Re: [RFC V2 3/8] powerpc: introduce arch_enter_from_user_mode

Shrikanth Hegde
2025-09-14T09:03:35Z

On 9/9/25 2:32 AM, Mukesh Kumar Chaurasiya wrote:
> - Implement the hook arch_enter_from_user_mode for syscall entry.

nit: for generic syscall infra.

> - Move booke_load_dbcr0 from interrupt.c to interrupt.h
>
> No functional change intended.
>
> Signed-off-by: Mukesh Kumar Chaurasiya <mchauras@linux.ibm.com>
> ---
> arch/powerpc/include/asm/entry-common.h | 96 +++++++++++++++++++++++++
> arch/powerpc/include/asm/interrupt.h | 23 ++++++
> arch/powerpc/kernel/interrupt.c | 22 ------
> 3 files changed, 119 insertions(+), 22 deletions(-)
>
> diff --git a/arch/powerpc/include/asm/entry-common.h b/arch/powerpc/include/asm/entry-common.h
> index 3af16d821d07e..49607292bf5a5 100644
> --- a/arch/powerpc/include/asm/entry-common.h
> +++ b/arch/powerpc/include/asm/entry-common.h
> @@ -5,7 +5,103 @@
>
> #ifdef CONFIG_GENERIC_IRQ_ENTRY
>
> +#include <asm/cputime.h>
> +#include <asm/interrupt.h>
> #include <asm/stacktrace.h>
> +#include <asm/tm.h>
> +
> +static __always_inline void arch_enter_from_user_mode(struct pt_regs *regs)
> +{
> + if (IS_ENABLED(CONFIG_PPC_IRQ_SOFT_MASK_DEBUG))
> + BUG_ON(irq_soft_mask_return() != IRQS_ALL_DISABLED);
> +
> + BUG_ON(regs_is_unrecoverable(regs));
> + BUG_ON(!user_mode(regs));
> + BUG_ON(regs_irqs_disabled(regs));
> +
> +#ifdef CONFIG_PPC_PKEY
> + if (mmu_has_feature(MMU_FTR_PKEY)) {
> + unsigned long amr, iamr;
> + bool flush_needed = false;
> + /*
> + * When entering from userspace we mostly have the AMR/IAMR
> + * different from kernel default values. Hence don't compare.
> + */
> + amr = mfspr(SPRN_AMR);
> + iamr = mfspr(SPRN_IAMR);
> + regs->amr = amr;
> + regs->iamr = iamr;
> + if (mmu_has_feature(MMU_FTR_KUAP)) {
> + mtspr(SPRN_AMR, AMR_KUAP_BLOCKED);
> + flush_needed = true;
> + }
> + if (mmu_has_feature(MMU_FTR_BOOK3S_KUEP)) {
> + mtspr(SPRN_IAMR, AMR_KUEP_BLOCKED);
> + flush_needed = true;
> + }
> + if (flush_needed)
> + isync();
> + } else
> +#endif
> + kuap_assert_locked();
> +
> + booke_restore_dbcr0();
> +
> + account_cpu_user_entry();
> +
> + account_stolen_time();
> +
> + /*
> + * This is not required for the syscall exit path, but makes the
> + * stack frame look nicer. If this was initialised in the first stack
> + * frame, or if the unwinder was taught the first stack frame always
> + * returns to user with IRQS_ENABLED, this store could be avoided!
> + */
> + irq_soft_mask_regs_set_state(regs, IRQS_ENABLED);
> +
> + /*
> + * If system call is called with TM active, set _TIF_RESTOREALL to
> + * prevent RFSCV being used to return to userspace, because POWER9
> + * TM implementation has problems with this instruction returning to
> + * transactional state. Final register values are not relevant because
> + * the transaction will be aborted upon return anyway. Or in the case
> + * of unsupported_scv SIGILL fault, the return state does not much
> + * matter because it's an edge case.
> + */
> + if (IS_ENABLED(CONFIG_PPC_TRANSACTIONAL_MEM) &&
> + unlikely(MSR_TM_TRANSACTIONAL(regs->msr)))
> + set_bits(_TIF_RESTOREALL, &current_thread_info()->flags);
> +
> + /*
> + * If the system call was made with a transaction active, doom it and
> + * return without performing the system call. Unless it was an
> + * unsupported scv vector, in which case it's treated like an illegal
> + * instruction.
> + */
> +#ifdef CONFIG_PPC_TRANSACTIONAL_MEM
> + if (unlikely(MSR_TM_TRANSACTIONAL(regs->msr)) &&
> + !trap_is_unsupported_scv(regs)) {
> + /* Enable TM in the kernel, and disable EE (for scv) */
> + hard_irq_disable();
> + mtmsr(mfmsr() | MSR_TM);
> +
> + /* tabort, this dooms the transaction, nothing else */
> + asm volatile(".long 0x7c00071d | ((%0) << 16)"
> + :: "r"(TM_CAUSE_SYSCALL|TM_CAUSE_PERSISTENT));
> +
> + /*
> + * Userspace will never see the return value. Execution will
> + * resume after the tbegin. of the aborted transaction with the
> + * checkpointed register state. A context switch could occur
> + * or signal delivered to the process before resuming the
> + * doomed transaction context, but that should all be handled
> + * as expected.
> + */
> + return;
> + }
> +#endif // CONFIG_PPC_TRANSACTIONAL_MEM

nit: Better to follow standard comment practices.
/* CONFIG_PPC_TRANSACTIONAL_MEM */

> +}
> +#define arch_enter_from_user_mode arch_enter_from_user_mode
>
> #endif /* CONFIG_GENERIC_IRQ_ENTRY */
> #endif /* _ASM_PPC_ENTRY_COMMON_H */
> diff --git a/arch/powerpc/include/asm/interrupt.h b/arch/powerpc/include/asm/interrupt.h
> index 56bc8113b8cde..6edf064a0fea2 100644
> --- a/arch/powerpc/include/asm/interrupt.h
> +++ b/arch/powerpc/include/asm/interrupt.h
> @@ -138,6 +138,29 @@ static inline void nap_adjust_return(struct pt_regs *regs)
> #endif
> }
>
> +static inline void booke_load_dbcr0(void)
> +{
> +#ifdef CONFIG_PPC_ADV_DEBUG_REGS
> + unsigned long dbcr0 = current->thread.debug.dbcr0;
> +
> + if (likely(!(dbcr0 & DBCR0_IDM)))
> + return;
> +
> + /*
> + * Check to see if the dbcr0 register is set up to debug.
> + * Use the internal debug mode bit to do this.
> + */
> + mtmsr(mfmsr() & ~MSR_DE);
> + if (IS_ENABLED(CONFIG_PPC32)) {
> + isync();
> + global_dbcr0[smp_processor_id()] = mfspr(SPRN_DBCR0);
> + }
> + mtspr(SPRN_DBCR0, dbcr0);
> + mtspr(SPRN_DBSR, -1);
> +#endif
> +}
> +

Please run checkpatch.pl --strict on the series and fix the simple
ones such as need to using tabs, spaces and alignments, extra lines etc.

> +
> static inline void booke_restore_dbcr0(void)
> {
> #ifdef CONFIG_PPC_ADV_DEBUG_REGS
> diff --git a/arch/powerpc/kernel/interrupt.c b/arch/powerpc/kernel/interrupt.c
> index 0d8fd47049a19..2a09ac5dabd62 100644
> --- a/arch/powerpc/kernel/interrupt.c
> +++ b/arch/powerpc/kernel/interrupt.c
> @@ -78,28 +78,6 @@ static notrace __always_inline bool prep_irq_for_enabled_exit(bool restartable)
> return true;
> }
>
> -static notrace void booke_load_dbcr0(void)
> -{
> -#ifdef CONFIG_PPC_ADV_DEBUG_REGS
> - unsigned long dbcr0 = current->thread.debug.dbcr0;
> -
> - if (likely(!(dbcr0 & DBCR0_IDM)))
> - return;
> -
> - /*
> - * Check to see if the dbcr0 register is set up to debug.
> - * Use the internal debug mode bit to do this.
> - */
> - mtmsr(mfmsr() & ~MSR_DE);
> - if (IS_ENABLED(CONFIG_PPC32)) {
> - isync();
> - global_dbcr0[smp_processor_id()] = mfspr(SPRN_DBCR0);
> - }
> - mtspr(SPRN_DBCR0, dbcr0);
> - mtspr(SPRN_DBSR, -1);
> -#endif
> -}
> -
> static notrace void check_return_regs_valid(struct pt_regs *regs)
> {
> #ifdef CONFIG_PPC_BOOK3S_64