include/asm/futex.h | 40 ++---
> > arch/riscv/kernel/entry.S | 10 +-
> > 9 files changed, 290 insertions(+), 68 deletions(-)
> >
> > diff --git a/arch/riscv/Kconfig.errata b/arch/riscv/Kconfig.errata
> > index 3c945d086c7d0266b685f9506d58b0662af071c4..cd5bd5e8eb395418c3ad103dbd836c775b7fd901 100644
> > --- a/arch/riscv/Kconfig.errata
> > +++ b/arch/riscv/Kconfig.errata
> > @@ -44,6 +44,17 @@ config ERRATA_MIPS_P8700_PAUSE_OPCODE
> >
> > If you are not using the P8700 processor, say n.
> >
> > +config ERRATA_MIPS_P8700_AMO_ZALRSC
> > + bool "Replace AMO instructions with LR/SC on MIPS P8700"
> > + depends on ERRATA_MIPS && 64BIT
> > + default n
> > + help
> > + The MIPS P8700 does not implement the full A extension,
> > + implementing only Zalrsc. Enabling this will replace
> > + all AMO instructions with LR/SC instructions on the P8700.
> > +
> > + If you are not using the P8700 processor, say n.
> > +
> > config ERRATA_SIFIVE
> > bool "SiFive errata"
> > depends on RISCV_ALTERNATIVE
> > diff --git a/arch/riscv/errata/mips/errata.c b/arch/riscv/errata/mips/errata.c
> > index e984a8152208c34690f89d8101571b097485c360..08c5efd58bf242d3831957f91f6338ef49f61238 100644
> > --- a/arch/riscv/errata/mips/errata.c
> > +++ b/arch/riscv/errata/mips/errata.c
> > @@ -23,13 +23,22 @@ static inline bool errata_probe_pause(void)
> > return true;
> > }
> >
> > -static u32 mips_errata_probe(void)
> > +static inline bool errata_probe_zalrsc(unsigned long archid)
> > +{
> > + return archid == 0x8000000000000201;
> > +}
> > +
> > +static u32 mips_errata_probe(unsigned long archid)
> > {
> > u32 cpu_req_errata = 0;
> >
> > if (errata_probe_pause())
> > cpu_req_errata |= BIT(ERRATA_MIPS_P8700_PAUSE_OPCODE);
> >
> > + if (errata_probe_zalrsc(archid))
> > + cpu_req_errata |= BIT(ERRATA_MIPS_P8700_ZALRSC);
> > +
> > +
> > return cpu_req_errata;
> > }
> >
> > @@ -38,7 +47,7 @@ void mips_errata_patch_func(struct alt_entry *begin, struct alt_entry *end,
> > unsigned int stage)
> > {

We should be patching this in at RISCV_ALTERNATIVES_EARLY_BOOT
This gives as few instructions as possible that aren't patched. Please
do something
similar to how thead does it.
https://elixir.bootlin.com/linux/v7.2-rc4/source/arch/riscv/errata/thead/errata.c#L222

Thanks,
Jesse Taube

> > struct alt_entry *alt;
> > - u32 cpu_req_errata = mips_errata_probe();
> > + u32 cpu_req_errata = mips_errata_probe(archid);
> > u32 tmp;
> >
> > BUILD_BUG_ON(ERRATA_MIPS_NUMBER >= RISCV_VENDOR_EXT_ALTERNATIVES_BASE);
> > diff --git a/arch/riscv/include/asm/atomic.h b/arch/riscv/include/asm/atomic.h
> > index 3f33dc54f94b2e14cb4270dbd0493625fbb977bd..9f848ec1705ff1afc6342e53965fab82309f9fe2 100644
> > --- a/arch/riscv/include/asm/atomic.h
> > +++ b/arch/riscv/include/asm/atomic.h
> > @@ -54,12 +54,9 @@ static __always_inline void arch_atomic64_set(atomic64_t *v, s64 i)
> > static __always_inline \
> > void arch_atomic##prefix##_##op(c_type i, atomic##prefix##_t *v) \
> > { \
> > - __asm__ __volatile__ ( \
> > - " amo" #asm_op "." #asm_type " zero, %1, %0" \
> > - : "+A" (v->counter) \
> > - : "r" (I) \
> > - : "memory"); \
> > -} \
> > + register __maybe_unused c_type ret, temp; \
> > + ALT_ATOMIC_OP(asm_op, I, asm_type, v, ret, temp); \
> > +}
> >
> > #ifdef CONFIG_GENERIC_ATOMIC64
> > #define ATOMIC_OPS(op, asm_op, I) \
> > @@ -89,24 +86,16 @@ static __always_inline \
> > c_type arch_atomic##prefix##_fetch_##op##_relaxed(c_type i, \
> > atomic##prefix##_t *v) \
> > { \
> > - register c_type ret; \
> > - __asm__ __volatile__ ( \
> > - " amo" #asm_op "." #asm_type " %1, %2, %0" \
> > - : "+A" (v->counter), "=r" (ret) \
> > - : "r" (I) \
> > - : "memory"); \
> > + register __maybe_unused c_type ret, temp; \
> > + ALT_ATOMIC_FETCH_OP_RELAXED(asm_op, I, asm_type, v, ret, temp); \
> > return ret; \
> > } \
> > static __always_inline \
> > c_type arch_atomic##prefix##_fetch_##op(c_type i, atomic##prefix##_t *v) \
> > -{ \
> > - register c_type ret; \
> > - __asm__ __volatile__ ( \
> > - " amo" #asm_op "." #asm_type ".aqrl %1, %2, %0" \
> > - : "+A" (v->counter), "=r" (ret) \
> > - : "r" (I) \
> > - : "memory"); \
> > - return ret; \
> > +{ \
> > + register __maybe_unused c_type ret, temp; \
> > + ALT_ATOMIC_FETCH_OP(asm_op, I, asm_type, v, ret, temp); \
> > + return ret; \
> > }
> >
> > #define ATOMIC_OP_RETURN(op, asm_op, c_op, I, asm_type, c_type, prefix) \
> > diff --git a/arch/riscv/include/asm/bitops.h b/arch/riscv/include/asm/bitops.h
> > index 3c1a15be54d804d7f609d8f4033710970f7b215f..caf8048c29f34182ee0740e836a1305c450b68f4 100644
> > --- a/arch/riscv/include/asm/bitops.h
> > +++ b/arch/riscv/include/asm/bitops.h
> > @@ -170,30 +170,27 @@ static __always_inline int variable_fls(unsigned int x)
> >
> > #if (BITS_PER_LONG == 64)
> > #define __AMO(op) "amo" #op ".d"
> > +#define __LR "lr.d"
> > +#define __SC "sc.d"
> > #elif (BITS_PER_LONG == 32)
> > #define __AMO(op) "amo" #op ".w"
> > +#define __LR "lr.w"
> > +#define __SC "sc.w"
> > #else
> > #error "Unexpected BITS_PER_LONG"
> > #endif
> >
> > #define __test_and_op_bit_ord(op, mod, nr, addr, ord) \
> > ({ \
> > - unsigned long __res, __mask; \
> > + __maybe_unused unsigned long __res, __mask, __temp; \
> > __mask = BIT_MASK(nr); \
> > - __asm__ __volatile__ ( \
> > - __AMO(op) #ord " %0, %2, %1" \
> > - : "=r" (__res), "+A" (addr[BIT_WORD(nr)]) \
> > - : "r" (mod(__mask)) \
> > - : "memory"); \
> > + ALT_TEST_AND_OP_BIT_ORD(op, mod, nr, addr, ord, __res, __mask, __temp); \
> > ((__res & __mask) != 0); \
> > })
> >
> > #define __op_bit_ord(op, mod, nr, addr, ord) \
> > - __asm__ __volatile__ ( \
> > - __AMO(op) #ord " zero, %1, %0" \
> > - : "+A" (addr[BIT_WORD(nr)]) \
> > - : "r" (mod(BIT_MASK(nr))) \
> > - : "memory");
> > + __maybe_unused unsigned long __res, __temp; \
> > + ALT_OP_BIT_ORD(op, mod, nr, addr, ord, __res, __temp);
> >
> > #define __test_and_op_bit(op, mod, nr, addr) \
> > __test_and_op_bit_ord(op, mod, nr, addr, .aqrl)
> > @@ -337,12 +334,9 @@ static __always_inline void arch___clear_bit_unlock(
> > static __always_inline bool arch_xor_unlock_is_negative_byte(unsigned long mask,
> > volatile unsigned long *addr)
> > {
> > - unsigned long res;
> > - __asm__ __volatile__ (
> > - __AMO(xor) ".rl %0, %2, %1"
> > - : "=r" (res), "+A" (*addr)
> > - : "r" (__NOP(mask))
> > - : "memory");
> > + __maybe_unused unsigned long res, temp;
> > +
> > + ALT_ARCH_XOR_UNLOCK(mask, addr, res, temp);
> > return (res & BIT(7)) != 0;
> > }
> >
> > diff --git a/arch/riscv/include/asm/cmpxchg.h b/arch/riscv/include/asm/cmpxchg.h
> > index 8712cf9c69dcb3690058c60e60481fc4c3ffea06..21035ebe0e9193c1793ddc5488346fcb04d3ff3a 100644
> > --- a/arch/riscv/include/asm/cmpxchg.h
> > +++ b/arch/riscv/include/asm/cmpxchg.h
> > @@ -56,13 +56,8 @@
> >
> > #define __arch_xchg(sfx, prepend, append, r, p, n) \
> > ({ \
> > - __asm__ __volatile__ ( \
> > - prepend \
> > - " amoswap" sfx " %0, %2, %1\n" \
> > - append \
> > - : "=r" (r), "+A" (*(p)) \
> > - : "r" (n) \
> > - : "memory"); \
> > + __typeof__(*(__ptr)) __maybe_unused temp; \
> > + ALT_ARCH_XCHG(sfx, prepend, append, r, p, n, temp); \
> > })
> >
> > #define _arch_xchg(ptr, new, sc_sfx, swap_sfx, prepend, \
> > diff --git a/arch/riscv/include/asm/errata_list.h b/arch/riscv/include/asm/errata_list.h
> > index 6694b5ccdcf85cfe7e767ea4de981b34f2b17b04..76c2f2a0f3b53f5507ecb2680d302679b3f97c69 100644
> > --- a/arch/riscv/include/asm/errata_list.h
> > +++ b/arch/riscv/include/asm/errata_list.h
> > @@ -25,6 +25,7 @@ ALTERNATIVE(__stringify(RISCV_PTR do_page_fault), \
> > __stringify(RISCV_PTR sifive_cip_453_page_fault_trp), \
> > SIFIVE_VENDOR_ID, ERRATA_SIFIVE_CIP_453, \
> > CONFIG_ERRATA_SIFIVE_CIP_453)
> > +
> > #else /* !__ASSEMBLER__ */
> >
> > #define ALT_SFENCE_VMA_ASID(asid) \
> > @@ -53,6 +54,220 @@ asm(ALTERNATIVE( \
> > : /* no inputs */ \
> > : "memory")
> >
> > +#ifdef CONFIG_ERRATA_MIPS_P8700_AMO_ZALRSC
> > +#define ALT_ATOMIC_OP(asm_op, I, asm_type, v, ret, temp) \
> > +asm(ALTERNATIVE( \
> > + " amo" #asm_op "." #asm_type " zero, %3, %0\n" \
> > + __nops(3), \
> > + "1: lr." #asm_type " %1, %0\n" \
> > + " " #asm_op " %2, %1, %3\n" \
> > + " sc." #asm_type " %2, %2, %0\n" \
> > + " bnez %2, 1b\n", \
> > + MIPS_VENDOR_ID, \
> > + ERRATA_MIPS_P8700_ZALRSC, \
> > + CONFIG_ERRATA_MIPS_P8700_AMO_ZALRSC) \
> > + : "+A" (v->counter), "=&r" (ret), "=&r" (temp) \
> > + : "r" (I) \
> > + : "memory")
> > +
> > +#define ALT_ATOMIC_FETCH_OP_RELAXED(asm_op, I, asm_type, v, ret, temp) \
> > +asm(ALTERNATIVE( \
> > + " amo" #asm_op "." #asm_type " %1, %3, %0\n" \
> > + __nops(3), \
> > + "1: lr." #asm_type " %1, %0\n" \
> > + " " #asm_op " %2, %1, %3\n" \
> > + " sc." #asm_type " %2, %2, %0\n" \
> > + " bnez %2, 1b\n", \
> > + MIPS_VENDOR_ID, \
> > + ERRATA_MIPS_P8700_ZALRSC, \
> > + CONFIG_ERRATA_MIPS_P8700_AMO_ZALRSC) \
> > + : "+A" (v->counter), "=&r" (ret), "=&r" (temp) \
> > + : "r" (I) \
> > + : "memory")
> > +
> > +#define ALT_ATOMIC_FETCH_OP(asm_op, I, asm_type, v, ret, temp) \
> > +asm(ALTERNATIVE( \
> > + " amo" #asm_op "." #asm_type ".aqrl %1, %3, %0\n"\
> > + __nops(3), \
> > + "1: lr." #asm_type ".aqrl %1, %0\n" \
> > + " " #asm_op " %2, %1, %3\n" \
> > + " sc." #asm_type ".aqrl %2, %2, %0\n" \
> > + " bnez %2, 1b\n", \
> > + MIPS_VENDOR_ID, \
> > + ERRATA_MIPS_P8700_ZALRSC, \
> > + CONFIG_ERRATA_MIPS_P8700_AMO_ZALRSC) \
> > + : "+A" (v->counter), "=&r" (ret), "=&r" (temp) \
> > + : "r" (I) \
> > + : "memory")
> > +/* BITOPS.h */
> > +#define ALT_TEST_AND_OP_BIT_ORD(op, mod, nr, addr, ord, __res, __mask, __temp) \
> > +asm(ALTERNATIVE( \
> > + __AMO(op) #ord " %0, %3, %1\n" \
> > + __nops(3), \
> > + "1: " __LR #ord " %0, %1\n" \
> > + #op " %2, %0, %3\n" \
> > + __SC #ord " %2, %2, %1\n" \
> > + "bnez %2, 1b\n", \
> > + MIPS_VENDOR_ID, \
> > + ERRATA_MIPS_P8700_ZALRSC, \
> > + CONFIG_ERRATA_MIPS_P8700_AMO_ZALRSC) \
> > + : "=&r" (__res), "+A" (addr[BIT_WORD(nr)]), "=&r" (__temp) \
> > + : "r" (mod(__mask)) \
> > + : "memory")
> > +
> > +#define ALT_OP_BIT_ORD(op, mod, nr, addr, ord, __res, __temp) \
> > +asm(ALTERNATIVE( \
> > + __AMO(op) #ord " zero, %3, %1\n" \
> > + __nops(3), \
> > + "1: " __LR #ord " %0, %1\n" \
> > + #op " %2, %0, %3\n" \
> > + __SC #ord " %2, %2, %1\n" \
> > + "bnez %2, 1b\n", \
> > + MIPS_VENDOR_ID, \
> > + ERRATA_MIPS_P8700_ZALRSC, \
> > + CONFIG_ERRATA_MIPS_P8700_AMO_ZALRSC) \
> > + : "=&r" (__res), "+A" (addr[BIT_WORD(nr)]), "=&r" (__temp) \
> > + : "r" (mod(BIT_MASK(nr))) \
> > + : "memory")
> > +
> > +#define ALT_ARCH_XOR_UNLOCK(mask, addr, __res, __temp) \
> > +asm(ALTERNATIVE( \
> > + __AMO(xor) ".rl %0, %3, %1\n" \
> > + __nops(3), \
> > + "1: " __LR ".rl %0, %1\n" \
> > + "xor %2, %0, %3\n" \
> > + __SC ".rl %2, %2, %1\n" \
> > + "bnez %2, 1b\n", \
> > + MIPS_VENDOR_ID, \
> > + ERRATA_MIPS_P8700_ZALRSC, \
> > + CONFIG_ERRATA_MIPS_P8700_AMO_ZALRSC) \
> > + : "=&r" (__res), "+A" (*addr), "=&r" (__temp) \
> > + : "r" (__NOP(mask)) \
> > + : "memory")
> > +
> > +#define ALT_ARCH_XCHG(sfx, prepend, append, r, p, n, temp) \
> > +asm(ALTERNATIVE( \
> > + prepend \
> > + " amoswap" sfx " %0, %3, %1\n" \
> > + __nops(2) \
> > + append, \
> > + prepend \
> > + "1: lr" sfx " %0, %1\n" \
> > + " sc" sfx " %2, %3, %1\n" \
> > + " bnez %2, 1b\n" \
> > + append, \
> > + MIPS_VENDOR_ID, \
> > + ERRATA_MIPS_P8700_ZALRSC, \
> > + CONFIG_ERRATA_MIPS_P8700_AMO_ZALRSC) \
> > + : "=&r" (r), "+A" (*(p)), "=&r" (temp) \
> > + : "r" (n) \
> > + : "memory")
> > +
> > +/* FUTEX.H */
> > +#define ALT_FUTEX_ATOMIC_OP(insn, ret, oldval, uaddr, oparg, temp) \
> > +asm(ALTERNATIVE( \
> > + "1: amo" #insn ".w.aqrl %[ov],%z[op],%[u]\n" \
> > + __nops(3) \
> > + "2:\n" \
> > + _ASM_EXTABLE_UACCESS_ERR(1b, 2b, %[r]), \
> > + "1: lr.w.aqrl %[ov], %[u]\n" \
> > + " " #insn" %[t], %[ov], %z[op]\n" \
> > + " sc.w.aqrl %[t], %[t], %[u]\n" \
> > + " bnez %[t], 1b\n" \
> > + "2:\n" \
> > + _ASM_EXTABLE_UACCESS_ERR(1b, 2b, %[r]), \
> > + MIPS_VENDOR_ID, \
> > + ERRATA_MIPS_P8700_ZALRSC, \
> > + CONFIG_ERRATA_MIPS_P8700_AMO_ZALRSC) \
> > + : [r] "+r" (ret), [ov] "=&r" (oldval), \
> > + [t] "=&r" (temp), [u] "+m" (*uaddr) \
> > + : [op] "Jr" (oparg) \
> > + : "memory")
> > +
> > +#define ALT_FUTEX_ATOMIC_SWAP(ret, oldval, uaddr, oparg, temp) \
> > +asm(ALTERNATIVE( \
> > + "1: amoswap.w.aqrl %[ov],%z[op],%[u]\n" \
> > + __nops(3) \
> > + "2:\n" \
> > + _ASM_EXTABLE_UACCESS_ERR(1b, 2b, %[r]), \
> > + "1: lr.w.aqrl %[ov], %[u]\n" \
> > + " mv %[t], %z[op]\n" \
> > + " sc.w.aqrl %[t], %[t], %[u]\n" \
> > + " bnez %[t], 1b\n" \
> > + "2:\n" \
> > + _ASM_EXTABLE_UACCESS_ERR(1b, 2b, %[r]), \
> > + MIPS_VENDOR_ID, \
> > + ERRATA_MIPS_P8700_ZALRSC, \
> > + CONFIG_ERRATA_MIPS_P8700_AMO_ZALRSC) \
> > + : [r] "+r" (ret), [ov] "=&r" (oldval), \
> > + [t] "=&r" (temp), [u] "+m" (*uaddr) \
> > + : [op] "Jr" (oparg) \
> > + : "memory")
> > +
> > +#else
> > +#define ALT_ATOMIC_OP(asm_op, I, asm_type, v, ret, temp) \
> > +asm("amo" #asm_op "." #asm_type " zero, %1, %0" \
> > + : "+A" (v->counter) \
> > + : "r" (I) \
> > + : "memory")
> > +
> > +#define ALT_ATOMIC_FETCH_OP_RELAXED(asm_op, I, asm_type, v, ret, temp) \
> > +asm("amo" #asm_op "." #asm_type " %1, %2, %0" \
> > + : "+A" (v->counter), "=r" (ret) \
> > + : "r" (I) \
> > + : "memory")
> > +
> > +#define ALT_ATOMIC_FETCH_OP(asm_op, I, asm_type, v, ret, temp) \
> > +asm("amo" #asm_op "." #asm_type ".aqrl %1, %2, %0" \
> > + : "+A" (v->counter), "=r" (ret) \
> > + : "r" (I) \
> > + : "memory")
> > +
> > +#define ALT_TEST_AND_OP_BIT_ORD(op, mod, nr, addr, ord, __res, __mask, __temp) \
> > +asm(__AMO(op) #ord " %0, %2, %1" \
> > + : "=r" (__res), "+A" (addr[BIT_WORD(nr)]) \
> > + : "r" (mod(__mask)) \
> > + : "memory")
> > +
> > +#define ALT_OP_BIT_ORD(op, mod, nr, addr, ord, __res, __temp) \
> > +asm(__AMO(op) #ord " zero, %1, %0" \
> > + : "+A" (addr[BIT_WORD(nr)]) \
> > + : "r" (mod(BIT_MASK(nr))) \
> > + : "memory")
> > +
> > +#define ALT_ARCH_XOR_UNLOCK(mask, addr, __res, __temp) \
> > +asm(__AMO(xor) ".rl %0, %2, %1" \
> > + : "=r" (res), "+A" (*addr) \
> > + : "r" (__NOP(mask)) \
> > + : "memory")
> > +
> > +#define ALT_ARCH_XCHG(sfx, prepend, append, r, p, n, temp) \
> > +asm(prepend \
> > + " amoswap" sfx " %0, %2, %1\n" \
> > + append \
> > + : "=r" (r), "+A" (*(p)) \
> > + : "r" (n) \
> > + : "memory")
> > +
> > +#define ALT_FUTEX_ATOMIC_OP(insn, ret, oldval, uaddr, oparg, temp) \
> > +asm("1: amo" #insn ".w.aqrl %[ov],%z[op],%[u]\n" \
> > + "2:\n" \
> > + _ASM_EXTABLE_UACCESS_ERR(1b, 2b, %[r]) \
> > + : [r] "+r" (ret), [ov] "=&r" (oldval), \
> > + [u] "+m" (*uaddr) \
> > + : [op] "Jr" (oparg) \
> > + : "memory")
> > +
> > +#define ALT_FUTEX_ATOMIC_SWAP(ret, oldval, uaddr, oparg, temp) \
> > +asm("1: amoswap.w.aqrl %[ov],%z[op],%[u]\n" \
> > + "2:\n" \
> > + _ASM_EXTABLE_UACCESS_ERR(1b, 2b, %[r]) \
> > + : [r] "+r" (ret), [ov] "=&r" (oldval), \
> > + [u] "+m" (*uaddr) \
> > + : [op] "Jr" (oparg) \
> > + : "memory")
> > +#endif
> > +
> > /*
> > * _val is marked as "will be overwritten", so need to set it to 0
> > * in the default case.
> > diff --git a/arch/riscv/include/asm/errata_list_vendors.h b/arch/riscv/include/asm/errata_list_vendors.h
> > index ec7eba3734371a2d8b68fbd4cbd88a8e7135a413..d47a98ab93d12ce1f6ae44449f80bb703987e985 100644
> > --- a/arch/riscv/include/asm/errata_list_vendors.h
> > +++ b/arch/riscv/include/asm/errata_list_vendors.h
> > @@ -23,7 +23,8 @@
> >
> > #ifdef CONFIG_ERRATA_MIPS
> > #define ERRATA_MIPS_P8700_PAUSE_OPCODE 0
> > -#define ERRATA_MIPS_NUMBER 1
> > +#define ERRATA_MIPS_P8700_ZALRSC 1
> > +#define ERRATA_MIPS_NUMBER 2
> > #endif
> >
> > #endif /* ASM_ERRATA_LIST_VENDORS_H */
> > diff --git a/arch/riscv/include/asm/futex.h b/arch/riscv/include/asm/futex.h
> > index 90c86b115e008a1fb08f3da64382fb4a64d9cc2f..bc3e8c0586410d1fc3a1a7d35b7775f9c339719f 100644
> > --- a/arch/riscv/include/asm/futex.h
> > +++ b/arch/riscv/include/asm/futex.h
> > @@ -12,6 +12,7 @@
> > #include <linux/errno.h>
> > #include <asm/asm.h>
> > #include <asm/asm-extable.h>
> > +#include <asm/errata_list.h>
> >
> > /* We don't even really need the extable code, but for now keep it simple */
> > #ifndef CONFIG_MMU
> > @@ -19,48 +20,47 @@
> > #define __disable_user_access() do { } while (0)
> > #endif
> >
> > -#define __futex_atomic_op(insn, ret, oldval, uaddr, oparg) \
> > +#define __futex_atomic_op(insn, ret, oldval, uaddr, oparg, temp) \
> > { \
> > __enable_user_access(); \
> > - __asm__ __volatile__ ( \
> > - "1: " insn " \n" \
> > - "2: \n" \
> > - _ASM_EXTABLE_UACCESS_ERR(1b, 2b, %[r]) \
> > - : [r] "+r" (ret), [ov] "=&r" (oldval), \
> > - [u] "+m" (*uaddr) \
> > - : [op] "Jr" (oparg) \
> > - : "memory"); \
> > + ALT_FUTEX_ATOMIC_OP(insn, ret, oldval, uaddr, oparg, temp); \
> > + __disable_user_access(); \
> > +}
> > +
> > +#define __futex_atomic_swap(ret, oldval, uaddr, oparg, temp) \
> > +{ \
> > + __enable_user_access(); \
> > + ALT_FUTEX_ATOMIC_SWAP(ret, oldval, uaddr, oparg, temp); \
> > __disable_user_access(); \
> > }
> >
> > static inline int
> > arch_futex_atomic_op_inuser(int op, int oparg, int *oval, u32 __user *uaddr)
> > {
> > - int oldval = 0, ret = 0;
> > + int __maybe_unused oldval = 0, ret = 0, temp = 0;
> >
> > if (!access_ok(uaddr, sizeof(u32)))
> > return -EFAULT;
> >
> > switch (op) {
> > case FUTEX_OP_SET:
> > - __futex_atomic_op("amoswap.w.aqrl %[ov],%z[op],%[u]",
> > - ret, oldval, uaddr, oparg);
> > + __futex_atomic_swap(ret, oldval, uaddr, oparg, temp);
> > break;
> > case FUTEX_OP_ADD:
> > - __futex_atomic_op("amoadd.w.aqrl %[ov],%z[op],%[u]",
> > - ret, oldval, uaddr, oparg);
> > + __futex_atomic_op(add,
> > + ret, oldval, uaddr, oparg, temp);
> > break;
> > case FUTEX_OP_OR:
> > - __futex_atomic_op("amoor.w.aqrl %[ov],%z[op],%[u]",
> > - ret, oldval, uaddr, oparg);
> > + __futex_atomic_op(or,
> > + ret, oldval, uaddr, oparg, temp);
> > break;
> > case FUTEX_OP_ANDN:
> > - __futex_atomic_op("amoand.w.aqrl %[ov],%z[op],%[u]",
> > - ret, oldval, uaddr, ~oparg);
> > + __futex_atomic_op(and,
> > + ret, oldval, uaddr, ~oparg, temp);
> > break;
> > case FUTEX_OP_XOR:
> > - __futex_atomic_op("amoxor.w.aqrl %[ov],%z[op],%[u]",
> > - ret, oldval, uaddr, oparg);
> > + __futex_atomic_op(xor,
> > + ret, oldval, uaddr, oparg, temp);
> > break;
> > default:
> > ret = -ENOSYS;
> > diff --git a/arch/riscv/kernel/entry.S b/arch/riscv/kernel/entry.S
> > index 60eb221296a604694c5f936d0c23c637dc44298e..8a7f9cb57f8450fd04107e2b57096c41bcefb722 100644
> > --- a/arch/riscv/kernel/entry.S
> > +++ b/arch/riscv/kernel/entry.S
> > @@ -73,7 +73,15 @@
> > beq a2, zero, .Lnew_vmalloc_restore_context
> >
> > /* Atomically reset the current cpu bit in new_vmalloc */
> > - amoxor.d a0, a1, (a0)
> > + ALTERNATIVE("amoxor.d a0, a1, (a0); \
> > + .rept 3; nop; .endr;",
> > + "1: lr.d a2, (a0); \
> > + xor a2, a2, a1; \
> > + sc.d a2, a2, (a0); \
> > + bnez a2, 1b;",
> > + MIPS_VENDOR_ID,
> > + ERRATA_MIPS_P8700_ZALRSC,
> > + CONFIG_ERRATA_MIPS_P8700_AMO_ZALRSC)
> >
> > /* Only emit a sfence.vma if the uarch caches invalid entries */
> > ALTERNATIVE("sfence.vma", "nop", 0, RISCV_ISA_EXT_SVVPTC, 1)
> >
> > ---
> > base-commit: c369299895a591d96745d6492d4888259b004a9e
> > change-id: 20250714-p8700-zalrsc-f3894be40d06
> >
> > Best regards,
> > --
> > Aleksa Paunovic <aleksa.paunovic@xxxxxxxxxxxxx>
> >
> >
> >
> > _______________________________________________
> > linux-riscv mailing list
> > linux-riscv@xxxxxxxxxxxxxxxxxxx
> > http://lists.infradead.org/mailman/listinfo/linux-riscv
> >